Where Is the Keyway Mark on the Crank of Chevy 3500 Diesel

Crank Identification

All small-block Chevrolet crankshafts are made from two basic materials. Prior to 1963 all cranks were made from forged steel alloys, but nodular iron has long since become the standard crankshaft material. Forged cranks are generally preferred for performance work, but for most street engines the use of a forged crank is purely a luxury. Nodular iron is a very stable material that provides good service in any street or bracketracing engine. It has the ability to flex under load and withstand considerably more punishment than you might expect.

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It's not difficult to tell a forged crank from a cast crank if you know what to look for. A cast crank will have a thin parting line down the front of the first throw, while a forged crank will have a wide forging mark (finger).

Large-journal steel cranks in the 350- and 327-ci configuration are not always easy to find, but if you happen to spot some, there's an easy way to tell them apart. The rare 327-ci crank has a large dip or notch (arrow) in the front arm. The steel 350 crank has no notch.

All production cranks from 1955 to 1985 have a 3.58-inch diameter flywheel bolt pattern on the flange. In 1986 however, the flange bolt pattern diameter was reduced to 3.00 inches to facilitate the use of a one-piece rear seal (left). This pattern is easily seen in the accompanying flexplate photos. The flywheel bolt pattern on the late-model flexplate (left) is clearly smaller in diameter and tighter than that on the early model unit (right) with a larger bolt pattern.

Since 1986, all production small-blocks have used a one-piece rear main seal that mounts in an aluminum adapter bolted to the rear of the block as shown here. Late crankshafts were redesigned for the one-piece seal and incorporate a large round flange. Late-model cranks are not compatible with early blocks. However, GM crankshaft seal adapter P/N 10051118 permits the installation of early-style two-piece rear seal cranks into blocks machined for the late-style one-piece rear seal.

Mic the crank journals to make sure they will finish grind to no smaller than 0.030-inch undersize. If the journals are already 0.030-inch undersize or greater, you may not find bearings suitable for performance work. Most bearings for 0.040 or 0.060-inch undersize journals are not designed for performance work and should be avoided. Find another crank.

If you will be using a manual transmission, make sure the crank has been drilled to accept a pilot bushing.

In 1967, the factory beganmaking available forged cranks with a special surface-hardening treatment called Tufftriding. Tufftriding is a chemical hardening process that imparts a very tough surface to the bearing journals. It does offer a significant decrease in friction, but again, it isn't really necessary in a performance street engine. The best advice we can give you is not to search for a Tufftrided, forged crank unless you are putting together a very serious engine.

Crankshaft science has progressed significantly, and you really can't go wrong with a well-prepped factory crank or on any of the top aftermarket brands. Stock cranks were available in stroke lengths of 3.00, 3.25, 3.48, 3.80, 3.75, and 3.10 inches, the latter two being offered only in nodular iron. These cranks are not all interchangeable. Some of the cranks have main-bearing journals and/or rodbearing journals of unique size to accommodate special engineering requirements. Currently, there are three different main-bearing diameters and two different rod-bearing diameters. The vast majority of available cranks have the current "standard" main and rod journals, but the small-block builder must be aware of the many combinations to ensure his combination is correct.

The 3.00- and 3.25-inch cranks are the only ones available with small main-bearing journals, although some later versions were also made with largemain and rod journals. The 3.10-, 3.80-, and 3.48-inch cranks are only available with the now-standard large main-journal size. The 3.75-inch crank uses a totally unique, even larger, main-journal size. The small mainjournal 3.00- and 3.25-inch cranks also had small-diameter rod journals,while all the rest, including the 3.75-inch crank, have the now-standard large rod journals.

As a point of reference, a smalljournal crank has 2.30-inch mains and 2.00-inch rods, a large-journal crank features 2.45-inch mains and 2.10- inch rods, and the 3.75-inch crank (400 ci) has 2.65-inch mains and 2.10- inch rods. There are also early 3.00- inch stroke cranks available with large journals (1968–1969 302-ci Z28), and 3.25-inch cranks with large journals (1968–1969 327-ci and 1968–1973 307-ci).

