Generac — Adjusting GH-410/GT-990 Valve Clearance
Adjustments · Engine
From a Generac owner's manual — check it applies to your exact model before use.
Applies to: Generac GT-990 engine, Generac GH-410 engine
Before you start
- Hold the rocker arm jam nut in place as you turn the pivot ball stud.
Procedure
- Make sure the engine is at room temperature.
- Remove the spark plug wire from the spark plug.
- Remove the four screws attaching the valve cover.
- Set the piston at Top Dead Center of its compression stroke.
- Loosen the rocker jam nut; turn the pivot ball stud; check clearance with a feeler gauge.
- Tighten the rocker arm jam nut to 174 in/lbs.
- Install a new valve cover gasket and re-attach the valve cover.
- Re-attach the spark plug wire; on GT-990 repeat for the other cylinder.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Valve clearance 0.002-0.004 inch (0.05-0.1 mm)
- Rocker arm jam nut torque 174 in/lbs
Source: Generac owner's 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.