Generac — Measuring Compression Pressure
Testing & diagnosis · Engine
From a Generac service manual covering: IM100G, IM80G, NP100G, NP80G. Check it applies to your exact model before use.
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Procedure
- Warm up the engine. Shut down and remove all spark plugs.
- Use a standard automotive type compression gauge.
- Hold the throttle and choke valves on carburetor wide open.
- Crank the engine and read the compression pressure.
- If compression is low in any cylinder, pour a small amount of clean engine oil into the cylinders through the spark plug opening and retest.
Tools required
- Compression gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Standard 192 psi (13.5 kg/cm²) at 350 rpm
- Minimum 164 psi (11.5 kg/cm²) at 350 rpm
- Difference between cylinders should not exceed 14 psi (1.0 kg/cm²)
Source: Generac 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.