Small-journal, 3.00-inch stroke cranks all have round counterweights, relative to the crank centerline. The Tufftrided, 3.00-inch, large-journal 302 cranks have the fan-shaped counterweights, similar to late 327- and 350-ci cranks. Cranks manufactured prior to 1968 all had a round flywheel flange, while those made in 1968 and later had irregularly shaped, counterweighted flywheel flanges.

There are some cast 3.00-inch cranks around, and they are usually found in 1966 and 1967 283-ci engines and a few late 1965 283-ci engines. Forged 3.00-inch cranks were still made during this period, but most of them were used in truck motors. The cast 283 cranks should only be used in 1962 and later engine blocks, because the front counterweights interfere with the front main bearing webs.

Rod length is consistent in all engines except the 400 (3.75-inch stroke). Therefore, stroke changes must be accompanied by piston compression- height changes. Piston compression height must always be matched to the stroke of the crankshaft, except in the unique 400, where a shorter connecting rod compensates for the increase in stroke. All 400-ci pistons have the same compression height as 350-ci pistons, which allow the 350 internals to be installed in a 400 block rather easily. The late model 383 crank is a 4340 steel crank with a 3.80-inch stroke. It has a one-piece rear seal.

Having covered the basics of smallblock crankshaft identification, we can now look at some of the less noticeable differences that set them apart. To begin with, there is absolutely no difficulty in identifying a forged crank from a cast crank. You don't have to worry about casting numbers or plinking cranks with a hammer. On all cast cranks, the flashing marks are readily distinguished as a thin seam along the edges of the counterweights. It is most noticeable on the front arm of the crank. Forged cranks have a wide flat rib on the front arm. The flashing along the edges of the counterweights is ground off, so they also have a very smooth, even surface compared to the rough, grainy surface of a cast crank.

You can also look for specific clues and use the process of elimination. Remember that there are no largejournal, 3.00-inch stroke cast cranks; no 3.25-inch stroke, small-journal cast cranks; and no small-journal 3.48- inch cranks, forged or otherwise. All 3.75-inch cranks are cast, as are the 3.10-inch cranks. All 3.80-inch cranks are forged. If you have a 3.00-inch crank without notches in the full round flywheel flange, it is one of the original 283 forgings. A round flywheel flange with two balancing notches indicates an early 327 crank (3.25-inch), which is further distinguished by a wide front arm and flattened counterweights to clear the pistons. A 3.00-inch, 302 crank will have a round flange with a single balancing notch, and a narrow front pin arm. The counterweights are also round and not flattened, since piston clearance is not required with the 3.00-inch stroke.

Inspection and Prep

Once you have located several choices that will serve your purpose, a careful inspection is in order to determine the best of the bunch. The final criterion for crankshaft suitability is an absence of cracks. This should only be determined by a thorough Magnaflux inspection. Most cracks occur in the radius where the rod journal joins the throw, and they are sometimes difficult to pinpoint. If the crank is intended for street use and the crack is small, it can sometimes be removed when the crank is reground. This is a determination you will have to make in collaboration with your crank grinder.

Magnafluxing is another essential step in crank inspection. This procedure locates tiny fatigue cracks and is cheap insurance against premature engine failure.

Prior to final assembly, the crankshaft should receive a thorough cleaning, including a vigorous attack of all the oil holes with a small cleaning brush.

Oil supply holes on the rod and main journals should be lightly chamfered to promote good oil distribution to the bearings. Don't get crazy, just open up the edges approximately 0.030 to 0.060 inch.

Straightening a crankshaft is a simple process. Pressure is applied to the crank to bend it in the right direction. Fix it in place with a hammer blow. This procedure does not shorten crankshaft life, but it has become relatively unnecessary with the broad availability of inexpensive aftermarket cranks.

In any instance, there are several checks you can make prior to Magnafluxing to determine the suitability for your particular application. The bearing journals should all be carefully mic'ed to ascertain their present size. Each journal should be examined for evidence of excessive wear or discolored surfaces, which would indicate metal-to-metal contact. If any of the journals are badly nicked or peppered, move on to another crank. Check each journal radius fillet for obvious signs of damage. The nose and keyway section should be relatively free of damage, although minor damage is usually repairable. Inspect the thrust surfaces of the rear main journal for damage or excess wear and determine if the crank will accept a pilot bushing. Some early cranks produced for use with Powerglide- equipped cars were not drilled for pilot bushings. If the crank survives these preliminary checks and you find it free of cracks, it will usually provide excellent service with only minimal preparation.

