In our September issue, Steve Dulcich began answering Lawren Minor's question of what he should know about basic engine rebuilds. In the first installment, Steve covered basic block machining and preparation, proper reconditioning of cylinder heads, how to choose the right crankshaft, and basic rod and piston configurations. In this, the second installment, Steve covers proper piston-ring selection, camshafts, quench, and engine balancing.
Rings may all look similar, but the difference in materials makes a difference in performa
Two things to consider when choosing a set of rings are size and type. Size is simple; they have to fit the bore and the pistons. Type refers to material and coatings. Cast-iron is the entry-level ring-the kind you get in a cheap remanned engine or a discount rebuild kit. Plain cast-iron rings were used in most stock Mopar engines, and like the stockers, they usually wear out the bore in 100,000 miles. Moly rings are the type favored by engine builders and OEM manufacturers today. The moly face of the ring conforms better to the cylinder bore and retains a wick of oil, which helps bore life considerably.
Moly isn't a ring material itself, but it is applied to the ring in a receiver groove or coated over the full face of the ring. Better moly rings are based on a ductile-iron ring body, which is superior to the standard-iron ring material, particularly in extreme applications.
File-fit rings are individually fitted to each bore for optimal endgap, capturing as much
Chrome-faced rings are as the name implies-chromed on the face, giving the ring a hard wear surface. Chrome rings were once quite popular, but slow break-in on the chrome and advancements in moly-ring technology have made chrome the less desirable choice.
Rings can be acquired in standard-fit or file-fit sizes. They have an open end, and when installed, there is a gap. This gap is open to compression leakage, and in a high-performance engine, minimizing the running gap of the ring pays off measurably in power. Pregapped or standard-fit rings have somewhat more than ideal endgap, but usually drop into a specified bore size without additional work. File-fit rings are made a few thousandths-inch larger in diameter and are filed on their ends to provide the exact endgap the engine builder is after. File-fit rings add to the work of putting an engine together, but there is some power to be had.
To get the cam timing events occurring at the designed specifications, the cam should be d
Camshafts can be sorted by type in two ways: Some camshaft lifters have a roller at the end (roller cam); others have a flat face (flat tappet). Also, some are solid-lifter designs, and others incorporate a hydraulic adjustment mechanism. Factory Mopar cams from the musclecar era were predominantly hydraulic flat tappets, yet a notable number of engines came with solid flat tappets. Hydraulic rollers appeared in Mopar OE engines in 1985, and these days, nearly all newer engine designs use this type of cam and follower. Hydraulic flat tappets are simple to install, require no adjustment once the engine is built, and are quiet in operation. Hydraulic cams get their name from the hydraulic mechanism designed into the lifter. An oil-filled plunger in the lifter body self-adjusts to remove any slack in the valvetrain. Hydraulic rollers share all these features, but the roller follower allows the cam lobe to be designed with a faster-opening profile, and it produces less friction.
Solid cams do not have the hydraulic mechanism in the lifter to remove the clearance from the valvetrain. Instead, a small amount of clearance must be set in the valvetrain to ensure the valves will close as the lifter comes off its lobe. This is valve lash, and it needs to be adjusted periodically to maintain the correct clearance specification. A hydraulic lifter's hydraulic mechanism has an increasingly difficult time maintaining control as rpm rises because the internal plunger can overextend, or, at times, bleed down.