Cummins/Onan — Cylinder Compression Test

Testing & diagnosis · Cylinders, pistons, rings, valves

From a Cummins/Onan service manual — check it applies to your exact model before use.

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Procedure

1. Start the generator set and allow it to warm up.
2. Stop the set; remove and inspect the spark plugs.
3. Insert a compression gauge in one spark plug hole.
4. Place the throttle and choke in the full open position.
5. Crank the engine and note the compression reading.
6. Stop cranking and repeat for the other cylinder.
7. Compare readings to the Specifications section.

Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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