Prior to finish-grinding the crank, there are a number of steps you can take to ensure its integrity. Regardless of the intended use, have it hot tanked to remove grit and grime. Then attack the oil holes with a small wire brush. Rifle-bore kits have the right kind of brushes, but similar brushes are also available over-the-counter from reputable speed shops or machine-shop suppliers. Use a medium file or heavy grit paper to carefully deburr the counterweights and be sure to break the edges of any holes that are not on the journals. The oil holes on each journal should receive a very slight chamfer; nothing big, just chamfer the edges approximately 0.030- to .060- inch. Don't grind a giant trough around the hole. All you're doing is reducing the load-carrying surface and wasting your time.

For street use, it is perfectly acceptable to cut a crank undersize as long as the shop maintains an adequate radius on each journal. Undersized bearings provide excellent service in thousands of street and bracket racing engines. Problems are rare if the crankshaft grinder is reputable. Sure, top engine builders check every clearance fifteen times, but thousands more competent assemblers just install 'em and run 'em—and they live. If you're not building an all-out racing engine and you can trust your crank grinder, it will save a lot of time.

There are two things you never do to a small-block engine, regardless of its application. If your machinist suggests grooving the crank journals, find another machinist. The same goes for grooved bearings. Never use fully grooved bearings in a small-block engine. The correct bearings are only grooved on the upper half. The lower half carries an incredible load and there's no sense in reducing the amount of load-carrying surface. Cross drilling is an acceptable practice, but it's old technology. Keep in mind how manymillions of small-blocks provide heavy-duty service every day with perfectly stock oiling systems.

You should also check the stroke and straightness of your crank prior to balancing the internal engine assembly. Most cranks will not require straightening, but when you do run across a bent crank, it will usually be off by quite a bit. To determine the condition of your crank, mock it up in the block with the front and rear bearings installed and lightly lubed. Torque the main caps to the correct spec and then arrange a dial indicator so it can read off the center main bearing journal. Make certain the journal is free of oil and debris and then slowly rotate the crank while observing the dial indicator. The crank should be straightened if it has more than 0.003-inch of runout. This is a relatively simple procedure that can be handled by most competent crank grinding shops. You should make certain they don't try to straighten it in a hydraulic press. A knowledgeable crank man will use a large hammer to straighten a crank.

For street applications, you can install the crank just as you would for final assembly, with all the bearings in place and the main caps torqued (leave out the rear main seal for this check). Then try spinning the crank by hand. If you're able to easily spin the crank by hand, it will work just fine on the street.

Many racers prefer to have their cranks checked for perfect throw indexing, but in most cases this is an unnecessary step. The idea is to make certain that each crank throw is exactly 90 degrees from the next and that they are all in the proper relationship to the keyway on the crankshaft snout. More importantly, you should make sure the stroke lengths are equal. Sometimes a crank can be straight and properly indexed, but some of the throws will actually be slightly longer or shorter. This is an important determination to make before the crank is ground and balanced.

Balancing

In the great majority of engine rebuilds it is advisable to have the operating components rebalanced to ensure smooth operation and longevity. Critical balancing is helpful in a high-performance engine, but the greatest benefits are derived from achieving a smoother, longer-lasting engine. If you are rebuilding your street engine and you've changed pistons, you should get the machinist to weigh your old pistons and pins to determine the difference between them and your new ones. Even when the new piston is an exact duplicate, it should be checked. Sometimes a forged replacement piston will be slightly lighter than the cast piston it replaces because of the absence of the thermal expansion struts. In these cases, you may find that the manufacturer has tried to keep the weight constant by using a heavier wrist pin. This is a noticeable difference in some of the TRW 400-ci replacement pistons.

As illustrated in the previous pressure diagram, never use fully grooved bearings as shown on the right. Good high-performance bearings (left) will only be grooved on the top half, leaving the full width of the lower bearing to maintain oil film and minimize oil-film pressure.

