Exhaust Gasket | Honda CT90 / Trail 90

Exhaust Gasket | Honda CT90 / Trail 90

The gasket between your Trail 90's cylinder head and exhaust pipe is one of those parts you forget exists — until you start hearing a ticking noise at idle. After decades of heat cycles, the original gets compressed flat and buried under carbon. A fresh gasket seals the joint and stops the leak.

Why You Need This

Tick, tick, tick — that rhythmic ticking at idle is the telltale sign of an exhaust leak at the cylinder head. Over decades of heat cycles the gasket gets crushed and carbon-fouled, so coated with soot that it blends into the port and goes unnoticed when the pipe comes off for any other service.

A leaky exhaust gasket does more than make noise. Exhaust gas escaping before the muffler costs you back pressure, which makes carburetor tuning inconsistent. Fresh gasket, proper seal, clean idle.

Specifications

Doing a full rebuild? This gasket is also included as Gasket M in our CT90 Overhaul Gasket Kit. If you're tearing into the engine, buy the kit instead of ordering pieces.

Installation

Difficulty: Beginner

1. Remove the flange nuts at the cylinder head, then loosen the muffler bracket bolts so the full exhaust comes free. Slide the pipe off.
2. Inspect the exhaust port. If you see bare aluminum, the old gasket came off with the pipe. If the port looks dark and sooty, the old gasket is still in there under a layer of carbon — scrape the carbon off with a small screwdriver until you can see the gasket underneath.
3. Carefully pry the old gasket out of the port.
4. Press the new gasket into the exhaust port.
5. Reassemble in the order the factory sequence is: fit the exhaust pipe flange to the cylinder head and start the flange nuts hand-tight. Tighten the muffler bracket bolts at the frame first, then final-tighten the flange nuts last. This sequence lets the pipe settle into position before the clamping load goes on.

Our 5 Small Maintenance Jobs Often Missed video covers exhaust gasket replacement as one of five commonly-skipped maintenance items. Demo bike is a larger CB twin, but the symptoms and remove-the-pipe-and-scrape approach are identical.

Frequently Asked Questions

How do I know if my exhaust gasket is leaking?

Listen for a ticking or hissing sound at the cylinder head at idle. You may also see black carbon deposits around the joint where the pipe meets the head. If you've had the pipes off for any reason and didn't replace the gasket, odds are good it's leaking.

Is this the same gasket that comes in the overhaul kit?

Yes. This is listed as Gasket M in our CT90 Overhaul Gasket Kit. If you're doing a full engine rebuild, the kit is the better buy. If you just need to fix an exhaust leak, this is the right part.

Does this fit my Honda ST90?

We can only confirm fitment on the CT90 K0–K9. The ST90 uses a similar 90cc engine but Honda did not publish cross-compatibility data. If you want to verify, check your existing OEM part number against 18291-028-306 before ordering.

Can I reuse the old gasket?

Once a gasket has been compressed and heat-cycled, it rarely seals properly again. A new gasket is cheap insurance against re-doing the job. Replace it whenever the exhaust pipe comes off.

You Might Also Need

• Full Exhaust Pipe & Muffler — CT90 — genuine Honda replacement for rusted-through factory pipe and muffler
• Muffler Spark Arrestor — CT90 / SL100 / SL125 — required in some states and national forests
• Gasket Kit (Overhaul) — CT90 — full engine gasket set, includes this exhaust gasket as Gasket M
• Allen Bolt Kit — CT90 — stainless Allen-head upgrade for the factory Phillips/hex hardware

Last updated: April 2026