There are four steps to diagnosing engine noise. You must
determine the following conditions:
| • | Determine the exact operating condition under which the noise
exists. |
| • | At what rate, and at what location in the engine. |
| • | Compare sounds in other engines to make sure you are not trying
to correct a normal condition. |
Identify the type of noise. For example, a light rattle or low rumble.
Remember, engine noises are generally synchronized to either engine
speed (caused by the crankshaft, connecting rods or pistons) or one-half engine
speed (valve train noise). Try to determine the rate at which the noise is
occurring.
| • | Engine flywheel contacting the splash shield. Reposition the splash
shield. |
| • | Loose or broken crankshaft balancer or drive pulleys. Tighten
or replace as necessary. |
| • | Excessive piston to bore clearance. Replace the piston. |
| • | Cold engine knock usually disappears when the specific cylinder
secondary ignition circuit is grounded out. Cold engine piston knock which
disappears in 1.5 minutes should be considered acceptable. |
| • | Improper oil viscosity. Install recommended oil viscosity for
expected temperatures. |
| • | Excessive piston to bore clearance. |
| • | Excessive piston pin to piston clearance. |
| • | Excessive crankshaft end clearance. |
| • | Excessive crankshaft bearing clearance. |
| • | Detonation or spark knock. Check operation of ignition controls
or knock sensor circuit. |
| • | Loose torque converter bolts. |
| • | Exhaust leak at manifold. Tighten the exhaust manifold bolts and/or
replace the gasket. |
| • | Excessive connecting rod bearing clearance. Replace bearings as
necessary. |
| • | Excessive piston pin clearance. |
| • | Excessive crankshaft thrust bearing clearance. |
