A crankshaft transfers the energy created during combustion into a rotating force that’s channeled through a transmission and rear axle, and finally to the tires for vehicle motivation. As each cylinder fires, the crankshaft must be rigid enough to endure the shock loads associated with combustion, but flexible enough to not fatigue and fail at any reasonable engine speed. It’s a delicate balance that requires precise balancing and exact tuning to prevent premature failure.
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Original Pontiac Cranks
When Pontiac developed its V-8, the crankshaft was engineered to provide a long and reliable service life. It’s supported by five large main journals and uses large counterweights to maintain centrifugal balance and motion during normal operation. The design features large bearing surfaces and a considerable amount of overlap between the main and rod journals to increase rigidity. Forward/ rearward thrust is taken up at the fourth main journal.
Enlarging bore diameter and adding crankshaft stroke length were ways that Pontiac increased the displacement of its original 287 to an eventual size of 455. Main journal size initially measured 2.5 inches, but to maintain sufficient journal overlap for maximum rigidity as stroke lengthened, it increased to as much as 3.25 in later years. The crank pin, or connecting rod journal, as it’s often called, remained at 2.25 inches throughout the entire production run. Pontiac cranks are generally categorized and referred to by main journal sizing. The 3-inch unit was used in all V-8s up to 400 inches produced between 1959 and 1979. The 3.25-inch unit was introduced in the early 1960s for the 421, and is found in all other Pontiac engines displacing up to 455 ci. Generally speaking, cranks with the same main journal sizing freely interchange, but there are some slight differences that can affect it (covered later in this chapter).
All Pontiac cranks produced though 1958 were constructed of forged steel. Though quite durable, they’re of no real use to performance enthusiasts today because the main journals measure less than 3 inches. Bearing spacers that allow the use of such cranks in 389 and 400 blocks were once available from a few sources, and can still be made by most competent machine shops. With so many drop-in forged-steel cranks available today, however, there’s less of a need to use an original forging. Once Pontiac increased main journal diameter to 3 inches, it found that a cast crank could offer sufficient durability and reliability for its production V-8, allowing the elimination of the costly forging in all but a limited number of highly specialized competition engines. Pontiac began casting its production cranks in 1959. It used pearlitic malleable iron (PMI), Armasteel, or nodular iron, depending upon the model year and application. The castings proved to be very rigid and resisted flexing.
Despite the material it’s constructed of, the stock castings contain about the same tensile strength. Those constructed of Armasteel, a GM trade name for a specific iron alloy that exhibits some steellike qualities has the highest, but only by a slight margin. The nodular iron unit was used in most every Pontiac engine during the years when production peaked. Such cranks are definitely the most common and are nearly as durable as any Armasteel unit. A nodular iron casting is identifiable by a large “N” on or near the first counterweight.
Selecting a Stock Crank
If considering an original Pontiac crankshaft, I suggest any Armasteel or nodular iron casting produced from 1964 to about 1974, so long as it contains the appropriate stroke and journal dimensions for your application. These castings generally weigh between 60 to 70 pounds and are adequate up to 600 hp. Some push that toward 700 hp or slightly more, but it requires proper preparation and machining and precise tuning to survive reliably at that level.
Castings produced prior to 1964 are about as durable as later castings, but snout length is generally shorter, and the flywheel flange bolt pattern is different. That can present installation issues and/ or require other corresponding parts such as the timing cover or flywheel/flexplate. The block may require minor grinding to achieve sufficient clearance when combining certain cranks and blocks. The crank counterweights or rod throws can contact the bottom of the cylinder bore at certain points during rotation. I highly recommend test fitting the components anytime a block and crank are not matched originals.
In an attempt to shed engine weight and improve fuel economy during the mid 1970s, Pontiac lightened its V-8 crankshaft of the era as well. The casting isn’t quite as robust as earlier examples. Such castings can be identified by the part number, which can be fully cast, partially cast and partially stamped, or fully stamped on the front counterweights. While completely adequate for engines producing up to 500 hp or so, an earlier Armasteel or nodular iron crank is a better option when pushing horsepower beyond that.
