What Are The Best Big Block Chevy Connecting Rod Bearing For The Money

The crankshaft, connecting rods, and pistons are frequently referred to as the rotating assembly, although, technically speaking, only the crank rotates during engine operation. The pistons are actually reciprocating parts, traveling up and down the bores with great alacrity while the rods connect the two and are partly rotating and partly reciprocating parts. When it comes to cranks, rods, and pistons, here's the bottom line: light is good, strong is better, but strong and light is best.

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Crankshafts

Stock big-block Chevy crankshafts were available in only two strokes: 3.760 inches (in 396, 402, and 427 engines) and 4.000 inches (in 454 and 502 V-8s), and were made from either cast iron or forged low-carbon steel like AISI (American Iron and Steel Institute) 1053, although a few 4.000-inch-stroke cranks were produced from 5140 alloy steel. When the 396- and 427-ci Rat motors appeared in the mid 1960s, all were equipped with forged steel cranks that were dimensionally interchangeable, although they had slight differences in the counterweights and were balanced to different specs. If you want to use a 396 crank to build a 427, you won't have any problems other than having to re-balance the rotating assembly, which should always be done anyway. All 396, 402, and 427 engines were internally balanced and used neutral balance harmonic dampeners and flywheels or flexplates.

High quality 4340 forged steel stroker crankshaft, H-beam connecting rods, and forged aluminum pistons are a wise investment for any highperformance big block.

The Mark IV crank (left) is designed for use with two-piece real main seals, and the Gen V/VI crank (right) is for use with a one-piece rear main seal. Both of these Scat 4340 cranks are balanced for use with neutral-balance flywheels; note the prominent balance pad at the rear of the Mark IV crank, which negates the need for stock-spec externally balanced wheels.

Cast-iron cranks are easily identified by the thin casting line visible on the counterweights and rod throws. This Gen V/VI 454 crank has a one-piece rear main seal and a steel trigger wheel on the nose for a crank position sensor. Use the trigger wheel for correct harmonic dampener spacing, even if you are building a non-EFI Gen V/ VI engine. If you remove the wheel, your crank pulley does not line up correctly with the water pump and alternator pulleys. Note that Gen V/VI cast-iron cranks require a different flexplate or flywheel than forged steel Gen V/VI cranks due to differences in the balance.

This high-quality Scat 4.250-inch-stroke crank is a traditional Mark IV design for use with two-piece rear main seals, and it is forged from 4340 alloy steel and fully nitrided for improved strength. It has several design improvements over stock cranks, including lightening holes in all four rod journals, scalloped cuts at the flywheel flange, and streamlined counterweights with bullet-shaped leading edges and tapered trailing edges to reduce oil windage. All external surfaces have been smoothed to reduce stress risers and improve oil shedding, thus the typical wide forging line is no longer visible. The counterweights have been specifically designed to allow use with neutral-balance (396- and 427-style) harmonic dampeners and flywheels.

Big-block Chevy cranks may have either one, two (left), or three (right) keyways in the crank snout, which are used to align the crank timing sprocket or gear and the harmonic dampener. Some shops offer the option of larger-than-stock 1/4-inch keyways located 180 degrees apart for supercharged engines, due to the tremendous strain put on the bottom blower pulley. Stock woodruff keys are 3/16 inch wide x 3/4 inch long.

This 4340 Scat crank features counterweight profiling to reduce windage and drag as the crank rotates through the suspended oil in the crankcase. The leading edges are rounded (left), and the trailing edges are tapered (right), which is the correct aerodynamic shape for best reducing frictional losses. Some cranks have counterweights that are knife-edged on the leading edge, but that's not the shape you see on the nose of a nuclear-powered submarine, is it?

Aftermarket cranks feature much-largerthan- stock journal fillet radii for increased strength, plus chamfered oil holes for improved lubrication. This rod journal also has been through-drilled to reduce weight for quicker acceleration.

This Manley connecting rod has been fitted with an HN series Clevite bearing designed to give more clearance with a large fillet radius crank. The generous chamfer on the rod always goes against the cheek of the crank throw, so oddnumbered cylinders get the rod installed with the chamfer toward the front of the engine, and even-numbered cylinders have the chamfer facing the rear.

This 4.500-inch-stroke fully counterweighted Crower super-light crankshaft has small-block Chevy rod journals measuring 2.100 inches, compared to the standard big-block size of 2.200 inches. Smaller journals reduce bearing speed and allow a connecting rod with a smaller big end for more crankcase and camshaft clearance with the long stroke. Although it adds extra weight, center counterweights are beneficial for controlling crank harmonics and achieving better balance of the rotating assembly.

Cast-iron cranks started showing up when the Rat motor was tapped into service for non-high-performance passenger cars. When the 454 made its debut in 1970, most were equipped with forged steel cranks, but it was subsequently relegated to duty in trucks only after 1974 and most then featured cast-iron crankshafts, which are most commonly found when searching through a pile of crank cores at your local auto parts recycler (fancy talk for junkyard).

It's easy to tell the difference between a stock cast and forged steel crank by looking at the parting line, which is visible between the machined surfaces of the crank. A thin line indicates a castiron crank; and all forged steel cranks have a hefty 3/4- to 1-inch-wide parting line. Also, forged steel cranks ring like a bell when tapped lightly with a small hammer or other mallet. This is also a tried-and-true method of detecting cracks in forged cranks: when most of the counterweights ring clearly, and one produces a muffled "clunk," it's a pretty safe bet than there is a crack in that area. All factory-produced 4.000-inch-stroke engines were externally balanced and used specific harmonic dampeners and flexplates (or flywheels) with extra balance weight built into them. You must always use the appropriate balancer and flexplate for your engine, or the resulting imbalance quickly helps you to disassemble the engine, maybe even without using tools.

Gen V and Gen VI cranks are readily identified by the large rear seal/flywheel flange developed for use with the onepiece rear main seal. The flywheels and flexplates used with these cranks have the same six-on-3.58-inch bolt pattern as Mark IV wheels, but they require specific flywheels or flexplates that are balanced differently than the Mark IV engines. Also, Gen V/VI engines used flywheels or flexplates with a cast crank different than those with a forged steel crank. The bolt pattern is the same, but they are balanced differently. All high-performance bigblocks should be equipped with an aftermarket flywheel or flexplate meeting SFI specs anyway, so just be sure you order the wheel that fits your crank. All other critical dimensions such as main journal diameter (2.750 inches), rod journal diameter (2.200 inches), overall length, journal spacing, and crank snout diameter (1.600 inches) are the same for production Mark IV and Gen V/VI cranks.

