Generac — Cylinder Leak Down Test Procedure
Testing & diagnosis
From a Generac service manual covering: GN-190, GN-191, GN-320, GN-360. Check it applies to your exact model before use.
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Before you start
- If leaking into intake or exhaust port, check lash, valve face, and seat condition.
Procedure
- Piston must be at TDC.
- Install the tester into the spark plug hole.
- Pressurize the cylinder to 90 psi.
- Observe the leakage of the cylinder and where the air is coming from.
Tools required
- Cylinder leakdown tester Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Pressurize to 90 psi
- 0-10% cylinder is good
- 10-30 FridayParts $28.40% there may be a problem
- 30-100 FridayParts $75.25% cylinder requires repair
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.