- A set of feeler gauges
- A 10mm wrench
- A flathead screwdriver
- A spark plug wrench
Step 1: Engine Cool Down
Remove the engine's left-side cover. Remove the spark plug from the engine.
Step 2: Engine at TDC
Turn the engine over until the piston is at the top of its compression stroke. This can be checked by inserting a screwdriver into the spark plug hole and turning the engine until the screwdriver stops rising.
Step 3: Checking Gap
Insert a feeler gauge between the rocker arm and the valve stem. The gap should be between 0.002 and 0.004 inches. If the gap is too large or too small, it must be adjusted.
Step 4: Adjusting the Gap
To adjust the gap, loosen the locknut on the rocker arm with a 10mm wrench. Then, turn the adjusting screw with a flathead screwdriver until the gap is between 0.002 and 0.004 inches. Finally, tighten the locknut.
Step 5: Valve Cover Reinstall
Replace the spark plug and reinstall the left-side engine cover.
By following these steps, you can correctly adjust the valves on a Yamaha TTR-90.