It's common practice to use grooved bearing shells in the block but ungrooved bearings in the caps. This practice improves bearing life by reducing oil film pressure in the cap bearings. The original research was done by GM years ago and is illustrated in this diagram. Note that when the lower bearing is grooved, the oil film pressure is almost twice as high and much more likely to permit metal-to-metal contact.

Grooved main bearing shells are installed in the block. Main caps receive the ungrooved half to ensure long bearing life.

From a racing standpoint, balancing takes on a different character. Naturally, the lightest overall reciprocating weight (e.g., the weight of the rods, pistons, rings, etc.) is desirable, but this must be tempered by strength and reliability requirements. Balancing reciprocating weight is extremely important, because it minimizes rod, crank, and bearing stress. The rotating weight of the crankshaft transfers load across the main saddles to each end of the crankshaft, where the flywheel and the balancer help control crankshaft pulses. Many engine builders feel that overbalancing the entire assembly is an important step. Overbalancing is adding one to two percent extra bob weight during the balancing process. It is thought that this helps smooth out a high-RPM engine. Balancing is an important step, and you should always consider it for a high-performance engine.

Bearings

The type of bearings you use in your engine should complement the intended use. Since bearings are designed with various characteristics according to application, it's important to use the right ones. All engine bearings have different degrees of fatigue strength, corrosion resistance, and surface behavior built into them. You need to determine which of these criteria is most important to your application and select bearings on this basis. A high-performance street engine needs a high-strength bearing with corrosion resistance and surface behavior a secondary consideration. Speed Pro, TRW CL-77, and GM Moraine 400 bearings all share this characteristic. They do, however, require frequent oil changes since they have poor embedability, and the crankshaft can be easily scored by foreign particles.

Plastigauge is a common and surprisingly accurate method of checking bearing clearances when you don't have proper measuring equipment.

All small-blocks take crankshaft thrust on the number-five rear-main bearing. It receives direct pressure oiling and rarely causes problems. Thrust clearance should be maintained between 0.005 and 0.007 inch. Before checking the clearance, set the crank by driving it forward and backward with several raps from a brass hammer or a regular hammer cushioned by a small block of wood. Then set a dial indicator to read fore and aft movement at the front of the crank. To simulate crank thrust, pry it back and forth with a large screwdriver. Small-journal cranks require slightly more clearance than largejournal cranks because they tend to whip more. Clearances should be checked vertically in the bearing bore: 0.0025 to 0.003 inch for large journals, 0.003 to 0.0035 inch for small journals. If the thrust clearance on the rear main bearing is too small, increase it by installing the bearing halves in the rear main cap and sanding them against fine wet-dry paper on a surface plate.

Here are two 1053 forged-steel cranks from GM. Both are 3.48-inch stroke and have 2.100-inch large rod journals. The crank with the large round rear flange (left) can only be used in late-model blocks with a onepiece seal. The other crank with the squared-off rear flange (right) is designed for early blocks with a twopiece rear seal. However, it can be used in late blocks when they are equipped with PN 10051118 adapter, the PN 10121044 two-piece seal, the PN 12337823 retainer gasket, the PN 9441003 dowel pin, and a 1986 or later oil pan.

In a strictly drag race application, corrosion resistance and fatigue strength are less important because of the short duration of severe service. The most important considerations are embedability and conformability under stress. Moraine 400 bearings are a good choice here, but Speed Pro bearings are even better. With clean oil under adequate pressure, bearings should appear nearly new, even after severe or extended use. It's all in using the right bearing, the right oil, and proper clearance.

For street use, small-block bearing clearances should be kept absolutely stock. Chevrolet spent a bundle working out the ideal clearances, and who are we to argue with their obvious success? For high-performance and drag strip use, clearance adjustments are necessary. Many engine builders do not distinguish between large- and small-journal engines when setting clearances, but there are significant differences. The main difference is that small-journal cranks generally require slightly more clearance, because they tend to "whip" or flex more than a large-journal crank.

