Sample Review Questions:
1. A possible cause of low oil pressure could be:
a. Worn oil pump
b. Worn engine bearings
c. Bad oil pressure sending unit
d. Any of the above
2. A “timing chain set” typically includes:
a. New timing chain and camshaft gear
b. New timing chain and crankshaft gear
c. New timing chain, camshaft and crankshaft gears
d. New timing chain and gaskets
3. All of the following statements about timing belts are true EXCEPT:
a. Timing belts usually stretch with age
b. A broken timing belt can damage valves in an interference engine
c. Timing belts should be replaced at a recommended mileage interval to reduce the risk of belt failure
d. Replacement timing belt must be the same length as the original
4. Detonation (spark knock) can damage which of the following engine parts?
a. Piston rings and pistons
b. Head gasket
c. Connecting rod bearings
d. Any of the above
ANSWER KEY
1D, 2C, 3A, 4D
EXPLANATIONS:
1. The oil pump pulls oil from the oil pan to lubricate the engine. The pump may be mounted in the crankcase and driven off the distributor, or mounted inside the front timing cover and driven off the crankshaft. Worn pump gears or an obstructed pickup screen can cause low oil pressure.
The clearance between the crankshaft main and rod bearings and the crank journals can reduce oil pressure if the assembled clearance is too great, or the bearings are worn.
The oil pressure sending unit is mounted on the engine, and sends an oil pressure signal to the instrument panel or oil pressure gauge. A faulty sending unit may cause low readings.
2. A steel timing chain, rubber timing belt or timing gears are used to drive the camshaft(s). In engines with timing chains, there is a small drive sprocket on the crankshaft, and a larger sprocket on the end of the camshaft. The teeth on the sprockets can wear as the engine accumulates miles, and the chain may stretch, causing retarded ignition and valve timing as well as noise. So all three components should be replaced at the same time. Timing sets include a new chain and both sprockets. On OHC engines, the kit may also include new chain guides. Gaskets are sold separately in a gasket timing set.
3. Rubber timing belts are used on many overhead cam engines because they are quieter (and cheaper) than chains. Reinforcing cords inside the belt prevent it from stretching, but the rubber belt can flake and crack with age. The recommended replacement interval on many older engines is 60,000 miles, or 100,000 miles on late model engines.
A timing belt failure on an interference engine can bend valves, but should not cause any valve damage on engines that have adequate clearance between the valves and pistons.
A replacement timing belt must be the exact same length as the original, with the same number and type of teeth. A timing belt kit may include new idler/tensioner pulleys. Drive pulleys are usually not replaced unless worn or damaged.
4. Detonation (spark knock) is an erratic form of combustion that produces hammer-like blows on the pistons. The sharp rise in combustion pressure can crack pistons and rings, crush rod bearings, and crack combustion chamber armor on head gaskets. The underlying cause of the detonation problem should be diagnosed and repaired before parts are replaced to prevent a repeat failure.
Common causes include engine overheating, defective EGR system, defective knock sensor, carbon buildup in combustion chambers or low octane gasoline.
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