Graphite Exhaust Gasket | Honda CJ360 / CB450 / CB500T
The graphite gasket between your exhaust pipe and muffler fails quietly. Once it goes, you'll hear popping or ticking near the joint, see black carbon around the seam, and find your carburetors harder to tune. This is the larger graphite gasket — the one for the CB450, CB500T, and the CJ360 2-into-1 headers. Not to be confused with the smaller graphite gasket used on the CB350 / CB360 / CL450.
Why You Need This
Exhaust gas escaping before the muffler costs you back pressure. On these bikes, the graphite gasket sits between the exhaust pipe and the muffler inlet (or, on the CJ360, between each header and the 2-into-1 collector). When the gasket compresses and breaks down over the decades, the joint stops sealing. The bike gets louder, the carbs get harder to tune, and black carbon builds up around the seam.
Don't confuse this with the copper head-to-pipe gasket. That's a different product and a different joint on the bike. Copper seals head to pipe; graphite seals pipe to muffler. Many Honda exhaust-leak complaints come from confusing the two.
Specifications
| Spec | Detail |
|---|
| Replaces OEM Part Numbers | 18392-MK5-000, 18391-292-300 |
| Fits Models | CJ360T (1976–1977), CB450 K0–K7 (1965–1974), CB500T (1975–1976) |
| Sold As | Individual gasket — order two per bike for the standard twin exhaust |
| Material | Graphite |
| Location | Pipe-to-muffler joint (not head-to-pipe) |
Factory exhaust only. This gasket is dimensioned for the factory CB450 / CB500T / CJ360 pipe-and-muffler combination. Aftermarket mufflers may fit IF the muffler inner diameter matches the gasket outer diameter — check your dimensions before ordering. If you're running our CB450 / CB500T replacement mufflers and the joint still leaks, see our KB article on sealing aftermarket mufflers for the aluminum-shim and T-bolt-clamp fix.
Model-Specific Notes
- CJ360T: These gaskets seal the two headers where they enter the 2-into-1 collector. The 2-into-1-to-muffler joint at the rear uses a different, smaller gasket (Honda OEM 18391-390-000) that CMC does not currently stock.
- CL450: Does NOT fit. The CL450 uses the smaller graphite gasket — see our CB350 / CB360 / CL450 graphite gasket instead.
- CB450 K0 (1965–1967): Verify your OEM part number matches 18392-MK5-000 or 18391-292-300 before ordering; early K0 models had production variations.
Installation
Difficulty: Beginner
Tools needed: 12 mm wrench or socket for the exhaust flange nuts and muffler mounting nuts, wire brush or small flathead screwdriver for cleaning the mating surfaces.
- Unscrew the exhaust pipe joint nuts at the cylinder head and the muffler mounting nuts at the rear bracket. Back off the exhaust clamp bolts where the pipe meets the muffler.
- Slide the muffler off the pipe end. The old graphite gasket is typically stuck to the pipe or buried inside the muffler inlet — pry it free with a small screwdriver.
- Clean both mating surfaces. Carbon and old gasket residue come off the pipe end and the muffler inlet with a wire brush. A clean surface is what makes the new gasket seal.
- Slide the new graphite gasket over the end of the exhaust pipe.
- Reassemble: slide the muffler back over the pipe and gasket. Tighten the clamp bolts evenly, then reinstall the muffler mounting nuts at the frame and the exhaust pipe joint nuts at the head. Snug, don't over-tighten — the gasket needs to compress but not blow out.
Our 5 Small Maintenance Jobs Often Missed video covers exhaust gasket replacement as one of five commonly-skipped maintenance items. Demo is on a CB-class twin, but the pipe-removal approach is the same on the CB450, CB500T, and CJ360.
Frequently Asked Questions
What's the difference between graphite and copper exhaust gaskets?
Copper seals the cylinder-head-to-exhaust-pipe joint. Graphite seals the pipe-to-muffler joint. Different locations, different sizes, different materials. They are not interchangeable — running a copper gasket where a graphite one belongs (or vice versa) will leak. Most of the “my new gasket still leaks” customer questions we get come from someone using the wrong gasket type.
How many do I need?
Two per bike for the standard twin exhaust on the CB450, CB500T, and CJ360. Sold individually so you can order what you need.
Will this work with my aftermarket mufflers?
Only if the inner diameter of your aftermarket muffler matches the outer diameter of the gasket. If you're running our CB450 / CB500T replacement mufflers and the joint won't seal, we have a KB article with the aluminum-shim workaround and we sell a universal T-bolt muffler clamp that grips tighter than the stock-style clamp.
Does this fit the CL450?
No. The CL450 uses a smaller graphite gasket — use our CB350 / CB360 / CL450 graphite gasket instead. The CL-series pipe-to-muffler diameter is different from the CB450.
What about the rear gasket on my CJ360 2-into-1?
That's a different part — Honda OEM 18391-390-000 — and CMC does not currently stock it. This gasket is for the two headers entering the 2-into-1 collector, not the collector-to-muffler joint at the rear.
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Last updated: April 2026
