Applicable Models

K4 | K5 | K6 | K7 (1976) | K8 (1977) | K9 (1978) | K10 (1979)

Note: The CTK0 - K3 uses a hydraulic only cam chain tensioner that does not need adjustment.

What is the recommended interval for setting the cam chain tension?

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)

You may frequently hear us mention the "core tune-up procedure." When we refer to this, we are talking about three key procedures from the Honda service manual for the CT90: cam chain tension, valve adjustment, and ignition timing. Performing these procedures in the correct order is crucial for ensuring the motorcycle starts on the first kick and revs smoothly to redline. Trail 90s are designed to run hard, often near full throttle, so it’s important to establish a solid foundation with a perfectly tuned engine from the start.

Cam chain adjustment is the first step in the process because it directly affects both valve adjustment and ignition timing. This procedure ensures the cam chain— which connects the camshaft to the crankshaft—remains properly tensioned. Maintaining the correct tension eliminates excess slack, allowing the valve train, crankshaft, and ignition system to stay in proper alignment.

Static Cam Chain Adjustment

The Honda service manual recommends adjusting the CT90 cam chain tension while the engine is running. However, excessive play in the cam chain can make it difficult to start the motorcycle. If the motorcycle has gone a long time without adjustment, the chain may have significantly more slack than usual. In our companion video, you can see the excessive play in the cam chain on the magnetic rotor behind the inspection cover. To address this, we will first make a static adjustment to remove most of the slack. Once the valve clearances are set, the ignition timing is adjusted, and the engine is running, we will return to properly tension the cam chain as outlined in the manual. If you find that you do not have this large amount of slack in your engine, skip this step and set the cam chain tension while the engine is running from the start. 

To set the cam chain tensioner you will:

1. Remove the rotor / inspection cover
2. Remove the spark plugs
3. Turn the engine over until you have the engine set at Top Dead Center on the compression stroke. 
4. Below the inspection cover, you will find the cam chain tensioner lock screw and jam nut as well as the tensioning screw underneath the dust cover on the bottom of the engine.
5. Loosen the jam nut on the lock screw and back out the screw for 3-4 turns. If you are way out of adjustment, you will hear the spring-loaded piston spring forward to take up the excess play in the system. 
6. Lightly turn the tensioning screw with a small screwdriver until you just barely feel resistance. 
7. Once there is resistance, tighten the lock screw until it stops and hold the screw in place with a flat head screwdriver while the jam nut is getting tightened. 
8. Reinstall the dust cover over the tensioning screw. Replace the sealing washer if its in rough shape.
9. The tension is now good enough to do the remaining valve and ignition timing.

Running Cam Chain Adjustment

To set the cam chain tensioner you will:

1. 1. Start the motorcycle and let it warm up for a minute.
   2. Below the inspection cover, you will find the cam chain tensioner lock screw and jam nut as well as the tensioning screw underneath the dust cover on the bottom of the engine.
   3. Loosen the jam nut on the lock screw and back out the screw for 3-4 turns.
   4. Lightly turn the tensioning screw with a small screwdriver until you just barely feel resistance. 
   5. Once there is resistance, tighten the lock screw until it stops and hold the screw in place with a flathead screwdriver while the jam nut is getting tightened. 
   6. Reinstall the dust cover over the tensioning screw. Replace the sealing washer if its in rough shape.
   7. The tension is now completely set.