| Tools Needed | Quantity | |
| 193-5859 | Cylinder Pressure Gauge Gp (Gas Engine) | 1 |
Cylinder pressure can be measured during inspection of the spark plugs. The condition of the following items can be tested by checking the cylinder pressure: valves, valve seats, pistons, piston rings, and cylinder liners.
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
Measure the cylinder pressure of an engine after approximately 250 hours of operation. Record the data. Continue to measure the cylinder pressure periodically. 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. Refer to Operation and Maintenance Manual, "Overhaul (In-Frame)".
If the cylinder pressure has risen by one or more compression ratios, the engine needs a top end overhaul 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, use the 193-5859 Cylinder Pressure Gauge Gp (Gas Engine). Use the Special Instruction, NEHS0798 that is included with the gauge. Use the following guidelines:
- Remove all the spark plugs.
- Fully open the throttle plate.
- Minimize the cranking time. This action will enable a maximum consistent cranking speed for the check. Also, the battery power will be conserved.
Illustration 1 is a graph of typical cylinder pressures for engines with different compression ratios.
Note: The 0-phase effective compression ratio is 8.5:1.
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| Illustration 1 | g00828960 |
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(Y) Cylinder pressure in kPa
(X) Compression ratio (1) Normal range for cylinder pressure | |