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ASE P2 TEST PRIMER: Engine Mechanical Parts


10/18/2013
By Larry Carley

To find the correct replacement parts, you must know the vehicle year, make and model, engine displacement in cubic inches (CID) or liters (L), and often the engine code or vehicle identification number (VIN).
 

Major engine components include the block, cylinder heads, crankshaft, main and rod bearings, connecting rods, pistons and rings, oil pump, timing gears, timing chains, timing belts, camshaft, lifters (roller and flat tappet, solid and hydraulic), pushrods, valves (intake and exhaust), valve springs, valve guides, valve seals, valve seats, valve spring retainers, rocker arms, cam followers, intake and exhaust manifolds, head gaskets, pan and cover gaskets, intake and exhaust manifold gaskets, flywheel and harmonic balancer.
Replacement engine parts may be sold individually, in sets, or in complete overhaul kits. Ditto for gaskets and gasket sets.

To find the correct replacement parts, you must know the vehicle year, make and model, engine displacement in cubic inches (CID) or liters (L), and often the engine code or vehicle identification number (VIN).

Components that may need to be replaced in a high-mileage engine include the oil pump (and pickup), valve guides and seals, rod and main bearings, piston rings, timing chain and gears, camshaft and lifters (should be replaced together), and valve springs.

In overhead cam (OHC) engines that use a rubber timing belt rather than a timing chain to drive the cam(s), there is usually a recommended replacement interval (60,000 to 100,000 or more miles depending on the application). This is essential maintenance because if a timing belt fails in an “interference” engine (one with close piston-to-valve clearances), it will cause expensive engine damage.

In pushrod engines, the camshaft is mounted in the engine block rather than the cylinder head, and is driven by a set of gears or a timing chain. Timing chains can stretch at high mileage, but have no specified replacement interval. A worn timing chain can make noise from the front engine cover, and cause retarded valve and ignition timing (hurts performance). Replace worn timing chains and gears at the same time with a new timing set.

Crankshaft bearing clearance is critical for good oil pressure. Worn bearings can cause engine noise, low oil pressure and may result in engine failure. Replacement bearings must be the correct size for the crankshaft journals. Reground crankshafts require undersized bearings. Installed bearing clearances should always be checked with Plastigage or a feeler gauge.

Worn piston rings cause a loss of compression and increased oil consumption. Cylinders need to be deglazed with a honing tool if rings are replaced, and rings must be installed on pistons using a ring expander to avoid damaging the rings.

Another common cause of high oil consumption is worn valve guides and seals. Most cast iron cylinder heads (except on big block Chevys) have integral valve guides, while aluminum heads have replaceable cast iron or bronze valve guides.

If a flat tappet camshaft is being replaced, the lobes must be coated with a high-pressure assembly lube. A motor oil (or oil supplement) containing the anti-wear additive ZDDP also is recommended to reduce the risk of cam lobe and lifter wear.

Required to pass this section of the P2 test:
1. Identify major engine components.
2. Identify component function and common reasons for replacement.
3. Identify related items, including gaskets, motor oils, service chemicals and tools.
4. Provide basic use, maintenance, installation, and warranty information.













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