The highly specialized 1960s Super Duty and tunnel-port Ram Air engines were equipped with high-quality, forged-steel crankshafts for maximum durability and reliability. The factory forgings can be identified by a very wide parting line that runs parallel to the crank centerline, and further identified by its part number. Production was very limited. They remain extremely rare and are quite valuable. Unless you have an original engine that requires such a crank, I recommend leaving them to the restorers. Modern forgings are a better value.
Original Crank Modifications
A crankshaft constantly flexes during normal operation. Over time, cracks can develop in the fillet area (where the journals meet the counterweights). If your build includes a cast Pontiac crankshaft, it must be magnetically inspected (Magnafluxed) to determine that it’s completely crack free before spending any money on machining. You’re much better off spending a few bucks to ensure a crank you already purchased is usable and throwing it away than chancing the entire engine should it fail.
Pontiac used excellent materials and precision casting and machining techniques when producing its cast cranks. That and the use of quality bearings negated the need to artificially harden the journal surfaces to improve durability. It also eliminated the risk of removing that hardening when undersizing the journals during routine machining. About as much as .050 inch can be removed without compromising crankshaft rigidity. The limiting factor is availability of correctly undersized bearings.
Beyond normal grinding and micropolishing of the journal surfaces, there isn’t much more that a cast Pontiac crank requires for use up to 600 hp, or slightly more. I suggest removing all traces of casting flash from the counterweights to eliminate areas where cracks can propagate. Other modifications such as lightening or narrowing the counterweight’s leading edge can increase engine acceleration rate, but may not improve actual performance in all instances and, as such, is not always cost effective.
The main journal oiling passages on a stock 3.25-inch Pontiac crank are drilled completely through for maximum rodbearing lubrication. Those on a 3-inch crank are drilled only partially through. Drilling completely through the journal of a 3-inch crank can increase the amount of oil connecting rods see during each complete rotation. While there aren’t any real negatives to cross drilling a stock crank, it isn’t always required with modern main bearings. Chamfering the lubrication passages that intersect the journal surfaces removes burrs and better disperses oil over a greater area of the bearing surface.
If the journals of a stock cast crank require resizing to a dimension that exceeds modern bearing undersize availability, some specialty shops claim the crank can be salvaged by restoring the thickness of the journal surface with spray welding. I strongly recommend against this for any high-performance engine,as any attempt to weld new material onto an existing cast surface can ultimately lead to cracking. If appropriately undersized bearings are unavailable, it’s best to simply start with another crankshaft.
Pontiac did not use nitride or cryogenic treatments or hard chroming to harden its crankshaft journal surfaces. Such treatments, however, can benefit modern applications where extreme conditions and harder bearings can damage the journals. While such treatments may possess no negative effects in any rebuild, it certainly doesn’t fit every budget.
Adding displacement is an easy and effective way to improve engine output. In addition to enlarging bore diameter over the years, Pontiac often lengthened V-8 crankshaft stroke to accomplish exactly that. The additional stroke length creates more leverage on the crankshaft, which generally increases the amount of available torque, particularly at relatively low RPM, making it ideal for engines that are primarily street driven.
If you’ve ever driven a vintage Pontiac with a stock 400 and another with a stock 455, you likely recognized that the 455 felt more powerful, especially in its ability to spin the tires from a standing start. Though the two engines have nearly similar bore diameters at 4.12 and 4.15 inches, respectively, the additional torque the 455 generates is directly related to crankshaft stroke length, which is nearly 1/2 inch longer than that of the 400. Whether or not the 455 creates more high-RPM horsepower than the 400 depends upon many other factors.