Harmonic dampeners are interchangeable among Mark IV and Gen V/VI engines, but you must be sure to use the correct balance for your rotating assembly, whether neutral balance (396/427 style) or externally balanced (454/502 style). Note that most aftermarket cranks intended for competition use are neutrally balanced, and must be used with matching neutral-balance dampeners and flywheels/flexplates.

The automotive aftermarket has really stepped up to the plate in terms of big-block crankshafts suitable for all levels of performance, offering economical cast cranks, forged steel cranks made from superior alloys, and even billet steel cranks for the ultimate in material strength and custom features. There are a plethora of high-quality crankshafts for the big-block Chevy from manufacturers such as BRC, Bryant, Callies, Cola, Crower, Eagle, K1 Technologies, Lunati, Ohio Crankshaft, Winberg, Scat, and probably others by the time you read this.

Of course, the primary benefit of going to an aftermarket crank is to increase the stroke (the distance which the pistons travel up and down the bore), which increases the displacement of your engine and always generates more torque and horsepower, unless you select engine parts that are so mismatched that even the stroker crank doesn't help.

An example might be to select a quarter-inch stroker (stock plus 1/4 inch, or 4.250 inches) for your car-hauler truck engine with small port heads and an extremely short-duration/low-lift "mileage" cam. The small ports and short cam timing might have worked well to pump up the low-end power of the stock 454. But the stroker crank further increases the velocity of the air/fuel charge and the extra displacement also increases the compression ratio (if the piston top design remains the same as before), so now it is likely that this 496 combo is prone to pre-ignition from excessive compression for the pump gas being used.

The simple solution is to change the cam to a design that is matched to this new combination, and change the heads to aftermarket aluminum pieces with bigger ports and better combustion chamber heat dissipation characteristics. But other than this obscure example, installing a stroker crank in your hot rod or competition big-block is a win-win proposition.

Aftermarket cranks typically use a larger fillet radius where the journal meets the sides of the counterweight to reduce the stress concentration at this critical point. This requires that you select rod and main bearings designed with additional clearance for the larger radius, or you have to clearance the bearing yourself. Old-timers are familiar with the concept of scraping bearings: the bearing material is soft enough that you can carve it into shape with a bearing knife. (Now you know why they taught you to carve in Boy Scouts.) You're generally better advised to just order performance bearing inserts, which are narrower than stock bearings. Your crank manufacturer can advise you which part numbers work with the radius on your particular crank, but even so, you should always check to be sure the bearings aren't binding against the oversized fillet radius.

In normally aspirated applications for maximum effort, it's common to reduce the crank journal diameters to reduce bearing drag and free up a little more power. This kind of effort pays very little power dividends and does so at the expense of some crankshaft strength, so it's certainly not a good idea for the average street or bracket race engine or any competition engine with power adders such as nitrous oxide injection, blowers, or turbochargers.

Reducing the rod journals from the stock 2.200-inch diameter to 2.100 or even 2.000 inches is easily accomplished using custom connecting rods with small-block Chevy rod bearing inserts. Pro Stockers typically go even further, reducing the journal diameter to 1.889 inches and running Honda bearings. Pro Stockers also typically run 409 Chevy main bearings with a 2.500-inch main journal. While it is possible to fabricate bearing spacers to adapt the 409 main bearings to a standard block, doing it the right way requires a custom block supplied with undersized main bores not for the faint of heart, or light of wallet.

Inspection, Preparation and Repair

The first step in crank inspection is to just look it over carefully, checking for obvious cracks, deep scoring, heatblackened journals, stripped bolt-holes, etc. Cracks large enough to be visible to the naked eye are grounds for dismissal of any crank; they normally can't be repaired. Other problems can usually be corrected by a reputable crank repair shop, but you have to weigh the cost versus the value of the crank. Generally, stock 3.760- and 4.000-inch-stoke cranks that have any of these problems, other than minor scoring on the journals, should not be used because they are going to cost more to repair than they are worth. More costly aftermarket cranks might be worth repairing, and a good shop should be able to give you an estimate for repairs before you commit to the job.

Regardless of whether or not the crank appears to need other work, you should always have it Magnaflux tested to reveal any cracks, which are a deal breaker as far as that crank goes. A good crank shop can straighten your crank, weld up badly scored journals, re-grind to fit standard or undersize bearings, Helicoil stripped bolt-holes, true the flywheel flange, re-harden the crank, and just about anything else you can think a crank might need, but cannot fix deep cracks. So do the Magnaflux thing first, and save yourself a lot of grief and wasted money. If the crank doesn't pass this first step, consider it money well spent, knowing that a crank failure in a running engine usually destroys the entire short block, and sometimes even damages the upper end of the engine.

If your crank passes the visual inspection, the next area of concern is whether the journals can be used as-is, with just a polish, or if they need to be ground undersize. Oversize bearings are available in .001-, .010-, .020-, .030-, and .040-inch sizes, and you should measure the journals with a dial caliper or micrometer to see if they are standard (2.750-inch mains, 2.200- inch rod journals) or have already been undercut. In gearhead lingo, cranks are described as "standard/standard, ten/ten (.010/.010 inch)" or some combination of sizes indicating how much (in thousandths of an inch) the crank has been ground undersize on the mains and rod journals. Excessive undercuts are generally viewed as a negative, because they indicate that the crank has had a long, hard life, and if the crank was induction hardened, you may be getting into the softer core layer of steel, requiring the crank to be re-hardened after further grinding. Remember, most aftermarket cranks were hardened by nitriding, Tufftriding, or some other method which usually only penetrates to a depth of a few thousandths of an inch, so re-hardening is mandatory after grinding the journals. Cast-iron cranks do not need to be hardened, even after regrinding.

Restoring Balance

The need to balance any spinning mechanism that rotates at high speeds is pretty obvious, but when part of that assembly is actually reciprocating (moving up and down along the centerline of the bore) instead of rotating, it complicates matters. You can't simply balance a crank in the same fashion that you spin balance your wheels and tires, for instance, but instead you or your engine balancer uses a formula to determine the bob weight, or effective weight of the rods, bearings, pistons, wrist pins, and rings as they affect the balance of the crankshaft.

