For years, factory cranks were about the only choice for anything but an all-out race-engine build. These days, there is a variety of aftermarket replacement and race cranks available. One advantage of going new is the crank hasn't been subject to fatigue, and metal fatigue leads to crank failure. The crankshaft is subject to repeated load and unload stress cycles and has a finite fatigue life based on the number of cycles and load. Although it may seem fine through a typical magnaflux inspection, a crank that has seen severe duty over a long period of time may be near the point of fatigue failure. Aftermarket crankshafts can be had in various grades of iron and steel, constructed from castings, forgings, or billet to suit practically any need or budget. There are also several stroker-style cranks available for both big- and small-block Mopars. A stroker crank increases the stroke of the engine, adding significantly to the cubic-inch displacement. Strokers have become popular in performance-engine building; after all, as the saying goes, there's no substitute for cubic inches.
Aftermarket stroker cranks have become popular, opening the door for a whole new world of
We discussed in detail pistons and piston choices in "Piston Science" elsewhere in this issue, so we'll touch on the basics here. Like crankshafts, pistons are manufactured by either the forging or casting process, and again, forging gets the nod in durability. Various grades of aluminum are used in both forged and cast pistons, again delineating the grades of durability. Pistons will be part of the process if an engine is being rebuilt, and it pays to anticipate future mods when making a selection. Building a mild 440? Who knows, maybe a little nitrous will be in the cards a few years down the road for a little added oomph. About that time, you'll be glad you stepped up to a set of forged slugs instead of the cast cheapies.
There is a variety of design specifications available in pistons, the most important of these being the compression height and head configuration. Compression height basically determines how high the piston ends up at TDC, which is important for compression ratio as well as clearance. Piston-top configuration varies greatly, depending upon the requirements of the engine. Dished pistons have a depression built into the top of the piston to lower compression ratio. Flat-top pistons are simply flat across the top; although valve notches are incorporated into high-performance designs to provide clearance for high-lift and long-duration cams. Domed pistons actually rise up into the combustion chamber to squeeze at a higher compression ratio. Reverse dome or kick-up quench dome pistons are designed to provide a proper quench clearance in an open-chamber head.
Most stock engines use pressed piston pins. Machine shops generally install the pistons to
Some other points to ponder include the piston-ring size for which the ring lands are cut. Stock engines used 5⁄64-inch thick compression rings, while thinner 1⁄16-inch compression rings have long been popular in performance application, and thinner rings are now widely used by OEM manufacturers. The piston determines the ring thickness, so be aware when ordering parts. Pistons can be fitted to the rods with the pin pressed into the rod, or floating with the pin retained by locks at the end of the piston's pin bore. If rods designed for floating pins are used, get pistons machined with grooves to accept locks.
Rodin' At Random
Connecting rods connect the pistons to the crank, and they take some abuse in a high-performance engine. If the stock rods are being reused in a rebuild, the rod's bearing bore at the big end (crank) is checked for roundness and size. If outside of specification, the rod and cap can be ground slightly at the parting surface, and the bore honed to resize the rods. New high-strength aftermarket bolts are often installed during the process. Some Mopar engines, such as early small-blocks, used floating piston pins, which ride on a bronze bushing in the small end. These bushings need to be checked for wear and often need replacing.