The generous amount of journal overlap that Pontiac designed into its crankshaft allows a slight stroke length increase without grossly affecting the rigidity of a stock casting. The “stroking” process is quite involved and requires resizing the rod journals from the stock Pontiac diameter of 2.249 to 2.2 inches, a measurement that’s common to the bigblock Chevy. The rod journal axis is then relocated with offset-machining, which effectively increases stroke lengthen by .040 to .050 inch, adding another 6 to 8 ci of total engine displacement.
In addition to a slight displacement boost, greater stroke length increases the amount of time that a piston remains stationary at the top and bottom of the cylinder as the crankshaft changes direction. That “dwell” allows the piston to accelerate slower from a stop, which gives the engine more time to better fill and evacuate the cylinders. It also gives the pressure generated during combustion more time to exert its force on the piston, which promotes maximum torque. It can, however, induce enginedamaging detonation if the engine is already running on the edge for the fuel octane being used.
Extended piston dwell does present some negatives. Even though the piston accelerates slower, it actually reaches a higher terminal speed as it has a greater distance to travel during each rotation. That and the additional side loading associated with the longer stroke translate into greater friction and stress exerted on the block and its cylinder walls. A longerthan- stock connecting rod (to improve rod-to-stroke ratio) can alleviate some of that, but a rod that’s too long requires a piston with a very short compression height, and that can lead to its own set of issues.
With a number of new crankshafts being produced for the Pontiac V-8 in recent years, manufacturers began offering Pontiac cranks with a wide array of journal and stroke combinations. That includes stock dimensions for use as new OE replacements, and specialized units that feature stock journal main sizes but with much greater stroke lengths. The advent of the readymade “stroker crankshaft” allows any hobbyist to easily transform a 400 into a 461- to 467-inch engine at a very reasonable price, and it’s an immensely popular modification.
Eagle Specialty Products introduced a new Pontiac V-8 crankshaft casting in 2001. It provided an alternative to using a questionable original, or where journal undersize requirements exceeded available bearing options. Other companies have introduced similar castings in recent years, and while some are of questionable quality, I am comfortable recommending cast crankshafts from a few of them.
When the carbon content of iron reaches 6 percent, an alloy becomes steel in a technical sense. For its cast cranks, Eagle uses nodular iron with a high carbon content that can be classified as steel. Eagle’s cranks are produced at its own Chinabased production facility and are held to a strict tolerance. While some isolated thrust surface issues were reported early on, today the Eagle casting is known for its consistency and reliability. I consider it an excellent choice whenever a stock nodular iron crankshaft is considered.
Weighing about 70 pounds, Eagle’s cast crank is available with 3-inch main journals and 4.25-inch stroke. A 3.25- inch main journal unit is available with stroke lengths of 4.21 and 4.25 inches. The 4.21-inch unit uses stock-type connecting rods while the 4.25-inch units use longer big-block Chevy type of rods, such as those measuring 6.7 and 6.8 inches. Eagle’s recommended horsepower limit for its cast Pontiac crank is 700 hp.
Ohio Crankshaft began offering cast-iron Pontiac V-8 crankshafts within the past several years. The castings are constructed of nodular iron and weigh about 70 pounds. I have found excellent fit and function. Cast cranks with stock Pontiac rod journals are available with 3- and 3.25-inch main journals, and with 4- and 4.21-inch stroke lengths. A stroke length of 4.25 inches is only available with 2.2-inch rod journals. A cast crank from Ohio sells for less than $300 and can be considered another excellent choice for engines producing as much as 600 hp.
When an engine exceeds 550 hp or 6,000 rpm, or when forced induction or nitrous oxide is used, a forged crank is a very worthwhile investment. A cast crank can flex at very high RPM and/or in high-horsepower applications, causing premature bearing wear, especially when using a unit with 3-inch main journals, and a stroke length of 4.21 inches or more. A forged-steel crankshaft is generally more resilient to flexibility and fatigue and can sustain 1,000 to 1,200 hp for only a few hundred dollars more than the cost of a cast crank. Even if you don’t expect to ever reach that performance level, a forging allows for significant power increases in the future without creating reliability concerns. Replacing a cast crank with a forged unit in an otherwise good-running engine can be a costly and time-consuming endeavor! There are a few excellent choices readily available that I am confident to recommend.