You'll never be far off if you set themupwithmain-bearing clearances between 0.003 and 0.0035 inch. Optimum rod-bearing clearances should be kept between 0.0022 and 0.003 inch. Large-journal cranks are more stable, so you can generally tighten up the clearances 0.0005 inch. Understand that these clearances are preferred, but you don't have to hit them right on the money. If you're within 0.0005 inch eitherway, you're in good shape. Just remember to give the small journals a tad more room to allow for increased flex.

It's highly unusual to experience bearing problems in a small-block Chevy. If you have trouble, retrace your steps and more often than not, you'll uncover the problem. Remember also that bearing life is contingent on well-prepared, round crank journals and round, well-aligned bearing bores. More often than not, clearances will be the last thing to cause problems. Whenever you're not sure about something, think stock, and 9 times out of 10 it will work just fine.

High-Performance Chevy Crankshafts

350 Forged Steel Crankshaft, PN 3941184 This 1053 steel crank has been nitrided to increase journal hardness; it carries forging ID number 1182. It is still a two-piece rear seal crank.

350 Cast-Iron Crankshaft, PN 14088527

This crank is used in the 300- and 330- hp 350-ci special performance service engines with identification code "SP." It requires a one-piece rear seal or a two-piece rear seal adapter.

350 Forged Steel Crankshaft, PN 14096036

A 1053 steel crank used in 1986 and later 350 engines. It has a 3.48-inch stroke and 2.10-inch rod journals and requires a one-piece rear seal. This crank is used in the ZZ3 engine assembly.

Crankshaft Forging, PN 10185100

This is the same raw forging used to make crankshaft PN 3941184, except it is forged from S38 micro alloy steel. It can be machined for a 3.46- to 3.50- inch stroke.

Crankshaft Forging, PN 24502460

This unmachined crankshaft gives engine builders the ability to customize their stroke to work in a particular class or build up. It has a large front section for machining to bigblock or small-block balancer size, and it will accommodate finished strokes from 3.20 to 4.00 inches. The 2.900- inch diameter main bearing journals can be ground to fit 400-ci small-block main bearings. This crank is forged from vacuum-degassed 4340 steel, which provides exceptional strength and durability. This is a "nontwist" forging, meaning all rod throws are forged in place. The large, circular counterweights are engineered to minimize bearing loads. The rod pin arms are lightened, and the machining pads found in production cranks are eliminated.

Crankshaft Seal Adapter, PN 10051118

This adapter permits the use of early style two-piece rear seal crankshafts in late model one-piece real seal type blocks. It's also used for installing a heavy-duty crankshaft in a Bow Tie block machined for a one-piece rear seal. It includes a two-piece aluminum seal retainer and related hardware, but does not include a gasket or two-piece seal.

Harmonic Balancers

All street and bracket racing engines should be operated with a good harmonic balancer. Without one, the crankshaft will surely crack. For a low-output, small-inch smallblock, the stock 283 balancer PN 3861970 works well. Never use it on a larger engine that will be revved to high RPM. The 302/327 high-performance balancer (PN 3817173) is a good choice for any engine. These large, eight-inch balancers are the best ones to use, and there are several of them. In 1969, there was a slight change in the position of the timing mark, so you should use one that matches your engine, unless you are planning to make up your own timing marker. Use damper PN 3947708 for the 1969–1975 engines. A special damper with a nodular-iron outer ring is offered for engines that will operate continuously at high RPM. It is offered as PN 364709, and Chevrolet recommends the outer inertia ring be pinned to the inner casting to prevent it from working forward or backward. All 400-ci engines are externally balanced with special balancers and flywheels. When building a 400-based engine, you have to use the special 400 balancer, PN 6272225. The 400 also uses a specially balanced flexplate, which is available as PN 340298.

Raw forging P/N 10051168 is the current factory choice for machining highperformance cranks with stroke lengths from 3.20 to 4.00 inch.

Most 1969 and later balancers have the timing mark 10 degrees advanced from the keyway centerline; the timing mark on earlier balancers was only 2 degrees advanced. To avoid any possible mismatches and timing errors, always check the accuracy of the timing indicator with a piston stop tool during preassembly fitting.

The harmonic balancer is a precision part of the engine and it should be carefully installed. Beating it on with a large hammer is not the answer. Commercially available installation tools screw into the front of the crank and let you pull the balancer gently onto the crank snout.