The standard formula is:

Bob Weight = Rotating Mass +

(Reciprocating Mass ÷ 2)

Where:

Rotating Mass = weight of the rod bearings plus the big end of the rod

Reciprocating Mass = weight of the pistons, rings, wrist pins and retainers, plus the small end of the rod

Because two piston/rod assemblies attach to each crank journal, the final calculated weight is doubled and then clamped onto each crank rod journal using carefully weighed bob weights to duplicate the forces acting on the crank as it spins.

In addition to the crank and piston/ rod assembly components, you also need to supply the engine balancer with your harmonic dampener and flywheel or flexplate. While externally balanced big-blocks like the 454 and 502 are commonly used in high-performance street applications, most high-end performance and racing engines benefit from having a neutral- or internal-balance condition. You can achieve correct balance with external weights on the harmonic dampener and flywheel, but the resulting vector forces and harmonic vibrations are transmitted along the length of the crankshaft to the counterweighted parts hanging off each end of the crank, and that can have detrimental effects on bearing life and crankshaft integrity.

To achieve a neutral balance with long-stroke crankshafts, it is usually necessary to add heavy-metal weights to the counterweights by drilling and reaming large holes in the counterweights, then pressing in a slug of Mallory metal to add weight where needed. The holes must be parallel to the crank axis so that centrifugal force doesn't dislodge them at high engine speeds. This adds cost to the balancing operation, but is well worth it in the long run.

Connecting Rods

Stock big-block Chevy rods are I-beam designs (the cross-section of the main beam resembles a capital letter I), and they were all made from forged steel with the same basic dimensions: .990-inch-diameter pin bores (the small end), 2.324-inch-diameter big end to accept the 2.2025-inch inside diameter rod bearings, with a hole center-to-center length of 6.135 inches. Two threaded fasteners on each side of the big end allow the rod cap to be removed for installation on the crankshaft journal.

Stock rod bolts were either 3/8 (most passenger car and truck applications) or 7/16 inch (high-performance applications), have a shaped head to register securely against a shoulder on the main section of the rod, and are knurled to tightly align the main section of the rod with the rod cap. There have only been three types of big-block rods in production engines: the standard passenger car rod ("dog-bone" rods, named after the shape of the forging relief on the beam section), truck rods (with their Q-Tip–shaped relief on the beam), and high-performance "dot" rods (with a distinctive dot cast into the upper portion of the beam relief). These high-performance rods are often erroneously referred to as "dimple" rods, but that is not accurate. Dimples go in, not out. Let's agree to call them dot rods or hi-po rods. The highperformance rods initially used 3/8-inch rod bolts in the 1960s, but subsequently changed to 7/16-inch bolts, which are stronger.

Stock cast piston with a press-fit pin. Note that no pin retainers are necessary with this setup. This four-ring piston is from a heavy-duty 427 truck engine, and that's why Chevrolet went with tall-deck (10.200 inches) blocks for those applications. The connecting rod is the standard "dog-bone" design with 3/8-inch rod bolts.

Chevy highperformance "dot" rod with 7/16-inch rod bolts is still a good choice for engines up to about 700 hp. There were three versions of these rods: one with 3/8-inch rod bolts and pressed pins (1965– 1969), one with 7/16- inch rod bolts and pressed pins (LS-6 and LS-7), and a version with 7/16-inch boron rod bolts and full-floating pins, which was used in Chevy's killer big-blocks, like the L88 and ZL-1.

GMPP PN 19170198 is a Magnafluxed 4340 steel rod with heavy-duty 7/16-inch bolts. It is a pressed-piston pin design used in Gen V and Gen VI 454 and 502 engines.

Round wire pin locks must be used with correctly sized and chamfered wrist pins.

Wrist pin walls may be straight in various thicknesses, or internally tapered on each end to reduce weight. Since tapered pins weigh less, they are popular for professional competition, but not as strong as straight-wall pins. If you see evidence of scuffing or cracks in the piston pin bores, the pins are flexing under load, and you should change to a stronger pin. Generally you're better off to go with a pin that is stronger than you think you need, rather than take a chance on the lightweight part. This is especially true in high-output engines or with heavy nitrous oxide or supercharged engines.

These JE pistons are getting the pin bores precisely honed to fit with the supplied wrist pins.

Spirolox rings are a good choice for wrist pin retention. They are a little tough to install and much harder to remove, which is what makes them so good; they want to stay in place. They can be spiraled into the lock groove easily with a little practice, but be sure not to stretch them out of shape during installation. Most piston manufacturers use two per side. Be sure to lube pin with assembly lube before final assembly, and replace Spirolox rings with new ones every time they are removed.

Forged aluminum piston, billet aluminum connecting rod, and heavy-wall wrist pin from a 1,200-plus-hp blown alcohol bigblock. Aluminum buttons are normally used to retain the wrist pin in competition engines with blowers and nitrous. Note the step in the buttons, necessary because the pin bore intersects the oil ring groove.

This high-quality, lightweight Crower I-beam rod is made from 4340 steel and is easily capable of handling more than 1,000 hp. Note that the shoulders of the beam section are profiled for clearance with long stroke big-blocks. It uses 2.100-inch small-block Chevy rod bearing inserts, which not only reduce friction, but allow the rod bolts to be moved closer together for improved rod-to-cam and rod-to-block clearance.

Due to the greater thermal expansion rate, aluminum rods must use pinned bearings in the cap to prevent spun bearings. Serrated parting line where the cap meets the beam section ensures positive registration. Note that hardened washers have a chamfered side, which must be installed facing the bolt head to clear the large under-head radius.

This vintage Bill Miller Engineering (BME) aluminum connecting rod features 2.100- inch small-block Chevy bearings. In addition to reduced bearing speed, the most important benefit of this design is how the standard forging is used, but with a smaller bore in the big end, resulting in a stronger cap-to-mainbody junction. Note wrist pin oil hole in top of rod. All full-floating pins must have an oiling provision.

Rods with full-floating pins require an oil hole to provide splash lubrication to the pin. This hole must be drilled before the small end is honed to final size. You can just barely see the pin oiling hole in the top of this Scat H-beam rod. Note the two relief cuts for the bearing tangs of the bigend bore. These two notches are always on the same side of the bore.

A connecting rod vice holds rods securely for torquing or loosening bolts on the workbench. You can use your shop vice with non-marring aluminum or brass inserts in a pinch.