Eagle introduced its forged 4340- alloy crankshaft in 2009. Selling for around $800, it’s an affordable option that offers the durability required for high-performance use. A fully-machined forging weighs about 75 pounds and includes cross-drilled main journals for maximum oiling. For blocks with 3-inch main journals, Eagle offers stroke lengths ranging from 4.21 to 4.5 inches. The 4.21- inch unit features 2.25-inch rod journals while others have 2.2-inch journals. Forgings with 3.25-inch main journals are available with 4.21- and 4.25-inch stroke lengths only.
Forged 4340-steel cranks from Ohio Crankshaft are available with 3- and 3.25-inch main journals. The 3-inch unit features cross-drilled main journals and are available in a variety of stroke lengths ranging from 3.75 to 4.75 inches with Pontiac- and Chevy-size rod journals. The 3.25-inch forgings with stock-dimension rod journals are available with 4- and 4.21-inch stroke lengths, and 4.25- and 4.5-inch stroke lengths with 2.2-inch journals. Weighing around 75 pounds, Ohio Crankshaft claims its forging can sustain as much as 1,500 hp. With a cost around $600, it’s an excellent value.
Scat Crankshafts offers a variety of forged 4340-steel crankshafts with 3- and 3.25-inch main journals in stroke lengths of 4, 4.25, and 4.5 inches. Its cranks are only available with 2.2-inch rod journals and come in three different weight variations, which are accomplished with counterweight profiling. Its Standard crank weighs about 75 pounds, while the Lightweight and Super Lightweight cranks weigh about 65 and 60 pounds, respectively. Costs range from $850 for a Standard unit to $1,525 for a Super Lightweight forging.
RPM Industries and Star Galaxy also offer cast-iron and forged-steel crankshafts for the Pontiac V-8. A variety of main and rod journal and stroke length combinations are available. I understand the quality is generally good, but must admit that I have no direct experience with examples from either company. That doesn’t suggest that the offerings are inferior, however. I simply haven’t had the opportunity to work with them. Your Pontiac vendor should be able to comment on quality and pricing.
Many crankshaft companies also offer forged-steel connecting rods. Several have created complete rotating assembly kits that include a new cast or forged-steel crankshaft and forged-steel connecting rods and combine it with forged-aluminum pistons and the required rings and bearings to create a complete rotating assembly package. Most often the crankshaft features a stroke length of 4.25 inches, and it’s combined with connecting rods that measure 6.7 to 6.8 inches, creating a “stroker” assembly.
A stroker package is an easy way to significantly increase the displacement and output of 350- and 400-inch engines with pricing that starts at about $1,500. A typical 400 block that’s been bored .060 inch can quickly and easily displace as much as 467 ci simply by using an aftermarket crankshaft with a 4.25-inch stroke. A 455 can be made as large as 474 ci using similar equipment. Longer strokes are available and can be used, but it sometimes requires special pistons and additional block preparation such as clearance grinding, block filler, and four-bolt main caps. Your machinist or Pontiac vendor can help you decide which components are required to help you achieve your performance goals.
Specialty Billet Cranks
A crankshaft machined from a billet of 4340-steel alloy is another very durable option that’s popular with Pontiac racers. The argument of whether a billet crank is actually more durable than a forged crankshaft has raged on for many years. Ask any professional engine builder or crankshaft manufacturer and you’ll hear some very strongly supported arguments and opinions. You can decide if one is required for your application; here, I provide some comments about them that may better educate you about billet crankshafts in general.
The grain structure in a billet of highquality steel is very dense and runs in a similar plane. As the material is heat treated to a specific temper it alters the grain structure and improves strength, which further improves rigidity, reducing the amount it flexes during normal operation.
