Applicable Models

All CT90 Models

What is the recommended interval for setting the valve clearances?

The Honda Recommended Valve Adjustment Interval: 2,400 - 3,000 miles (4,000 - 4,500 km)

The CMC Recommended Valve Adjustment Interval: 1,000 - 1,200 miles (1,500 - 2,000 km)

We often refer to the "core tune-up procedure," which consists of three essential maintenance steps outlined in the Honda service manual for the CT90: cam chain tension adjustment, valve adjustment, and ignition timing. Performing these procedures in the correct sequence is critical to ensuring the motorcycle starts reliably on the first kick and accelerates smoothly to redline. Since Trail 90s are built to run hard, often at near full throttle, a properly tuned engine is key to both performance and longevity.

The second step, valve adjustment—also known as tappet adjustment—must be completed before setting the ignition timing. This procedure ensures the rocker arms ride along the camshaft lobes to open and close the valves precisely at the right moments during the engine cycle. Proper valve timing and clearance are critical for drawing in the correct volume of the air-fuel mixture and compressing it before the spark plug is triggered. It also ensures that exhaust gases exit the cylinder head at the optimal time.

Honda CT90 / Trail 90 valve clearance specification

Intake: 0.05 mm (0.002 in)

Exhaust:  0.05 mm (0.002 in)

How to set the Valve / Tappet Clearance

1. Remove the inspection cover.
2. Remove the spark plug.
3. Turn the engine over while covering the spark plug hole with your finger. When you feel air being forced out against your finger, the engine is on the compression stroke.
4. You will feel compression through the spark plug hole as you approach the T mark on the rotor. Line up the T mark on this stroke with the alignment mark on the stator coils.
5. Remove the valve covers.
6. Loosen the exhaust tappet screw lock nut.
7. CMC uses what we call the "overshoot method" when we adjust valves. This involves using a slightly bigger feeler gauge to "overshoot" the valve clearance to not accidentally set things too tight. Tight valves can break parts while loose valves just make noise. We insert a 0.003" (0.08 mm) feeler gauge in between the rocker arm pad and exhaust tip.
8. Use the CMC Valve Adjustment Wrench to loosen or tighten the adjustment screw until the feeler gauge has a tight fit but is still able to slide in and out. 
9. Bring the lock nut back down on the exhaust tappet adjustment screw and tighten it down while holding the adjustment screw in place so it does not move.
10. Go back and check your valve clearance using the correct spec valve clearance of 0.002" (0.05 mm) to ensure there is a good fit and the clearance is not set too tight.
11. Repeat the same procedure with the intake rocker arm so that it has the correct valve clearance.
12. Reinstall the valve covers.
13. Move on to the ignition timing as your final step of the core tune-up procedure. 

Parts you might need

CT90 Valve / Tappet Adjustment Wrench

Feeler Gauge Set