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Generac GT-990 — Check and Adjust Valves

Adjustments · Engine valves

For the Generac GT-990, from the Generac service manual.

Applies to: Generac GT-990 engine

Procedure

  1. Make sure the piston is at Top Dead Center of its compression stroke (both valves closed).
  2. Remove the four (4) screws from the rocker cover.
  3. Remove the rocker cover and rocker cover gasket.
  4. Loosen the rocker arm jam nut. Use a 10mm allen wrench to turn the pivot ball stud.
  5. Check the clearance between the rocker arm and the valve stem with a flat feeler gauge.
  6. When the valve clearance is correct, hold the pivot ball stud with the allen wrench and tighten the rocker arm jam nut.
  7. Torque the jam nut to 174 inch pounds, then recheck the valve clearance.
  8. Re-install the rocker cover gasket, rocker cover and the four (4) screws.

Tools required

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • Valve clearance 0.05-0.1 mm (0.002-0.004 in.) cold
  • Rocker arm jam nut torque 174 inch pounds

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.

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