Generac — Test 38 - Check Engine/Cylinder Leak Down Test / Compression Test
Testing & diagnosis · engine cylinder
From a Generac service manual covering: 4700, QuietPact 40, QuietPact 40 LP, QuietPact 40G, QuietPact 40LP. Check it applies to your exact model before use.
Applies to: Generac 4700, Generac QuietPact 40, Generac QuietPact 40 LP, Generac QuietPact 40G, Generac GH-220 engine
Procedure
- Remove spark plug and valve cover
- Rotate crankshaft to TDC with both valves closed; lock flywheel
- Attach cylinder leak down tester adapter to spark plug hole
- Connect air source of at least 90 psi; adjust regulated pressure to 80 psi
- Read cylinder pressure gauge; 20 percent leakage is normally acceptable
- Listen for air escaping at carburetor (intake valve), exhaust (exhaust valve), or breather (piston rings)
- For compression check, insert compression gauge in spark plug hole and crank engine until pressure stops increasing
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Minimum allowable compression pressure, cold engine: 60 psi
Full service-parts list: Generac 4700 →, Generac QuietPact 40 →, Generac QuietPact 40 LP →, Generac QuietPact 40G →
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.