See Figure 1
A noticeable lack of engine power, excessive oil consumption and/or poor fuel mileage measured over an extended period are all indicators of internal wear. Worn piston rings, scored or worn cylinder bores, blown head gaskets, sticking or burnt valves and worn valve seats are all possible culprits here. A check of each cylinder's compression will help you locate the problems.
As mentioned in Tools and Equipment in General Information & Maintenance , a screw-in type compression gauge is more accurate than the type that you simply hold against the spark plug hole, although it takes slightly longer to use. It's worth it to obtain a more accurate reading. Engine compression is checked in the following manner:
- Warm up the engine to normal operating temperature.
- Tag the plug wires and remove all spark plugs.
- Disconnect the high tension lead from the ignition coil.
- On carbureted cars, fully open the throttle either by operating the carburetor throttle linkage by hand or by having an assistant floor the accelerator pedal. On fuel injected cars, disconnect the cold start valve and all injector connections.
- Screw the compression gauge into the No.1 spark plug hole until the fitting is snug.