All original equipment big-block rods are physically interchangeable. The standard passenger car rods (dogbone) are adequate for mild performance street engines up to about 500 hp. The truck rods (Q-Tip–shaped relief) are a bit stronger, and the hi-po rods have been used successfully on many 700-plushp engines. But (and this is a big but), it is usually not the rod itself that fails, it is the relatively weak-by-design rod fastener hardware. The OE (original equipment) design uses two nuts with a limited amount of thread engagement to secure the rod cap, and this is the weak link in the connecting rod chain. If you decide to use stock rods, invest in premium rod bolts and nuts from a reputable aftermarket company, such as ARP. Along with conventional replacement rod bolts made from superior steel, ARP has developed the Wave-Lok rod bolt. It features an undulating surface in place of the stress-inducing knurling of conventional rod bolts.

Before the advent of affordable aftermarket rods, it was standard practice to rebuild stock rods for performance applications. The usual procedure was to Magnaflux the rod to detect any cracks, grind and polish the forging lines on the side of the beam, shot-peen the rod to harden and improve the surface finish, bore and ream the small end for a bronze bushing (for full-floating pins), recondition the big-end to restore roundness and proper bearing crush, and then install highquality rod bolts. Whew! That's a lot of work and money to sink into parts that are still not as strong as the aftermarket rods that are readily available today. And to top it off, you can get the aftermarket rods in a variety of lengths (typically .250 or .400 inch longer than stock, plus many more) to take advantage of better rod/stroke ratios.

Most OEM rods used in passenger cars and light-duty trucks with cast pistons were installed with press-fit wrist pins. This is a very durable system of pin retention, but disassembly requires pushing the pin out with a hydraulic press, which usually damages the piston. Connecting rods for full-floating pins usually have the small end bored out for a bronze bushing that is then honed to a very precise clearance, usually less than .001 inch. The pin is retained in the piston with pin locks that snap into pin retainer grooves in the piston pin bore. Most street highperformance pistons and all racing pistons utilize full-floating pins, and there are several methods of retaining the pins.

Tru-Arcs are simple snap rings that are quite easy to install and remove, but most aftermarket pistons these days use Spirolox rings to retain the wrist pins. They are a pain to install and even harder to remove, and that's what makes them an excellent choice for wrist pin retention: you don't want your pins to come loose during engine operation. Round wire locks are another popular method of pin retention, but they require special wrist pins that are chamfered on the ends.

With full-floating pins, the pin-tolock end clearance is critical, since excessive clearance lets the pin batter against the locks, possibly knocking them out. Typical pin-to-retainer clearance is .0000 to .0005 inch. Wrist pin buttons are popular with builders of engines with extremely high horsepower, since they are very easy to install or remove, and absolutely can't be knocked loose. The downside to buttons is that they add weight to the reciprocating assembly, but pistons designed for use with a supercharger or lots of nitrous are usually pretty heavy already, and frequent piston changes are much easier with the buttons.

Because the fit between the wrist pin, piston pin bore, and pin retainers is so critical, most engine builders opt to buy pistons "pin fitted," meaning that the manufacturer has carefully machined and checked these clearances, and supplied the correctly sized pins with the piston. All that remains is to verify the pin-to-connecting-rod clearance, which normally runs from .0008 to .0012 inch. Engines with vacuum pumps may require a bit more clearance, since the pump tends to reduce the amount of oil available to lube the pin bore.

Aftermarket rods for the big-block are available in a variety of shapes and materials to suit various applications from manufacturers such as Bill Miller Engineering, BRC, Carillo, Crower, Eagle, GRP, Howard's, Lunati, Manley, Ohio Crankshaft, Oliver, Scat, Venolia, and others. There are steel rods available, usually made from very strong 4340 alloy steel, in I-beam and H-beam configurations; aluminum rods that are exclusively used for very-high-RPM drag racing; and even titanium rods for those of you with unlimited budgets. Titanium offers the strength of steel with the light weight of aluminum, but they are so expensive, the vast majority of big-block performance and racing engines are outfitted with either steel or aluminum.

I'm going to venture a rough estimate that 90 percent or more of today's performance and racing big-blocks use steel connecting rods for their brute strength and longevity. Yes, aluminum is lighter, but because it is not as strong as steel, aluminum rods must be physically much larger than steel rods, which limits their use in very-long-stroke engines because there just isn't enough room in the crankcase. Additionally, aluminum rods must be replaced regularly, usually after no more than 200 runs down the quartermile. Pro racers replace them even sooner.

One positive attribute of aluminum connecting rods is their ability to dampen severe shock loads, such as those that are common in supercharged, exotic fuel-burning engines, or with massive amounts of nitrous oxide. Aluminum rods are used in those types of engines to save the crankshaft and bearings from frequent failure, and replacement is just seen as part of the regular maintenance schedule for these fire-breathers. Also, aluminum rods expand more when they get hot, so rod bearings must be drilled for an anti-rotation dowel (which is pressed into the cap), and minimum piston-to-head clearance must be at least .050 inch (consult with your piston/rod manufacturer for their specs) to allow for the aluminum rod growth.

Rod Length

In this section, I'm going to butcher and barbecue a few sacred cows that have been worshiped for the past few decades. I'll get right to the point: the job of the connecting rod is to connect the piston to the crank journal, and the center-tocenter length has very little effect on the engine's power production. Much has been written about the importance of longer-than-stock connecting rods how they have a better rod angle, produce less piston skirt loading, have more "dwell time" at top dead center (TDC), and the importance of the rod-to-stroke ratio. Balderdash. I can hear your teeth gnashing now. Good. Let's try some new ideas.

The reason tall-deck blocks and long rods are needed with long-stroke engines has little to do with the piston/rod angle after TDC, and a lot to do with how far the piston skirt extends below the bore at BDC. The more the piston sticks out the bottom of the bore, the less stable it becomes, which not only affects ring seal but also increases piston skirt wear. These long rods (6.800 inches) provide pistonskirt- to-crank-counterweight clearance with this 4.500-inch-stroke crank in a talldeck (11.200 inches) block.

This +.400-inch Manley H-beam 4340 steel rod is typical of the high-quality aftermarket rods that are readily available in a variety of lengths for the big-block Chevy. They are nominally rated to 900 hp, but routinely end up in engines making in excess of 1,000 hp with no problems.

