Copper Exhaust Pipe Gaskets | Honda CB350 / CL350 / CB360 / CL360
Tick, tick, tick — hear that ticking sound near your cylinder head? That’s an exhaust leak. The copper crush gaskets between your exhaust ports and header pipes get compressed, carbon-coated, and eventually stop sealing. A fresh pair eliminates the leak, restores proper back pressure, and makes carburetor tuning predictable again.
Why You Need This
These copper gaskets sit in the exhaust port on the cylinder head, sandwiched between the head and the exhaust pipe flange. Over time they crush flat and get buried under carbon buildup — most people don’t even realize they’re there until the ticking starts. An exhaust leak at the port throws off your air/fuel mixture and can make tuning frustrating. The exhaust pipes come on and off these bikes frequently during restoration work, and every time they do, the gaskets take a hit.
These copper replacements crush and conform when you tighten the exhaust flange, forming a tight seal against the cylinder head port. Done right, they can actually be reused three to four times before they need replacing again.
Specifications
| Spec | Detail |
|---|
| OEM Part Numbers | 18291-286-306, 18291-286-000 |
| Fits Models | CB350 K0–K5 (1968–1973), CL350 K0–K5 (1968–1973), SL350 K0–K2 (1969–1973), CB360G (1974), CB360T (1975–1976), CL360 K0–K1 (1974–1975), CJ360T (1976–1977) |
| Material | Copper |
| Sold As | Pair (two gaskets — one per cylinder) |
Note: Sold as a pair. Two exhaust gaskets are needed per bike — one for each exhaust port. Get some extras while you’re ordering; you’ll use them.
Note: The CB450 and CB500T have a different exhaust port diameter and use a different copper gasket — see our CB450 / CB500T Copper Exhaust Gaskets. Do not use this gasket on a CB450 or CB500T.
Installation
Difficulty: Beginner
Tools needed: 12mm wrench or socket, small flathead screwdriver
- Unbolt the 12mm nuts on the exhaust flange at the cylinder head and the mounting nuts on the back of the mufflers. Slide the exhaust pipe and muffler assembly off the bike.
- Look carefully at the exhaust ports on the cylinder head. The old gasket is often buried under carbon and hard to see. Scratch the carbon off the surface with a small screwdriver — if you see copper, the old gasket is still in there.
- Gently pry the old copper gasket out with a small flathead screwdriver.
- Pop the new copper gasket into the exhaust port.
- Reinstall the exhaust pipe. When putting the exhaust collars back together, make sure the curved side faces the exhaust flange (away from the engine) — the thin side should face toward the engine and push the pipe into the gasket.
- Snug the 12mm nuts — do NOT over-tighten. The copper gaskets crush and conform to provide a seal. Over-tighten and you’ll flatten them too far, causing leaks all over again.
Our video covers exhaust gasket replacement as one of five often-missed maintenance jobs on vintage Hondas, including collar orientation and tightening tips.
Frequently Asked Questions
Will this fit my CB450 or CB500T?
No. The CB450 and CB500T have a larger exhaust port diameter and require a different copper gasket. We sell those separately — see our CB450 / CB500T Copper Exhaust Gaskets.
What’s the difference between the copper gasket and the graphite gasket?
They go in different locations. The copper gasket seals the joint between the cylinder head exhaust port and the exhaust pipe header. The graphite gasket seals the joint between the exhaust pipe and the muffler. Most bikes need both — copper at the head, graphite at the muffler. We sell graphite exhaust gaskets for the CB350 / CB360 separately.
Can I reuse these gaskets?
Yes — if you don’t over-tighten them. Copper crush gaskets can be reused three to four times when removed and reinstalled carefully. Once they’re flattened beyond their crush range, replace them.
How do I know if my exhaust gasket is bad?
A ticking or popping sound near the cylinder head at idle is the most common symptom. You may also see black carbon deposits around the exhaust port flange where exhaust gas is escaping past the gasket. If you hear ticking near the muffler instead, that’s the graphite gasket between the pipe and muffler — a different part.
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Last updated: March 2026
