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Engine Kits Combine Frequently Replaced Parts


6/20/2013
By Larry Carley

Engine kits typically combine all of the frequently replaced parts such as bearings, rings and gaskets, and may include pistons, valve springs and other parts depending on the type of kit.
 
Engine parts are not a fast-moving product category, but are very important nonetheless. A customer may need one or more internal engine parts to fix a problem or to overhaul an engine. Engine kits typically combine all of the frequently replaced parts such as bearings, rings and gaskets, and may include pistons, valve springs and other parts depending on the type of kit.

Standard crankshaft bearings can restore oil clearances and oil pressure provided the crank journals are not damaged or heavily worn. But if the crank journals are rough, out-of-round, tapered or scored, or the crank has spun a bearing, a reground crankshaft with undersized journals and matching bearings will be required to restore proper oil clearances. Bearing clearances should always be checked by measuring or with Plastigage to make sure they are correct when an engine is put back together.

Piston rings also can be confusing to replace. Many engines that have the same bore and stroke have been equipped with different piston and ring combinations. Replacement rings for standard pistons must have the same thickness, depth and diameter as the original rings. If the engine’s cylinders have been bored to oversize to compensate for wear or damage, then oversized pistons and matching rings are required. Replacement pistons also should match the original piston’s compression ratio and crown configuration with valve reliefs cut in the same locations. Higher compression pistons are a popular upgrade for performance applications, as are stronger forged pistons. Assembly tolerances may differ when making such changes so make sure your customer is getting the correct pistons for his engine.

Worn camshafts have become a more common problem in recent years, mostly in older vehicles with flat tappet camshafts. The reason why this is occurring is that the amount of ZDDP anti-wear additive in motor oil has been substantially reduced to prolong the life of catalytic converters and oxygen sensors (both of which can be fouled by the phosphorus in ZDDP). Late-model engines with roller cams or OHC cam followers can get by with little ZDDP in the oil, but not so for older engines — especially if they have been modified with a performance cam and/or stiffer valve springs. So, if a customer is replacing a flat tappet cam in an older engine, advise him to use plenty of assembly lube on the cam lobes and lifters, and to use a ZDDP oil supplement to protect the new cam from wear.

Also, flat tappet cams and lifters should be replaced as a set. Installing a new cam with worn lifters or vice versa increases the risk of cam or lifter failure. New valve springs also are recommended for high-mileage engines when changing a cam. And if the springs are stiffer than the original springs (higher seat and open pressure), stronger pushrods are also recommended.

Lastly, don’t forget the oil pump. The oil pump is the only internal engine component that runs on unfiltered oil. Housing and gear wear is common in high-mileage pumps and can cause a drop in oil pressure. Recommend a new oil pump and pickup screen for high-mileage engines that are having other internal parts replaced.












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