To get rod center-to-center length, just measure the beam section and add 1/2 of the pin bore diameter and 1/2 of the big-end diameter. Standard pin bores are .990 inch and the big end should be 2.324 inches. Add them and divide by two to get 1.657 inches. Stock Chevy rod length is 6.135 inches, so 6.135 – 1.657 = 4.478 inches. This beam section measures 4.878 inches, so this is a "+.400-inch" rod.

First, I use longer-than-stock rods in all of my racing engines, but not for any of the reasons listed above. Remember, your primary goal with the rotating assembly is to make it as light as possible, while still retaining adequate strength to do the job. And longer rods lead to shorter pistons that weigh less than the tall pistons used with short rods. As much as I'd like to take credit for coming up with this radical anti-establishment statement, I can't. The credit belongs to noted Chevrolet engine builder and Pro Stock pioneer David Reher, of Reher-Morrison Racing Engines. Author of many technical articles on bigblock Chevy racing engines. Here's what David has to say on the subject:

"Many books and technical articles have been written concerning the supposed importance of connecting rod length to racing engine performance. Rod length actually has very little impact on power output. Choose your crankshaft and pistons first; they dictate the rod length you need.

"Conventional racing engine theory states that long-rod engines have significantly different torque and horsepower profiles than do short-rod engines. The theory is that the rod length affects the position and speed of the piston. Statements are often made that the piston lingers (dwells) near TDC on a long-rod engine and that this affects breathing. This turns out to be largely untrue.

"At 10-degree ATDC (the time when the most pressure is present in the cylinder on a power stroke), the difference in piston location between the longest (6.535 inches) and shortest (6.135 inches) rod engines is only .0004 inch. Even at 45 degrees of crank rotation, the difference is only .010 inch. This amounts to only .16 ci per cylinder in a 502-ci engine. Rod length and angularity have very little real impact on engine performance.

" Bearings

Automotive engines use plain bearings, which are sized so precisely to the crankshaft journals that they literally float the crank and rods on a hydrodynamic wedge of oil supplied by the oil pump. What we gearheads call bearings are really bearing inserts, which can easily be changed when worn and sized to accommodate changes in the crankshaft; for instance, when the crank journals are ground undersize.

Most bearings feature a tri-metal design: a hard steel backing to retain the shape, a layer of copper for thermal conductivity, and a layer of soft Babbitt that can embed small particles without damaging the crank journals. Some performance engine bearings offer an additional coating of some type of polymer or Teflon for even greater friction reduction.

Chevy engine bearings are split into two halves that get clamped together when you tighten the main caps in the block (main bearings) or the connecting rod cap (rod bearings). The bearings are slightly larger than the bore so that they are securely clamped when you tighten the caps. This is called bearing crush, and is one of the reasons that bearings are thinner at the ends. Another reason is that the high loads in a performance engine tend to elongate the opening in the bearing bore, and this action pulls the sides of the bearing inward. Consequently, when you measure bearing diameter and clearance, always measure at a point 90 degrees from the parting line.

When measuring bearing clearance, always measure at a point 90 degrees from the parting line.

Chevy main bearings have an oil hole and groove in one half, and this half always goes in the block and aligns with the oil supply hole.

Locating tabs align the bearing inserts with matching notches in the block and the rods. Chevy main bearings have an oil hole and groove in one half, and this half always goes in the block and aligns with the oil supply hole. The bearing insert in the main caps has no oil hole or grooves. In the past, some thought that grooving the bearings all the way around (360 degrees) ensured more oil supply to the main journals, but that has since proven to be faulty logic. Such a bearing only lessens the load-carrying ability of the oil wedge, and should never be used. Connecting rod bearings are the same for the upper (beam section) and the lower (rod cap), except that aluminum connecting rods require a hole in the cap bearing for a locating dowel. Because of aluminum's high thermal expansion rate, the dowel prevents the bearing from spinning in the bore, which destroys the engine in short order.

Most performance bearings are slightly narrower than passenger car bearings to provide needed clearance with the larger fillet radius in a high-performance crankshaft. Bearing inserts are available in many sizes, usually standard (OEM spec), and undersizes of .001, .010, .020, .030, and .040 inch. Custom cranks may require entirely different bearings; for instance, many big-block cranks are offered with small-block Chevy rod journals of either 2.100 or 2.000 inches. Pro Stock engines use Honda rod bearings measuring 1.889 inches (48 mm) and 2.500-inch main bearings from a 409 Chevy.

Stock big-block bearing specs call for clearances of .002 to .0025 inch, but most performance engine builders prefer slightly larger clearances of .003 to .004 inch. This is one of the reasons that most performance big-blocks are equipped with high-volume oil pumps, because larger clearances result in more internal oil leakage.

Pistons

Although those shiny new pistons are well hidden inside your big-block, their importance in the engine's power production is paramount. Remember that other modifications (such as a bigger cam, aluminum heads and intake manifold, exhaust headers, double throwdown carburetor, and flame-thrower ignition) are of little or no value if they don't lead to higher pressure on the piston during the power stroke. The piston, ring, and cylinder wall must all work together to harness the energy of combustion, letting as little as possible escape in the form of blow-by (gas leakage past the rings) and frictional losses.

The piston design can also be a source of additional power through higher compression ratios, which extract more thermal energy from each drop of fuel, but there are limits to how much can be gained with a particular type of fuel. An engine with a 14:1 compression ratio makes more power than the same engine with 9.5:1 compression, if the fuel has a high enough octane rating to prevent pre-ignition and detonation; that means race gas. But for street use, 92-octane premium pump gas generally does not tolerate more than a 9.5:1 compression ratio (higher with aluminum heads and other "tricks"). The first general rule here is to go for all the compression you can get within the boundaries of the fuel you use. More compression is as close as you can get to "free" horsepower in an internal combustion engine.

Big-block Chevy pistons are either cast or forged aluminum. Most production engines were equipped with cast pistons, which are actually an aluminum casting over a steel strut, which serves to strengthen the relatively weak cast part. The biggest advantage of cast pistons is that they expand less than forged pistons when hot, so they may be fitted to the bores with less piston-to-wall clearance. This offers the benefit of less noise and piston clatter upon start-up, and very good ring seal and longevity because tighter clearances mean less piston rock in the cylinder bore.

