The Ford FE engine family shares common key crankshaft dimensions, making it fairly easy to interchange from one displacement to another and allowing a broad selection of strokes and materials (OEM and aftermarket).
In the original-equipment world, a wide range of crankshaft strokes was available over the 20-year span of FE production (1958–1978), from the short-lived 3.300-inch-stroke 332-ci engine through the 3.980-inch-stroke 428. Any of these can be physically installed into any FE block providing that coordinating rods and pistons are used.
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Original-equipment crankshafts were made from either cast-nodular iron or forged steel. The nodular-iron cranks have proven to be extremely durable and are found in the vast majority of production engines. A steel crankshaft is inherently superior— especially in severe service, in which it is exposed to extremes in terms of power or cycle fatigue. A road-race engine is exposed to extreme cycle fatigue because it is subjected to long periods of heavy throttle and transitional loading. A steel crank is ideally suited for this application. On the other hand, a cast-nodulariron crank is better for the budgetconstrained street-oriented builds and many drag-race applications because these cranks are typically subjected to full-throttle operation for shorter periods of time.
Steel crankshafts were installed in the always-rare 427 performance engines with their 3.780-inch stroke and in medium-duty truck 361 and 391 engines. The limited supply of factory 427 steel cranks in repairable condition drove their cost beyond the reach of many engine builders several years ago. There are a scant few NASCAR 427 steel cranks that use a wider connecting rod and bearing than common OEM equipment. Wi th these supporting parts being nearly unobtainable, the NASCAR cranks are best left in the hands of collectors who have a demonstrated need for such parts.
It has become quite common to modify the 3.780-inch-stroke steel 391 truck crankshaft, converting it into a performance piece. The truck crankshaft has a larger-diameter snout where the damper mounts, as well as a different flywheel mounting flange and a counterweight combination designed for external balance. The pilot-bushing (or converter snout) hole in a steel truck crankshaft is larger in diameter as well, mandating a custom pilot or converter bushing for use in passengercar applications. The bushing must have the same ID, but the OD is larger. The required modifications are time consuming, but a skilled crankshaft shop can handle them. The crankshaft nose needs to be cut down to the standard 1.375-inch FE diameter, the flywheel mounting surface is shortened by about .060 inch, and the counterweights need to be cut down before balancing is possible. The supply of usable 391 cores has also dwindled in recent years, increasing the cost of the finished product, but this remains a viable option for those needing a steel crank within the stock stroke ranges at half the cost of a custom billet.
By far the most common factory offerings were the 3.500-inch-stroke cast crankshafts found in 352 and 360 engines and the 3.780-inchstroke cast units common to 390s. The highly sought-after 3.980-inchstroke cranks were only used in 428 applications and for two years (1966–1967) in Mercury 410 engines. A few of the 428 crankshafts have additional center counterweights, and were specified for vehicles equipped with the Super Cobra Jet (the “Drag Pack” option). Your odds of finding one of them in a normal swap meet or junkyard are slim.
Once you’ve seen an FE crankshaft, it’s pretty easy to pick out another one among any collection of parts. They have a unique long front snout similar to that of the 429/460 parts, but are much smaller in main journal and counterweight size.
It’s a fair bet that the average FE crankshaft you find in a parts pile or swap booth will be a cast 390 or 360 piece. If you are really lucky, you may find a 428 crank. A steel truck crankshaft occasionally shows up, but most often they have been turned .030 or .040 under. A serviceable steel 427 crank is extremely difficult to find outside of Ford specialty retailers or among dedicated racers.
It’s fairly easy to tell a cast crankshaft from a steel one. The cast crank has a very thin parting line where the two halves of the mold meet one another. In comparison, the steel crankshaft has a thicker parting line—usually between 1/4 and ½ inch wide.
Ford forges or casts numbers on the counterweights of the FE cranks which may simplify identification. As is the case in most FE parts, the numbers are helpful but not definitive. Often they are useful for exclusion; if a crank is stamped “2U” it’s obviously not a 428 part, but the absence of any stamping number does not preclude it from being one.