In my opinion, the main advantage of a billet-steel crankshaft is the ability to create a custom unit that fits a very specific application. A company such as Moldex can produce a very high quality crankshaft that can sustain about any amount of horsepower or RPM possible by tailoring counterweight design and other aspects for the intended application. Any combination of rod and main journal dimensions are available, as are popular features such as knife-edged counterweights and gun-drilled journals to reduce weight. Pricing from Moldex starts at $3,250 and because each crankshaft is produced on a custom-order basis, you need to allow for a lead time of 12 weeks or more.
Balancing is an important part of any engine build. It’s one that any quality machine shop should consider standard practice during a rebuild, no matter how basic. It consists of weight matching the components of the entire reciprocating assembly to a very close tolerance. While some rotating assembly kits that include a new aftermarket crankshaft are balanced by the Pontiac vendor prior to shipping, your machinist can perform the task at a reasonable cost if using outside components.
For any max-performance build, balancing should include weight matching the connecting rods, wrist pins, pistons, and even the rings. A fixture replicating the mass of those components is then bolted to the crankshaft journals, and the assembly is spun at a relatively low speed. Material is then added or removed from the crankshaft counterweights until the complete assembly is balanced accordingly. The harmonic damper and flywheel/ flexplate are often installed at some point during the process to ensure neither alters the balance unexpectedly.
Contrary to what many believe, balancing doesn’t necessarily improve engine output. It promotes maximum performance while reducing harmonic vibrations at certain engine speeds. That provides smooth and consistent engine operation at all speeds, and that can reduce complete engine wear over its lifetime, particularly to the bearings.
As a crankshaft rotates during normal operation, some pistons are forced downward by combustion, while others are pulled downward or pushed upward. Occurring hundreds of times per second, it causes the crankshaft to flex or twist, and that creates torsional vibration, which can eventually cause the crankshaft to fatigue and fail. Fastened to the front of a typical crankshaft is a hub assembly that’s designed to counteract, or absorb, the harmonic irregularities to effectively prevent crank failure over the life of an engine.
In addition to dampening harmonics, the assembly serves a second purpose for many engines of other makes. It can contain a slight imbalance, which must be factored in when balancing the entire reciprocating assembly, lending the name “harmonic balancer.” Pontiac V-8s were balanced internally, however, and though “balancer” is often used to describe a Pontiac assembly in conversation, vintage Pontiac literature refers to it as a “harmonic damper.” I will use “damper” for the sake of accuracy, but when considering a damper, it should be for an “internally balanced” engine, assuming your machinist balances your Pontiac in the traditional manner.
The inner hub slides onto the crankshaft snout. It’s keyed for positive location and retained by a large bolt and washer assembly that must be torqued to 160 ft-lbs during installation. Original Pontiac and OE-type aftermarket dampers use an outer ring, or inertia weight, that floats about the hub. It’s isolated by elastomer (rubber), which absorbs torsional irregularities, but some aftermarket units use silicone fluid. Either type can work quite well if appropriately weighted and sized for the application. The outer perimeter of most aftermarket dampers is indexed with timing marks, which provides several advantages for assembly and tuning. It can make it easier to degree a camshaft or set and/or adjust initial or total spark lead.
Pontiac dampers produced before 1968 bolt together and can be difficult to work with. The original Pontiac damper introduced in 1968 is a unitized design that measures 6-inches in diameter. It’s an excellent piece that performs very well in stock applications to those producing 400 hp. New units were available through Pontiac parts departments until a few years ago. Used units are at least 30 years old, however, and the rubber isolator can deteriorate and/or shrink, allowing the outer ring to rotate. That not only affects spark timing accuracy, it can affect the damper’s balance, negatively impacting its ability to dampen harmonics.
In my opinion, after a thorough visual inspection and physically verifying that its outer ring hasn’t slipped, a used 1968–1979 balancer is adequate for stock-type rebuilds or those with very mild performance modifications only. I strongly suggest one of the many aftermarket Pontiac dampers available today.
