Chevrolet Small-Block Parts Interchange Manual - Revised Edition. Ed Staffel

a thin parting line on its throw arms, while a forged crank has a much thicker or wider parting line.

      Check the casting number and casting dates to determine what stroke it is. Does it use a one-piece or two-piece rear main oil seal? Measure the rod and main journals. Has the crank been previously cut down? Machine shops that recondition cranks usually stamp the amount they have cut the crank on the front crank throw arm. If your measurements show that the crank journals have been previously cut more than 0.010 inch, walk away. You can find another one.

      Are the threaded holes in the rear flange stripped? Has the drilled hole for the pilot bearing at the rear of the crank been elongated or damaged? Has the thrust surface on the crank been worn or damaged? How about the threaded hole in the crank front snout? Some early crank snouts are not drilled or tapped for a vibration damper retention bolt. You can get the snout tapped and threaded for the bolt at a machine shop. Also, some early cranks that were used in automatic transmission cars did not have a hole drilled in the rear of the crank for a manual transmission pilot bushing.

      Remember, when you get the crank to the machine shop, ask the crew to clean it, check for cracks and straightness, clean out the threaded holes and oil passages, and possibly have it ground and micropolished. If any of the journals have been damaged, you may be able to have the journal welded or chromed then cut back to acceptable size. However, you need to compare the cost of fixing a damaged crank to the cost of buying an undamaged one. At some point, it’s cheaper and easier to find an undamaged used crank or to buy a new one than to repair a damaged one.

      Check the crank journal diameters to see if the crank has been previously cut and to determine the size of the bearings you need.

Cast Versus Forged Cranks

      Chevy stock cranks are either nodular cast iron or forged steel. To figure out which yours is, check the parting line, which is left from the molds when the crank is poured. A cast crank has a thin parting line, while a forged crank line is thicker or wider. Tap a crank lightly with something hard, and a cast crank emits a thudding noise. A forged crank rings like a bell; it is a quite distinctive sound. Of course, you can also check the casting number.

      Some people who build high-performance motors believe that they must have a forged crank and that cast cranks just don’t cut the mustard. They would rather shell out the extra money for a forged crank.

      The truth of this belief depends on your situation. Up to a point, cast cranks are fine. In a short-duration, normally aspirated bracket drag race engine, 450 genuine horsepower is around the upper limit for

      A cast crank can be distinguished from a forged crank by its thinner parting line.

      Notice the thicker parting line of this 350 forged crank. a small-block cast crank. Almost any true street-cruising application can get along just fine with a cast crank. At horsepower levels higher than 450, or if you are planning a nitrous or high-boost blower or turbo application, move to a forged steel crank.

      Good used cast cranks are more numerous and less expensive than forged cranks. You can take the money you saved and spend it on something else. Just be sure the crank is magnafluxed and properly prepped and use a high-quality vibration damper (especially with a cast crank).

      These days, a large number of forged cranks are available from aftermarket suppliers for a large range of applications, stroke lengths, steel alloys (most use a very strong 4340 alloy), and total weights. These aftermarket cranks can also be prepared in various ways. All of the counterweights can be knife-edged to reduce weight and windage. The crank pins on the rod journals can be drilled to further reduce weight. Extra-wide radius journal fillets add strength. Counterweights can be reduced in radius to reduce rotating mass. Special coatings are available that reduce oil cling, and chemical, vibration, and heat treatments are available that further harden and relieve the metals.

       Crank Stroke and Journal Sizes

      Crank strokes with small journals (2.30-inch mains/2.00-inch rods) include the 3.00-inch strokes on the Gen I 265, 283, and the 1967 302 Z28 engines. The 3.25-inch stroke lengths were used on 327s from 1962 through 1967 with small journals. The 5.7-inch rods with small rod journals and 11/32-inch rod bolts were used with these cranks.

      Strokes with medium-size journals (2.45-inch mains/2.10-inch rods) include the 1968 to 1969 302 Z28 with a 3.00-inch stroke, a 3.10-inch stroke used on the 262, 3.25-inch used on the 307 and 1968 327s, and 3.48-inch strokes on the 267, 305, and 350. The Gen II 265-ci V-8 uses these journal sizes with a 3.0-inch stroke and one-piece rear main oil seal. The 5.7-inch rods with 2.10-inch rod journal sizes are used with these medium journal cranks with the exception of the Gen II 265 L99 motor, which uses a 5.940-inch rod. Production rods for medium-size journals have 3/8-inch rod bolts.

      The 400 used a 3.75-inch stroke with larger main journal diameters of 2.65 inches and rod journals of 2.10 inches. The 400 uses a shorter 5.565-inch length rod with 3/8-inch rod bolts. These 400 rod bolts have a unique head on the bolt, which helped provide more clearance between the bolt head and cam lobes and the block itself.