Here are some common casting marks; it’s by no means a comprehensive list:
- The cast 360 often has a 2T or 2TA
- The cast 390 often has a 2U or 2UA
- The cast 428 has a 1U, 1UA, or 1UB
- The cast 428 SCJ has a 1UA or 1UB
- The steel 427 may have a somewhat appropriate “$” sign
These parts are now 30 to 40 years old and have often seen a vast amount of modification, alteration, repair, and service. By far the best way to identify the crank is to measure the actual stroke using V-blocks or even an engine block with a couple main bearings set in it. The stroke variances are large enough so that you don’t have to be perfectly accurate for basic ID; even a ruler does the job. It is around 3.5 inches for the 360, just over 3.75 inches on the 390 cranks, and nearly 4 inches for the 428 version. The extra center counterweights on a 428 SCJ crank are obvious, as is the large 1.750- inch-diameter snout of an unaltered steel truck crank.
The past few years have seen an explosion of aftermarket products for the previously neglected FE engine family. Currently, many crankshaft options are readily available. In most cases, these cranks are imported products with a broad range of quality. However, they are also the foundation for economical assembly of some powerful but previously uncommon combinations.
Scat was first to the aftermarket with low-cost stroker crankshafts for the FE. And among the imported products, it seems to stand out in terms of having very consistent dimensional quality. At this time, it offers nodular iron cast cranks in strokes of 3.980 inches (essentially a 428 replacement item), 4.125 inches, and 4.250 inches.
The Scat 3.980-stroke crank is designed for internal balancing, which differs from the factory piece. However, other critical dimensions, such as main and rod journal diameters, are the same as the original Ford parts. This crank is a good choice for upgrading or service while using existing OE dimension rods, but the flexplate or flywheel needs to be a 390 part; original 428 parts have balance weights on them and will not work correctly.
The 4.125- and 4.250-inch-stroke crankshafts use 2.200-inch-diameter rod journals. They are designed to be run with common big-block Chevrolet bearings and connecting rods— most often in lengths of 6.700 or 6.800 inches.
In four years of testing and abuse, I have yet to break one of these cast 4.250-inch cranks—at power levels exceeding 750 hp. Intuitively, this has to be approaching the design limits of the material, though, and an alternate should be considered at that power level.
Also available are imported forged crankshafts from other manufacturers— currently in strokes of 4.125, 4.250, and 4.375 inches. These should, by virtue of the claimed 4340 forged-steel alloy, be a physically stronger option for higher-powered or road-race applications. These do not have the same level of machining quality, though, and should be thoroughly inspected and corrected prior to installation.
The top of the FE crankshaft food chain is a billet piece. Available from a number of suppliers including Scat, Crower, and Moldex, a billet crank is cut from a huge piece of bar stock, and can take on almost any stroke and design. These are normally made to extremely highquality standards, and come with a matching price tag.
Dimensional and Physical Inspection
The most important descriptors for any crankshaft (OEM or aftermarket) are “solid,” “straight,” and “round.” These terms apply to the crank as a whole as well as to each individual journal.
Checking the crank for straightness can be done either on a set of V-blocks or, lacking those, you can use the block itself by cradling the crank with bearing shells in the front and rear journals only. Use a dial micrometer on the center journal to see whether it’s straight or not. Try moving a bearing fromone end to the center and rechecking at the end journal. While the factory-accepted tolerance per the book may be higher, anything beyond a few “tenths” is a potential problem if clearances under .0030 inch are expected.
The same holds true for main and rod journals. These need to be checked in multiple places around each journal, and on at least a few spots front to rear. It is common to find a rod (or main) journal that has significant diameter differences forming either a tapered or barreled shape. Once again, any variance beyond a few ten thousandths of an inch can lead to early bearing wear or failure. Out-of-tolerance journals are common in used factory parts as well as brand-new items. You need to check. Your crankshaft machinist can grind to the next undersize if needed to straighten out a lot of these variances— a pretty common occurrence on even new imported crankshafts.
There are additional dimensional specifications for rod journal width and main thrust journal width. Rod journal width, along with the dimensions of the chosen connecting rods, determines the rod side clearance. This is a more forgiving clearance with a broad acceptable range (.008 to .020 inch is common), but still something that needs to be validated during assembly. Thrust journal width can be compared to specs while actual thrust clearance, a critical dimension, cannot be determined until the crank is installed in the block with the chosen bearing.