A variant of cast pistons are hypereutectic pistons, which are cast from an aluminum alloy containing more silicon than traditional cast pistons. They also can be fitted tightly to the bore, with typical piston-to-wall clearances of .002 inch. They are stronger than regular cast pistons, but still do not provide the extreme strength of forged pistons, and should not be used in racing big-blocks or with more than a small amount of nitrous, typically up to 150 hp.

Forged aluminum pistons are the best choice for any serious performance engine, and all of Chevy's potent factory high-performance engines came with forged pistons. Even within the forged piston ranks, different aluminum alloys are used depending on the application. Most high-performance street and moderate strip engines are best served with

pistons forged from 4032 aluminum, a high-silicon alloy providing good lubricity and less expansion due to heat. Typical piston-to-wall clearance with 4032 is .0045 to .006 inch. For supercharged, heavy nitrous, or all-out racing applications, most manufacturers use 2618 aluminum for its tremendous strength and durability under high-heat/high-load conditions.

However, the downside is that pistonto- wall clearances must be opened up to .0065 to .008 inch due to its higher thermal growth rate. Careful warmups are definitely called for before any full-throttle loads are put on the engine because the pistons are quite loose until operating temps are realized, and excessive blow-by and oil consumption may result as the cold piston/ring package rattles around the bore.

Like most other performance parts for the big-block Chevy, we enjoy an almost embarrassing number of good aftermarket piston manufacturers that can supply pistons for virtually any bore, stroke, rod length (compression height of the piston), dome shape and volume, valve reliefs, and ring package you can imagine. You may choose from a dizzying array of stock replacement or custom pistons from Arias, BRC, Diamond, Federal-Mogul/Speed-Pro/Sealed Power, JE, Keith Black/Silv-O-Lite, Probe, Ross, Venolia, Wiseco, and others.

Most OEM pistons are cast aluminum, like this Silv-0-Lite stock replacement 427 piston. The offset pin location reduces piston "slap" and results in quieter engine operation. With a .140-inch dome, it makes 9.5:1 compression with closed-chamber heads and accepts stock spec 5/64-inch top rings and 3/16-inch oil rings.

This KB Performance hypereutectic piston for a 454 big-block has a net dome volume of 12 cc. Because piston-to-wall clearance is so tight (.002 inch), it offers a very stable platform for excellent ring seal and long life in a street Rat motor. Compression is 9.1:1 with 119-cc open combustion chambers, and 9.9:1 with 108-cc closed chamber heads.

JE SRP 4032 forged aluminum piston with a high-compression dome for open chamber heads has 1/16-inch top rings and a 3/16-inch oil ring. Note oil drainback holes in oil ring groove. Piston diameter should be measured 1 inch up from bottom of the skirt, perpendicular to the pin bore.

Some piston manufacturers offer the option of digitizing your cylinder head combustion chambers and machining the piston domes to match perfectly, with the valve reliefs in exactly the correct position, angle, and depth to match your heads. This JE Pistons engineer is designing a custom big-block piston using sophisticated computer-aided design and manufacturing software.

This JE piston has a CNC-machined max piston dome to match Edelbrock Victor 24-degree heads. Note lateral gas ports in the top ring groove, and accumulator groove between the top and second ring grooves. An oil ring support rail is used where the oil ring intersects the pin bore.

As supplied by the piston manufacturer, piston domes may have sharp edges from the many machining operations; these cause hot spots, which can cause pre-ignition. These should be smoothed by hand, removing as little material as possible to retain compression.

Piston Rings

The most important function of the piston is to provide a stable platform for the rings to achieve the best possible seal with the cylinder bore. Careful attention to the ring selection, cylinder bore preparation, and ring fit inside the piston ring grooves is just as important to your highperformance engine as the latest camshaft, carburetor, or cylinder head.

Modern pistons for the big-block have three rings; a top compression ring, a second compression ring, and an oil control ring, which is really an assembly of two steel rails and a wavy spacer designed to scrape excess oil from the cylinder walls on the down stroke. Ring material is usually cast iron, ductile iron, or steel, and high-performance rings typically have a plasma-molybdenum face for better sealing and reduced friction with the cylinder walls. Chrome rings are available for engines that are subjected to dirty operating conditions, such as off-road racing, but they require a different cylinder wall finish and do not conform to the cylinder bore as well as high-performance rings. Low-tension oil rings are popular to reduce ring drag, but should only be used if the engine has some type of crankcase pressure reduction system such as a vacuum pump, dry sump oil pump, or pan evacuation system in the headers.

A typical ring package for highperformance pistons would include 1/16-inch top and second rings with a 3/16-inch low-tension oil control ring. This set has a barrel-face moly top ring, tapered cast-iron second ring, and threepiece oil ring assembly consisting of two steel rails and a wavy steel expander. Most engine builders order rings that are .005-inch over the finished bore size, then file fit each ring to a specific end gap for reduced blow-by.

Cross-sections of typical high-performance and racing ring designs. Gapless top or second rings feature a steel rail under the main ring section, which closes off the end gap for greatly reduced blow-by and more power. (Illustration Courtesy Total Seal)

Piston ring-to-groove clearance is just as important as piston-to-wall clearance for maximum power. The correct clearance lets combustion gases behind the ring push it tighter into the cylinder bore for a better seal. Many competition pistons have gas ports drilled into the top ring land for the same effect, only more so. Back clearance is necessary to prevent rings from bottoming in the groove and to provide the needed volume for combustion gases to pressurize the ring. Some manufacturers offer back-cut rings to fit in a shallower ring groove, which may be necessary with very high ring locations and deep valve relief notches. (Illustration Courtesy Total Seal)

It's easy to check ring back clearance by rolling the ring around the groove. Note the vertical gas ports drilled in the piston top, which intersect the back of the top ring groove.

With a long stroke and/or long connecting rods, it's common for the pin bore to intersect the oil ring groove. JE supplies a support rail to span the gap and support the oil ring. The support rail's radial tension pulls it in toward the piston, while the oil ring rails are designed to push out against the cylinder wall for a better ring seal. Note the locating dimple on the bottom of the rail, which must be positioned in the pin bore gap.

Stock cast aluminum big-block pistons are machined for rings that measure 5/64, 5/64, and 3/16 inch (oil ring). They are typically made from cast iron. Nearly all high-performance pistons for the street and modest racing applications use 1/16-, 1/16-, and 3/16-inch rings. Narrower rings have less mass than the fatties, and are able to maintain a good seal in the ring groove without fluttering at high engine speeds. High-end racing engines often use top rings measuring .043 inch, and Pro Stockers may use rings as thin as .7 mm (.0275 inch) with 3-mm (.118-inch) oil rings. As with everything, there is a trade-off. Narrow rings cannot handle as much heat as thick rings, and they wear out quicker.