High-performance applications will want to use GM torsional damper PN 24502535. It's tuned for 9,000-rpm usage, comes fully degreed for your convenience, and is drilled and tapped for standard accessory drives. The damper is 7.74 inches in diameter and weighs 8.95 pounds. This same damper is available for a larger 1.598-inch blower crank snout under PN 24502535.

This heavyduty 11-inch diameter diaphragm clutch assembly PN 3884598 is a highperformance unit recommended for use with 14-inch flywheels PN 39911469 and 3986394.

Harmonic balancers should be pulled onto the crankshaft with the proper installation tool; never beat one onto the crank with a hammer. Most cranks made after 1967 had the nose drilled to accept a large balancer retention bolt. Early cranks do not have this feature, but it is a simple job for a competent shop to drill the crank snout. If you're serious about keeping your engine together, bolt the balancer on; it can and will come off if you rely on the press fit. Never use a balancer where the rubber mating surface between the hub and the outer ring is damaged. Treat the balancer as if it were another precision part of the engine—it is!

Note: Many of the part numbers listed here are out of production. They are provided as a reference for restoration efforts. Consult the GM Performance Parts catalog for current production damper availability.

6.75-inch Torsional Damper, PN 6272221

Used on most late 1969 and later production 305 and 350 small-blocks. Recommended for V-6 90-degree engines and V-8s with limited clearance. The timing mark is 10 degrees before the keyway centerline. Use with chrome timing pointer PN 12341904.

8-inch Torsional Damper, PN 3817173

Originally used on high-performance 302s and 327s produced from 1962 to 1968. The cast inertia ring is 111⁄16 inches wide, and the timingmark is 2 degrees before the keyway centerline. The damper ID number is 7173 and it has the pre-1969 timingmark, so don't use it with chrome timing pointer PN 12341904 unless you adjust the top deadcenter (TDC)mark.

8-inch Torsional Damper, PN 3947708

1969 302 Z28 damper. Features the 1969 and later timing mark location with a 15⁄16-inch-wide inertia ring and the timing mark located 2 degrees before the keyway centerline. Damper ID number is 7708, and it can be used with the chromed pointer.

8-inch Torsional Damper, PN 6272224

1970–1974 350, Z28 and L-82 damper. A cast-iron balancer with a 111⁄16-inchwide inertia ring and 1969 and later timing mark. Damper ID is 2224. Use with chrome timing pointer PN 12341904.

8-inch Torsional Damper, 400 smallblock, PN 6272225

Counterweighted balancer requires corresponding counterweighted flywheel for 400-cubic-inch engine or proper balance on 383 small-blocks. The timing mark is 10 degrees before keyway centerline, and it can be used with chrome timing pointer PN 12341904.

Heavy-Duty 8-inch Torsional Damper, PN 364709

Off-highway damper for competition use where production dampers are permitted. Features a nodular iron inertia ring and high temperature rubber for durability. The hub is balanced separately before the unit is balanced together. The heavy-duty damper carries ID number 4709 and the outer ring is marked "MALL" 0. The timing mark is 10 degrees before the keyway centerline, and it can be used with chrome timing pointer PN 12341904.

Torsional Damper—Standard Hub PN 24502534

Specially tuned dampers for use up to 9,000 rpm. They fit all small-blocks with standard size hub diameter; 70 durometer O-rings are used to dampen crankshaft vibrations. The black outer ring is fully degreed with contrasting white marks to simplify ignition timing and valve lash adjustments. The hub is drilled and tapped for standard pulleys and accessory drives. This damper is 7.74 inches in diameter and weighs 8.94 pounds (4.5 pounds inertia weight).

Torsional Damper—Large Hub PN 24502535

Same damper as PN 24502534 except for use with large-diameter 1.598-inch crankshaft nose, which is the same size as a big-block Chevy.

Written by John Baechtel and Posted with Permission of CarTechBooks

 

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Where Is the Keyway Mark on the Crank of Chevy 3500 Diesel

Source: https://www.chevydiy.com/1955-1996-chevy-small-block-performance-guide-crankshafts-manual-part-2/

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