Powerbond offers three internallybalanced, stock-sized Pontiac dampers. That includes an OE replacement for engines producing up to 400 hp, a Street Performance unit for use up to 600 hp, and an SFI-certified Race Performance damper for applications beyond that. The OE replacement and Street Performance units use a cast hub and outer ring and sell for around $100. The Race Performance unit uses a forged hub and outer ring and sells for less than $200. Powerbond injects rubber onto the hub and ring assemblies during production to positively secure the components for maximum strength and dampening ability. While Powerbond dampers cannot be rebuilt, the reasonable cost makes replacement a cost-efficient solution.
BHJ produces quality harmonic dampers for many engines including the Pontiac V-8. Its damper features a billetsteel inertia weight that’s isolated by rubber from a crankshaft hub constructed of billet steel or aluminum. The steel hub is available with a stock-type slip fit, or a press fit for high-performance applications. BHJ’s damper is SFI certified, measures 6.8 inches, and is internally balanced. While designed to accommodate other factory accessory pulleys, it is not compatible with the original A/C units. The BHJ balancer sells for about $450 and is ideal for engines producing as much as 1,200 hp, or even more.
ATI’s SFI-certified Super Damper is a multi-piece design with a crankshaft hub constructed of high-quality steel. The internal inertia weight is isolated by rubber and encased by inner and outer shells available in steel or aluminum, and in two different diameters. ATI recommends its 6.325-inch damper for engines producing as much as 600 hp and its 7-inch unit for applications beyond that. The Super Damper, which sells for about $400, is internally balanced and fully rebuildable. It does not always accept stock pulleys, however. In my opinion, the Super Damper is among the very best for max-performance applications.
Engine bearings are used to support components within the engine that are in constant motion, such as the crankshaft and camshaft. A hydrodynamic oil wedge prevents the component journals from actually contacting the bearings during normal operation. A bearing must be durable enough to prevent distortion or deformation under myriad loads for extended periods, yet soft enough that it allows dirt and foreign material to imbed into it as opposed to damaging the journals. It must also resist corrosion and heat.
Considered wear components, bearings are designed to survive an engine’s lifetime, assuming it’s operated within its intended parameters and regularly maintained. That duration may be 100,000 miles or more for passenger car service or as much as several dozen passes in a highend race engine. At the time of rebuild or refresh, a normal running engine with properly selected bearings leaves the component journals in the best possible condition, requiring the least amount of preparation for use with new bearings.
Modern bearings feature a multilayered construction that consists of an aluminum or steel shell (or backing) for support, an intermediate layer for strength, and a soft, outer overlay. That overlay is generally comprised of a soft metal, such as a lead alloy, which offers a high level of “imbedability” to absorb dirt and particles without damaging the crankshaft journals. Babbitt is another very soft, lead-like material that’s also commonly used. Neither is capable of enduring high loads for long periods without flaking apart if layered too thick, however.
Combining a thin overlay of lead or Babbitt with an intermediate layer of copper, lead, and/or nickel allows the bearing to perform its intended function for extended periods. Such trilayer or multi-layer bearings are commonplace in today’s industry. While Babbitt is still used in some instances, an overlay of lead, tin, aluminum, or some combination of them is often used in specialty bearing sets where heavier loads are common.
Crankshaft bearings are a two-piece design where the upper half resides in the block or connecting rod, and the lower half resides in the corresponding cap. ACL, Federal-Mogul, King, and Mahle/Clevite (Clevite) are among the best crankshaft OE replacement-bearing suppliers for Pontiacs today. Depending upon the manufacturer, bearings are available in standard dimensions, .001- inch undersize and then in .010-inch increments. Present undersize is up to .030 inch for main journals and .040 inch for Pontiac- and Chevy-size rod journals. You may need to check with the manufacturer for current availability.