Obviously your ring choice is influenced by your application; you don't use the same rings in a street engine that you hope can survive for 100,000 miles as you use in an 8,000-rpm race Rat.

All GMPP 502-ci crate engines use a unique ring package measuring 2, 1.5, and 4 mm (oil ring). The production 4-mm oil ring is a low-drag version that may cause excessive oil consumption in some applications. If you are re-ringing the original pistons and are not using some sort of crankcase evacuation system, it is a good idea to replace it with a conventional 4-mm oil ring. There are many top ring face designs, but the most popular for performance is the barrel-face plasma-moly. Dykes top rings have an L-shaped cross-section that uses combustion pressure to seal tightly against the cylinder walls, although most Rat racers these days accomplish the same thing by using traditional rings with gas ports in the piston to pressurize the back side of the ring. Second rings may have a reverse taper or Napier design, which has an undercut to reduce the width of the tapered face to aid in scraping oil off the cylinder wall on the down stroke.

Harmonic Dampeners

That big chunk of metal on the front of your crankshaft serves a much more important function than just a place to bolt on the front pulley. Sometimes called a harmonic balancer, or just balancer, its real function is to dampen harmonic vibrations from the crankshaft. Without one, or with one that is not matched to your engine, the crankshaft eventually develops cracks and fails.

Big-block dampeners fall into two categories: internally balanced or externally balanced. All 3.76-inch-stroke engines (396, 402, and 427) came with an internally balanced dampener, and 4.000-inch-stroke engines (454 and 502) came with externally balanced dampeners. Stock harmonic dampeners were available in 7- and 8-inch diameters. If you look closely, you see that the dampener is actually two pieces of metal—a center hub that bolts to the crank and an external metal ring that is bonded to the hub with rubber. That is why you must use the proper dampener installation and puller tools for removal and installation. If you were to use a common gear puller, you would pull the outer ring off the hub and destroy the unit. Likewise, installation should never be done by hammering on the dampener as that also destroys the bond between the two parts. Stock dampeners are subject to deterioration of the rubber bond, which leads to inaccuracies when setting the ignition timing if the outer ring has shifted its position.

This stock externally balanced 454 harmonic dampener has a large counterbalance weight on the back side.

Fluidampr's CT Gold dampeners use centering technology to improve the control of torsional vibrations above 6,000 rpm. Targeted at drag race big-blocks, this new technology allows the inertia ring to remain centered in the housing cavity, even when the unit is at rest. This one has a counterbalance weight for use with 454/502 externally balanced engines. (Photo Courtesy Fluidampr)

GMPP's harmonic dampener PN 12361146 is standard equipment on the 572-ci crate engines. This 8-inch-diameter internally balanced dampener is SFI-certified and works on any neutral-balance engine. (Photo Courtesy GMPP)

The Rattler by TCI takes a unique approach to vibration control. Pendulum weights inside the dampener are designed to move to counteract the crankshaft harmonics. The principle is similar to a deadblow hammer, which uses moveable shot to prevent bounce-back. (Photo Courtesy TCI)

Exploded view of ATI's Super Damper shows the internal inertia weight with tunable O-rings for specific engine combinations. The outer shell bolts solidly to the hub so there is no chance of the timing marks shifting position, which is a common failure of stock harmonic dampeners. (Photo Courtesy ATI)

ATI Super Damper being installed on an all aluminum big-block racing engine. Always use the correct damper installation tool; never hammer on the damper.

All high-performance and racing big-blocks should be equipped with an aftermarket harmonic dampener that is designed to control these damaging harmonic vibrations much better than the stock units. If you are going take your car to the dragstrip, an SFI-approved dampener is mandatory for cars running quicker than 10.0 seconds in the quartermile. Even if your car isn't that quick, the benefits of longer crank and internal parts life is worth the investment. Note that GM's big-boy 572-ci crate engines come with an SFI dampener (PN 88962814), which is available through GM Performance Parts. This is an internally balanced dampener, and works well on any 396-, 402-, or 427-cube motor as well.

While there are SFI-certified externally balanced dampeners, most racing engine builders prefer to have the crankshaft internally balanced by adding heavy metal to the crank counterweights during the engine balancing operation. This likely adds several hundred dollars to the cost of balancing, but the results are a much more balanced and stable rotating assembly. Of course, the flywheel or flexplate must also match the crank and dampener combo, whether internally or externally balanced.

Aftermarket dampeners use various methods to control harmonic vibration. Many refine the OEM elastomer-to-metal bonding technique to prevent deterioration of the bond, but Fluidampr uses an inertia weight dampened with viscous fluid inside a sealed unit to control engine harmonics. Another approach is taken by the TCI Rattler, which has internal pendulum rollers that move to counteract crankshaft vibration in a running engine. All SFI-certified dampeners have passed stringent tests to ensure safe operation at high engine speeds, and may be relied upon to deliver excellent performance.

Aftermarket harmonic dampeners are available in 6-, 7-, and 8-inch diameters (approximately) to satisfy the requirements of different big-block engine combinations. In general, the larger dampeners are needed with long strokes, and the smaller dampeners allow a competition engine to rev quicker. Most are all steel, but some are available with aluminum components to reduce weight, again for quicker acceleration. Before you automatically go for the smallest, lightest dampener to get your hot rod down the racetrack quicker, remember that the dampener's most important function is to reduce damaging crankshaft harmonics and improve the lifespan of your engine. Check with the manufacturer for specific recommendations, and you and your crankshaft will both be happy.

Flywheels and Flexplates

Big-block Chevy flywheels are available in two diameters, 14 and 12.75 inches, although the vast majority use the larger 168-tooth size. Flexplates, socalled because they allow the torque converter a small amount of flex to properly center itself on the transmission input shaft, are only available in the larger 168-tooth configuration. Bigblock flywheels and flexplates are either neutral balance for use with 396-, 402-, and 427-ci engines, or have external balance weights for use with 454- and 502-ci engines. Engines with one-piece crankshaft seals require externally balanced flywheels or flexplates (except for GMPP ZZ427, ZZ572/620, ZZ572/720R, and the Anniversary Edition 427).