Cranks should be checked for cracks using Magnaflux equipment. While a good idea for any part, this is particularly important when reusing a cast crank because it is very common to find fatigue cracks around the rod journal radii alongside the counterweights. Sometimes these are surface flaws that can be removed by grinding down to the next undersize—sometimes not.
Throw index and stroke variance are less often checked in the typical home engine build, but the latter, in particular, is very important to determine. If you’re not paying attention, it can “catch you,” and the consequences are catastrophic. A lot of folks target a near-zero deck clearance on their engine project—simply adding the nominal dimension of connecting rods, pistons, and crank stroke—and then machine the block decks to the combined value. Differences in stroke measured from journal to journal of .001 inch or more are not unusual, and I’ve seen more than .005 inch on some import crankshafts. A bit too much will impact compression ratio, piston-to-valve clearance, and pistonto- deck clearance.
Before you pronounce your crankshaft candidate a “winner,” you still need to take a quick look at the snout diameter, the condition of the keyway slot, and the threads for the damper bolt. While often repairable, damage in these areas often renders a crank financially unsound as a prospect.
Connecting rods are perhaps the most critical short-block component in terms of load and the impact of a failed part. Rods do not really fail from horsepower. Compressive loads are rarely a problem for a decent modern connecting rod, and all FE connecting rods (both original and aftermarket) are forged steel. Commonly, the rods fail from either cyclic fatigue or overload stress. However, rods must not be the weakest link in the rotating assembly, so you need to select rods that are compatible with the engine combination.
The stress loads come from the weight of the piston and the amount of RPM the rod is subjected to. Higher RPM and/or heavier pistons take their toll on any rod. Cyclic fatigue results from the additive impact of many such loads over time. Every time the rod is put into an elastic state from load it reacts metallurgically, and these minute changes in metallurgy accumulate over time and lead to fatigue. This is the reason that a roadrace application requires a better quality rod than a similar horsepower drag car; it’s the number of cycles under high RPM.
With the single exception of the slightly longer and not particularly desirable 352 parts, all FE-family connecting rods share a common, nominal center-to-center length of 6.488 inches usually just specified as 6.490 inches. They also all have a median big end housing bore of 2.5911 inches and are designed to work with a .975- inch pin diameter. All FE Ford piston pins are of the floating design, and a bronze bushing in the small end of the rod supports the pin.
The standard service and high performance factory FE connecting rods can be divided into three general groupings. Over the 20-year span of production, there were a number of forging numbers used and some of these were used with no apparent rhyme or reason. So, as with many other numbers on FE parts, the forging number is useful but not truly definitive for identification.
The most common passenger car and truck rods used a 3/8-inch rod bolt and nut for big-end attachment. These are suitable for stock rebuilds and mild-performance applications when upgraded with ARP replacement fasteners and proper reconditioning.
The heavy-duty rods as found in the 428 Cobra Jet engines are less common. These use essentially the same forging blanks, but have a larger-diameter 13/32-inch rod bolt and nut. It is worth noting that the ARP replacement fastener for these rods has the larger shank diameter but still only a 3/8-inch threaded section These are likely to be stronger in service if (a big “if”) you assume that the rod bolt shank diameter is the weak point in the package.
High-performance 427 engines, as well as the 428 Super Cobra Jet, received the “LeMans” rods. There were a few variations on these, but they all shared a much larger and beefier design along with capscrews and locating dowels instead of the more common nut and bolt fasteners. Despite an undeserved reputation for early bolt failure, these are actually very robust parts and are the obvious design forefathers for many of the current aftermarket rod offerings. Replacement bolts are readily available, but the dowel sleeves are problematic at the time of this writing. The NASCAR version of the capscrew rod is wider and heavier, and requires a matching and equally rare crankshaft.
