Copper Exhaust Pipe Gaskets | Honda CB450 / CL450 / CB500T
Tick, tick, tick — hear that ticking 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 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. Over time they crush flat and disappear under carbon buildup — most people don't even know they're there until the ticking starts. An exhaust leak at the port throws off your air/fuel mixture and makes tuning frustrating. And every time the pipes come off during restoration work, the gaskets take a hit.
These copper replacements crush and conform as you tighten the exhaust joint, forming a tight seal against the cylinder head port. The CB450, CL450, and CB500T all use this gasket — a different size than the one for the CB350 / CB360 twins.
Specifications
| Spec | Detail |
|---|
| OEM Part Numbers | 18291-MM8-880, 18291-283-010, 18291-283-306 |
| Fits Models | CB450 K0–K7 (1965–1974), CL450 K0–K6 (1967–1974), CB500T (1975–1976) |
| Material | Copper |
| Sold As | Pair (two gaskets — one per cylinder) |
Note: Sold as a pair — you need two per bike, one for each exhaust port. Grab a few extras while you're ordering; you'll use them.
Note: The CB350 and CB360 twins use a smaller-port copper gasket — see our CB350 / CB360 Copper Exhaust Gaskets. Do not use this CB450 / CB500T gasket on a 350 or 360.
Installation
Difficulty: Beginner
Tools needed: Wrench for the exhaust pipe joint nut, small flathead screwdriver
- Unbolt the exhaust pipe joint at the cylinder head and the muffler mounts, then slide the pipe-and-muffler assembly off the bike.
- Look closely at the exhaust ports. The old gasket is usually buried under carbon — scratch the surface with a small screwdriver, and if you see copper, the old gasket is still in there.
- Gently pry the old copper gasket out with the flathead screwdriver.
- Drop the new copper gasket into the exhaust port.
- Loose-fit the exhaust pipe and joint at the head first — get the joint started but don't tighten it yet. Bolt up the muffler, then fully tighten the pipe joint. (Tighten the joint first and you'll fight the muffler going on.)
- Snug the joint just enough to seat the gasket — the copper crushes and conforms to form the seal. Don't over-tighten, or you'll flatten it too far and start the leak all over again.
Our video covers exhaust gasket replacement as one of five often-missed maintenance jobs on vintage Hondas, including how to find the old gasket and snug it down without crushing it flat.
Frequently Asked Questions
Will this fit my CB350 or CB360?
No. The CB350 and CB360 twins have a smaller exhaust port and use a different copper gasket. We sell those separately — see our CB350 / CB360 Copper Exhaust Gaskets. This gasket is for the CB450, CL450, and CB500T.
What's the difference between the copper gasket and the graphite gasket?
They seal different joints. The copper gasket seals the joint between the cylinder head exhaust port and the exhaust pipe. 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. For the CB450 / CB500T, the matching graphite gasket is our Graphite Exhaust Gaskets — CB450 / CB500T.
My replacement mufflers still leak at the pipe — what now?
Aftermarket mufflers don't always seal tightly at the pipe joint. The fix is an aluminum shim around the pipe plus a T-bolt clamp to pull the joint tight — we walk through it in our guide to stopping replacement-muffler leaks on the CB450 / CB500T.
How do I know if my exhaust gasket is bad?
A ticking or popping sound near the cylinder head at idle is the classic symptom. You may also see black carbon deposits around the exhaust port flange where gas is escaping past the gasket. If the ticking is back near the muffler instead, that's the graphite gasket between the pipe and muffler — a different part.
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Last updated: June 2026