Check the charts below to find the correct GM parts for specific engine applications.

Stock 454 flexplate has a large counterbalance weight next to the starter ring gear. This externally balanced flexplate must be used with matching harmonic damper and externally balanced crank (454 and 502).

Meziere billet steel flexplate is machined from solid 4340 steel for maximum strength with minimum runout. They are available with standard 12-pitch gears (168-tooth), or new 10-pitch tooth design with 139 teeth, which must be used with a matching 10-pitch starter. (Photo Courtesy Meziere Enterprises)

GMPP flexplate PN 12561217 is .100 inch thick for internally balanced engines. (Photo Courtesy GMPP)

GMPP flywheel P/N 14096987 is lightweight nodular iron for externally balanced engines. (Photo Courtesy GMPP)

An SFI-certified scattershield like this Lakewood PN 15000 is required for any car running quicker than 11.50 in the quarter-mile, and it's a good investment for any standard transmission-equipped high-performance big-block car. (Photo Courtesy Lakewood)

An SFI-certified flywheel, like this Hayes 153-tooth steel flywheel, is also required for any car running quicker than 11.50 in the quarter-mile. (Photo Courtesy Hayes)

Flexplates are thinner than flywheels and require different-length bolts. Stock flexplate bolts PN 3727207 (six required) are 7/16-20 x 27/32 inch, and flywheel bolts PN 12337973 (six required) are 1.0 inch long. High-performance and racing big-blocks put a tremendous load on these six fasteners and it's always a good idea to upgrade to specialty aftermarket flywheel or flexplate bolts, such as those offered by ARP. A flywheel dowel (GM PN 10046031, 7/16-inch OD x 7/8-inch long) is also a good idea with any highoutput Rat motor.

Remember that these are original equipment flywheels and flexplates, and do not meet SFI specs required by most race sanctioning bodies. I urge you to equip your big-block with a high-quality aftermarket flywheel or flexplate meeting SFI specs. Those parts have been tested and approved for high-RPM use and are not likely to disintegrate with catastrophic results. If you have a Gen V or Gen VI engine, note that cast crank and forged crank engines require different flywheels or flexplates. When switching to an aftermarket wheel on Gen V/ VI engines, you need to have the crank balanced with the new flywheel and harmonic dampener.

Starters

Stock starters are fine for stock engines, but high-compression and largedisplacement Rat motors need all the cranking power they can get.

There are two basic OEM starter designs for the big-block that must be used with the matching 123⁄4- or 14-inch flywheels/flexplates. All generations of big-blocks use the same 3 x 3/8-16 bolthole pattern on the right side of the engine to accommodate either starter design. The majority of Rat motors are equipped with a 14-inch (168-tooth) flexplate, and the OE starter design uses the two staggered bolt-holes for mounting. The 123⁄4-inch flywheels had 153 teeth, and starters for these engines used the two bolt-holes perpendicular to the crank centerline in the block. There were no 123⁄4-inch (153 tooth) flexplates produced by Chevrolet, so these starters would only be used on vehicles equipped with standard transmissions. Production starters are adequate for most streetable big-blocks with up to 10.5:1 compression, but high-compression and largecubic- inch motors need a high-torque aftermarket starter.

This hightorque Super Mini Starter from East Coast Auto Electric features a gearreduction 2.4-hp motor, and the body can be clocked to provide extra clearance for your particular oil pan or headers. The dual mounting pattern works with either 123⁄4 – or 14-inch flexplates. Chrome doesn't make your car any faster, but it sure looks good!

GM Performance Parts offers this ministarter (PN 12361146) that weighs only 10.5 pounds and has a 3.75:1 gear reduction ratio. It works with both 123⁄4– and 14-inch flywheels or flexplates and includes mounting bolts, shims, gaskets, and electrical connectors. (Photo Courtesy GMPP)

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Meziere starter features 2.2 kilowatts of cranking power and is available with standard 12-pitch or larger 10-pitch gear for mountain motors with very high compression ratios. The 10-pitch starters must be used with matching 10-pitch flexplates. (Photo Courtesy Meziere Enterprises)

Most big-blocks produced before 1975 used ignition distributors with points, and those starters include an "R" terminal (the small terminal on the left) to by-pass the ballast resistor for more voltage to the spark plugs while cranking the engine. If you have an electronic distributor, including the HEI, this terminal is not needed. Most aftermarket starters do not have this provision, since modern engines all use electronic ignition systems.

GMPP starter PN 10465143 is a lightweight starter suitable for streetperformance big-blocks with a 153-tooth flywheel. Originally for 1993–1997 Camaros and Firebirds with the LT1 engine, the bolt pattern is inline and must be used with starter bolts PN 14097279 (1) and P/N 14097278 (1). (Photo Courtesy GMPP)

OE starter bolts are knurled to accurately locate the starter and must be used to prevent damage or failure of the starter and/or ring gear on the flywheel.

A starter heat shield like this one from Moroso helps prevent heat soak. This unit fits stock Delco starters, but they are also available for most aftermarket starters. (Photo Courtesy Moroso)

Full-size OEM-type starters use an engine brace to support the front of the starter, while the lighter mini-starters don't require a brace. Heat shields are available from many sources and may be constructed from sheet metal or some type of protective high-heat blanket.

The use of 16-volt batteries is common in racing applications, and this presents no problem to the starter. The extra kick from a 16-volt system results in a quicker start-up, so that the starter is actually working less than with a 12-volt system. There are even aftermarket starters wired for 24 volts that must be used with dual 12-volt batteries.

Project: Balancing the Reciprocating Assembly

Each end of the connecting rods must be balanced separately. This machine supports one end at a time (the small end in this case). Then the seven heavy rods have metal removed to match the lightest rod. Most aftermarket connecting rods come pre-balanced, but your engine balancer checks them to be sure.

Some of the aluminum is removed from the piston skirts with a milling to reduce weight and equalize all eight pistons.

After all eight pistons and rods are balanced to each other, a formula is used to determine the weight of bob weights that get clamped to the crank rod journals. Modern crank balancing machines, like this one at Scat, digitally measure and display imbalance after spinning the crank so that the operator knows how much metal needs to be removed from the counterweights with the drill press. The operation is repeated until everything is spot on.

This 5-inch-stroke mountain motor crank had to have lots of heavymetal slugs added to achieve a neutral balance. Most 4- or 4.250-inch cranks just need one or two.