The biggest problem with any of the factory rods is a simple one of age. With 30 or more years of undocumented service, of unknown severity, many of these are simply getting worn out. Even a thorough physical inspection and good reconditioning techniques do not uncover metal fatigue. Fatigued rods often fail in the same area, breaking about 2 inches below the pin. The cross section of the factory FE rod is surprisingly thin in that area, and it flexes (and breaks) like a repeatedly bent coat hanger after an unknowable number of cycles and loads. It usually happens to the guy who claims, “I’ve gone xxx number of years with stock rods…you don’t need anything else.” He is correct in a certain sense. The factory rod could withstand a real beating in 1968 and 1978, and in 1988, when it had better integrity, but it might break instead of bending in 2009. You just don’t know when.
There is a wide variety of aftermarket connecting rods available for the FE engine now. The general breakdown revolves around price point and design. Prices range from less than $300 to more than $1,500 for steel rods that have similar descriptions but very different quality. The designs are either “I” beam or “H” beam with arguments for and against each at every level of the sport.
The replacements for factorydimension rods are comparatively limited, while the rods used in common stroker kits are based on popular 6.700- or 6.800-, 2.200-inch journal big-block Chevrolet parts and thus have every imaginable option and source.
With notably rare exception, all aftermarket rods come with some sort of ARP fastener. Excellent products combined with excellent marketing have virtually made this a “must-have” feature for rod sales.
The lowest-cost connecting rods are all imported parts sold in unmarked white boxes under a plethora of house brands. The cheapest of these should best be viewed as a replacement for stock rods and little more. With questionable metallurgy and poor dimensional integrity, a really cheap connecting rod is not a good place to save a couple dollars. Reconditioned stock rods are often a safer bet in a stock rebuild because, in many cases, they’re dimensionally superior. Scat and Eagle rods are found on the next tier up. At a price point around $500 per set, these are still imported but have considerably higher standards for quality and machining. In this range the H-beam design seems markedly superior, not due to any particular engineering advantage, but because of a nicer fit and finish.
With the addition of the optional ARP 2000 bolts, I’ve run the Scat H-beam parts at power levels beyond 750 hp and 7,000 rpm without incident, and feel confident in recommending them for most high performance street cars as well as moderate drag-race applications.
At the upper end of the FE rod spectrum are true premium rod sets, which cost in excess of $1,300 and sometimes much more. These are designed for the most serious dragrace engines, as well as road-race engines that produce up to 800 hp. Manufacturers, such as Oliver, Crower, and Carillo, make outstanding quality parts using superior metals and far better dimensional accuracy. While unquestionably superior to the lower-cost parts, the engine builder needs to make the determination of whether the cost penalty outweighs the advantages. In a road-race Cobra or an 800-plushp drag car the choice is pretty clear, but less so in a street-oriented car or truck.
Several years ago the aluminum rod was the status quo for a serious drag-race application. The noted advantages of an aluminum rod are reduced weight and a degree of compressive “give” under severe load, which keeps the shock from being transferred to the bearing. The downsides are a greater physical size, dimensional variances under temperature and load conditions, and a shorter cycle life. While still popular in some circles, they are not nearly as dominant as they once were, with the trend for many sportsman drag-race engines going to the more durable steel rod options.
Currently, I am not aware of any FE-specific aluminum rods on the market. There are several billet rod manufacturers who will gladly make some for you if you feel the need. The rods used in most stroker applications are based on the big-block Chevy and are readily available.
With most FE engines destined for sportsman drag racing, Cobra road racing, and street performance, the number of builds that take advantage of an aluminum rod’s characteristics are relatively few.
Checking the Rods
Any connecting rod chosen, whether original or aftermarket, should be subject to a thorough inspection before being put into service. Similar to a crankshaft, the rods need to be solid, round, and straight.
Rods should be X-rayed or Magnaflux inspected for cracks or flaws. This is particularly important when reconditioning rods that have already been run for a period of time. Any rod that shows a flaw should be discarded; no common repair is possible.
The rod’s big-end bore should be round, straight from one edge to the other, and within diametrical specifications. The diameter is critical because it directly impacts the bearing crush. “Crush,” by definition, is a press fit and is the only thing that keeps the bearings from spinning in the rod bore. The little locating tabs do not provide antirotation; the crush fit prevents bearing rotation. Newer engines do not even use locating tabs. Equally important is that the bore diameter “repeats” when loosened and retorqued. Bolt holes that are off from perpendicular, misaligned spot faces, or angled cap surfaces cause the rod cap to shift and change dimensions when assembled. Such issues are common to the lowest-cost rods and expensive to repair, often negating any savings.
