Clutch Friction Disc | Honda CT90 / Trail 90
If your Trail 90 revs up but won't pull — engine speed climbs but the bike barely moves — your auto clutch friction discs are worn out. The CT90's centrifugal auto clutch is a unique Honda design that engages automatically via weighted arms in the clutch basket. When the friction material wears down, the clutch slips under load. This kit replaces all three friction discs to restore proper clutch engagement.
Why You Need This
The CT90 / Trail 90 uses a semi-automatic centrifugal clutch — not a hand-operated manual clutch like the CB350 or CB450. The auto clutch relies on centrifugal force from weighted arms in the clutch basket to squeeze the friction discs and steel plates together. The faster the engine spins, the more force is applied. When the friction material wears thin, the clutch can no longer grip under load — you'll feel it slip during acceleration or at higher speeds.
This kit includes three identical replacement friction discs for the CT90 auto clutch. The clutch springs are not included — originals are typically well within service limits and can be reused. If you're experiencing clutch slip, check your oil first: synthetic or semi-synthetic oil will cause the friction discs to slip even when they're new. Use conventional mineral oil with a zinc additive.
Specifications
| Spec | Detail |
|---|
| Replaces OEM Part Numbers | 22201-121-631, 22201-096-000, 22201-121-306, 22201-121-690 |
| Fits Models | CT90 K0–K9 (1966–1979), CT200, CT110 |
| Clutch Type | Centrifugal auto clutch (semi-automatic) |
| Friction Disc Thickness (new) | 2.8–2.9 mm (0.110–0.114 in.) — Honda factory spec |
| Friction Disc Service Limit | 2.4 mm (0.094 in.) — replace if below |
| Steel Plate Thickness (new) | 1.93–2.07 mm (0.076–0.082 in.) — Honda factory spec |
| Steel Plate Service Limit | 1.85 mm (0.073 in.) — replace if below |
| Kit Contents | 3 friction discs (identical, symmetrical) |
| Sold As | Set of 3 discs — one set rebuilds one clutch |
Note: The CT90 auto clutch has 4 steel plates and 3 friction discs. The 4 steel plates are each unique — they must be installed in the correct order. The 3 friction discs are all identical and can go in any position.
Important — oil type matters: Do NOT use synthetic or semi-synthetic engine oil in the CT90. Synthetic oil causes clutch friction discs to slip, even when new. Use conventional mineral oil (such as 15W-40 diesel truck oil — make sure it's full mineral, not semi-synthetic) with a zinc additive.
Installation
Difficulty: Intermediate
- Drain the engine oil — 17mm drain plug. The CT90 holds just under 1 quart.
- Remove the right side engine cover — Remove the clutch adjustment cover, nut, and O-ring first, then the cover bolts.
- Remove the auto clutch mechanism — Detach the shift arm and ball lifter assembly. Note the orientation of all parts.
- Remove the clutch basket — You'll need the Oil Filter Nut Tool (SKU 9005) for the four-prong nut. Bend down the lock tabs first. An electric impact makes removal much easier.
- Disassemble the clutch on the bench — Remove the snap ring, then carefully remove steels and friction discs, noting the exact order. There are 6 springs (4 long, 2 short) on posts between the plates.
- Clean everything — Clean the clutch basket inside and out, the lower crankcase, the oil pickup screen, and the centrifugal oil filter inside the clutch basket.
- Soak new friction discs in oil — Submerge in 10W-40 conventional motor oil before installation. Do NOT use synthetic.
- Reassemble in correct order — Steel plates must go back in the exact same sequence. Each steel is unique (different tab patterns). Friction discs are identical and go between the steels.
- Reinstall clutch basket — Torque the four-prong nut to 60 ft/lbs. Bend the lock tabs back into place.
- Adjust the clutch — Turn the adjuster screw counterclockwise until firm, then back off approximately 1/8 turn. Verify by checking play on the shift pedal. Fine-tune after riding.
Steel plate order tip: The 4 steel plates have different tab patterns — one has pins, one has notched tabs, one has alternating notches and holes, and one has all holes. Pay close attention during disassembly and keep them in order. Assembled wrong, the clutch will not work.
Our full CT90 centrifugal auto clutch rebuild video walks through every step — from draining the oil to adjusting the clutch after reassembly.
Frequently Asked Questions
How do I know if my CT90 clutch needs rebuilding?
The most common symptom is slipping under load — the engine revs up but the bike doesn't accelerate proportionally, or speed plateaus even though the engine is climbing in RPM. You may also notice it struggling to move from a stop.
I just put in new friction discs and the clutch is slipping — what's wrong?
Check your oil. Synthetic or semi-synthetic engine oil will cause friction discs to slip even when brand new. Drain it and replace with conventional mineral oil plus a zinc additive. Ride the bike for a while — the discs may recover once exposed to the correct oil.
Are the steel plates included in this kit?
No — this kit includes the 3 friction discs only. The 4 steel plates are typically reusable. Measure them with a micrometer — the Honda service limit is 1.85 mm. If any are warped or gouged below service limit, they'll need to be sourced separately.
Does this fit the S90 or CL90?
The S90 and CL90 use a manual clutch — a completely different design from the CT90's centrifugal auto clutch. These friction discs are specifically for the CT90 auto clutch mechanism.
Do I need to remove the entire clutch basket to replace the friction discs?
Yes. The clutch basket must come off the crankshaft and be disassembled on the bench. This is necessary to properly clean the basket, inspect the steel plates, and reassemble everything in the correct order.
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Last updated: March 2026
