Measure the cylinder pressure of new engines. Record the data. Continue to measure the cylinder pressure. Comparing the recorded data to the new data provides information about the condition of the engine.
Note: Cylinder pressure is one of the three factors that help to determine the in-frame overhaul interval. For more information, refer to this Operation and Maintenance Manual, "Overhaul (In-Frame)" (Maintenance Section).
Cylinder pressure can be measured during inspection of the spark plugs. Use the following guidelines for checking the cylinder pressure:
- Remove all of the spark plugs.
- Verify that the choke is fully open.
- Minimize the cranking time. This procedure will enable a maximum consistent cranking speed for the check. Also, the starting air or battery power will be conserved.
A loss of cylinder pressure or a change of pressure in one or more cylinders may indicate the following conditions. These conditions may indicate a problem with lubrication:
- Excessive deposits
- Guttering of valves
- A broken valve
- A piston ring that sticks
- A broken piston ring
- Worn piston rings
- Worn cylinder liners
If the cylinder pressure has risen by one or more compression ratios, the engine needs a top end overhaul in order to remove deposits. Failure to remove the deposits will increase the chance for detonation. Severe guttering of the valves will occur.
To measure the cylinder pressure, refer to Special Instruction, GMG00694, "Analyzing Cylinder Condition By Measuring Air Flow". Also, use the 146-2739 Cylinder Pressure Adapter.
Illustration 1 is a graph of typical cylinder pressures for engines with different compression ratios.
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| Illustration 1 | g00789376 |
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(Y) Cylinder pressure in kPa (psi)
(X) Compression ratio (1) Normal range for cylinder pressure | |
Record the pressure for each cylinder. Use Operation and Maintenance Manual, "Valve Data Sheet" (Reference Materials Section).