Clevite and Federal-Mogul bearings seem to be the most popular with Pontiac engine building professionals. In addition to OE lines, either company also offers a “performance” bearing line designed for higher loads. Performance bearings are generally harder, and while better at enduring heat and heavy loads, they can resist some materials that can otherwise damage or score the crankshaft journal surfaces. Performance bearings can also be tougher on the journals of a cast crank. An artificial surface hardening process is a worthwhile consideration when using specific bearings in certain applications.
Main Bearing Grooves
All Pontiac main bearings are grooved to provide a path for pressurized oil to access the rod journal lubrication passage. While it might seem that using a main bearing set with upper and lower halves that are fully grooved would provide maximum rod lubrication, the grooving reduces bearing surface area, and that can compromise its load-carrying capability. While some main bearing sets are available with full grooves in each bearing half, and they may be completely adequate for a stock-type rebuild, I don’t consider them the best choice for very high performance use. Failure can occur at the highest loaded area, which is found at the lowest point in the main cap.
A crankshaft with cross-drilled main journals, such as the Pontiac 455, can maintain constant rod journal oiling while supporting the greatest load by using a main bearing set where the upper half is fully grooved and the lower half is solid. Most factory 3-inch crankshaft castings aren’t cross-drilled, however. For many years, cross-drilling the main journal and using a half-grooved main bearing set was the only way to attain maximum rod journal lubrication and load-carrying capability in such combinations. That’s no longer the norm.
Within the past several years manufacturers have developed main bearing sets with a fully-grooved upper half and partially-grooved lower half. In addition to constantly supplying oil to the connecting rods, the partially-grooved bearing provides full bearing width at the highest loaded area and places pressurized oil very close to it. Grooved across about 220 degrees of the journal surface, these “3/4 grooved” main bearings are the choice of most Pontiac engine builders for their excellent lubrication and surface strength qualities. Engines with forced induction or nitrous oxide may require different bearings, so be sure to discuss it with your Pontiac engine building specialist.
The excellent film strength of modern oil and state-of-the-art machining processes allow for adequate lubrication with bearing clearances that are slightly tighter than what you might find in older engines. Modern passenger car engines often specify 5W-20 or 5W-30 oil, which flows better through tighter clearances than heavier oil, while reducing horsepower loss and improving fuel economy. Lightweight oil isn’t the best choice for all applications, however, particularly if the engine wasn’t designed for use with it.
High-performance engines can generally tolerate slightly greater than normal clearance for many reasons. It increases oil to flow across the bearing surface at all times and allows the use of heavier oil such as 15W-40 and 20W-50, which doesn’t thin out as much as lighter oil as it heats up. Circulating heavier oil consumes a few horsepower, but it can better protect bearing surfaces in myriad speeds and conditions. Some racers prefer lightweight oil to free up a few horsepower, but I feel it’s best in instances where an engine is regularly torn down and the bearings can be inspected for lubricationrelated wear, and adjustments made.
Generally, a high-performance engine requires about .001 to .0015 inch of bearing clearance for each inch of journal diameter. Pontiac originally specified about .002 inch of rod journal clearance and .0025 inch of main journal clearance for its V-8s. I consider that an excellent starting point for most high-performance rebuilds, but your engine can likely tolerate closer to .003 inch or slightly more without issue. It’s difficult to suggest a specific amount of bearing clearance that applies to every application, however, because it can vary with such factors as operating range, expected load, cylinder pressure, oil pressure, and oil viscosity.
It should also be noted that not all bearings are created equal. Some are tighter than others. Federal-Mogul bearings generally run about .0005 inch more clearance than others. For example, if you find your clearance a bit tight with Clevite, a set of Federal-Mogul bearings might provide you with the amount of the clearance you need. Other bearings, such as those from Clevite with an “X” in the part number, are designed to provide .001-inch greater clearance than a standard bearing. Clevite’s H-series bearings that contain an “N” in the part number are narrowed slightly to provide greater crankshaft fillet clearance when using aftermarket units. Federal-Mogul’s performance bearing shares a similar characteristic.
Written by Rocky Rotella and Posted with Permission of CarTechBooks