The rod’s small-end bronze bushing must be straight, round, and sized to the piston pin. With a clearance specification among the tightest in the engine (+/- .001 inch), there is little room for error. The fact that piston manufacturers, including OEMs, do not agree on the exact pin diameter dimension makes this more critical. When checking pin fit, be sure that any shipping lubricant has been thoroughly removed. Some imported rods have a lot of protective anti corrosive goo on them, and it can really mess up your measurements.
Obviously, a connecting rod needs to be straight in all planes and the pin bore needs to be aligned with the bigend bore. If they’re not straight and in line, toss the rod.
That pebbled surface on stock rods is from shot peening, which adds surface hardness and resists stressriser formation. If you choose to polish the beams on some stock rods, you should have them re-shot peened to restore that surface. Of course, this adds cost, further justifying the purchase of aftermarket rods.
Engine bearings are a critical element in any engine, and the FE is no different. The main bearings are fed oil from the galleys in the block. The oil is transferred through grooves in each bearing that in turn directs that oil to the rod bearings through passages in the crankshaft.
These grooves in the bearing can be only in the upper shell, or go all the way around the inside diameter (full groove). Our preference is for the most current design from Federal- Mogul, which uses a groove configuration going 3/4 of the way around the inside diameter. The 3/4 groove bearing allows more surface area to remain on the highly loaded lower portion of the bearing, while still providing more oil to the rod bearings than does a 1/2 groove design.
Some of the inexpensive rebuilder quality main bearings use the same shell top and bottom putting a big oil hole right at the point of the highest load. Avoid these.
The thrust bearing in an FE is on the number-3 main. Folding a bearing into the proper shape during the manufacturing process forms the thrust bearings. If the bearing is folded too far, or not far enough, it will not have proper thrust contact. This is the reason for working the crankshaft back and forth a few times during assembly; it helps to form the bearing and correct variances in thrust-face angles.
Rod bearings in performance applications have either a wide chamfer on one edge or a narroweddesign. This provides necessary clearance for the larger .125-inch radius found on high performance crankshaft journals. Without the proper clearance, you may find that the rods bind up when assembled and the bearings wear prematurely from edge loading and contact.
Race bearings are made from higher-quality materials than passenger- car bearings. The difference in cost is modest, and I always specify a race bearing in any build. Contrary to some beliefs, a race bearing is not harder on crankshafts. The only downside to running a race bearing on the street is that it is less tolerant of debris. Frequent oil changes are the norm for a performance build, though, so this is really a non-issue.
A brand-name race bearing has a stronger steel backing, allowing a higher degree of crush to resist spinning and improve heat transfer. Race bearings also have greater eccentricity, which prevents crankshaft contact in cases of rod or main cap distortion.
Do not use abrasives on a bearing if at all avoidable. They get pushed into the lining material and wear on the crankshaft. If you must clean or burnish the bearing, you can try some WD-40 on a piece of brown paper from a shopping bag. It cleans the surface without abrasives.
ARP recommends repeated tightening and loosening cycles for rod bolts before putting them into service. This serves to burnish the threads and provides smoother thread engagement and pull up to torque. You will get an adequate number of cycles when assembling and disassembling rods for cleaning and checking clearances. Be careful selecting products used to clean the fastener threads between tightening cycles; chlorinated solvents, such as brake cleaner, are corrosive to certain bolt alloys.
Most rod and fastener manufacturers prefer to use bolt stretch, rather than torque readings to determine adequate fastener tightness. While functionally superior, it can be difficult in some engines to measure stretch with the rod in the block. I often stretch the bolt to spec on the workbench and record the torque value needed to reach that point using that torque spec for final assembly.
When installing rods into the engine, remember that the rod’s bigend bore has a large chamfer on one side and a small chamfer on the opposite side. The larger chamfer always faces the crank counterweight and the small chamfers face each other. Mixing this up usually puts the bearing into contact with the crank journal radius causing rapid wear, if you are even able to turn the engine over at all.
Written by Barry Robotnik and Republished with Permission of CarTech Inc
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