Gaskets Overhaul Kit | Honda CB350 / CL350 / SL350
If you've decided to tear the engine all the way down, you need every gasket and O-ring to put it back together right. This 21-piece overhaul kit covers the complete CB350 / CL350 / SL350 twin from crankcase to cam box — every paper gasket, rubber O-ring, and exhaust gasket required for a full engine and transmission rebuild. Made in Japan.
Why You Need This
A full engine overhaul means splitting the cases, pulling the top end, and replacing every sealing surface in the motor. Reusing old gaskets — or worse, trying to seal things with silicone — leads to oil leaks, blown head gaskets, and repeat teardowns. The 350 twin is especially prone to oil seepage around the head gasket oil passages, where Honda skipped the O-ring or dowel pin that later models like the CB360 and CB450 received. Fresh gaskets with proper surface prep eliminate these leaks.
We build these kits ourselves and source the gaskets from Japan. This is the most complete and accurate overhaul gasket kit on the market for the Honda 350 twin.
Specifications
| Spec | Detail |
|---|
| Replaces OEM Part Numbers | 91301-426-010, 91301-393-000, 91309-286-000, 91355-415-000, 15291-286-300, 11691-286-306, 11691-286-000, 11394-286-306, 11394-286-040, 11394-286-030, 30372-286-306, 30372-286-320, 16229-369-306, 16229-286-000, 16229-369-000, 11395-312-306, 11691-354-306, 11691-216-000, 11394-340-000, 11394-312-020, 12261-286-306, 12261-286-020, 12261-286-030 |
| Fits Models | CB350 K0–K5 (1968–1973), CL350 K0–K5 (1968–1973), SL350 K0–K2 (1969–1973) |
| Kit Contains | 21 pieces — paper gaskets, rubber O-rings, exhaust gaskets |
| Origin | Made in Japan |
| Sold As | Complete kit |
Note: SL350 K1 and K2 engines use a few different gaskets from the CB, CL, and SL350 K0 engine — the castings are different shapes. Check the box for the optional add-on part and we will modify the kit for the SL350 K1/K2.
What's in the Kit
This overhaul kit includes gaskets A through U. It contains everything in both the Oil Change Kit (#4018, gaskets A–F) and the Service Kit (#4015, gaskets A–K), plus all the top-end and head gaskets needed for a complete engine overhaul.
Installation
Difficulty: Advanced — full engine teardown and reassembly
- Clean all gasket surfaces thoroughly and remove every trace of old gasket material and silicone. Inspect each surface for warping — Honda specifies a maximum of 0.05 mm (0.002 in.) distortion on gasket surfaces. If warped beyond that, deck the surface flat on a surface plate.
- Install the cylinder base gasket and two guide pins before dropping the cylinder onto the pistons.
- For the head gasket, check that the alignment dowel holes allow the gasket to sit flat. If the gasket bows slightly, file the dowel holes with a small round file until it seats flush.
- Apply a thin coat of copper spray gasket sealer to both sides of the head gasket — two light coats. Apply Honda Bond (or equivalent non-silicone sealant) around the oil passage holes on both the cylinder deck and head surfaces. On the 350 twin, these oil passages are the most common source of head gasket oil leaks.
- Set the head onto the cylinder, install the two 6 mm head-to-cylinder bolts, and torque to 85–100 kg-cm (6.1–7.2 lb-ft).
- A light coat of grease on gaskets like the side covers and cam end covers keeps them from sticking and tearing during future service.
The cam box gasket (S) and cam end cover gaskets (R) seal the valve spring wells, which fill with oil during operation. Apply gasket sealant to these surfaces to prevent oil seepage.
Our CB350 / CL350 Engine Rebuild Part 4 video covers the complete cylinder head and cam box gasket installation, including head gasket sealing techniques, cam shaft end play measurement, and rocker arm assembly. The full multi-part rebuild series walks through every step of the overhaul.
Frequently Asked Questions
What is the difference between the Oil Change, Service, and Overhaul kits?
They are nested. The Oil Change Kit (#4018) covers gaskets A–F — the right side cover, stator cover, and oil system gaskets you replace during a routine oil change. The Service Kit (#4015) adds gaskets G–K — points cover, intake manifolds, left crankcase cover, and cam covers. The Overhaul Kit (#4031) includes everything from both kits plus gaskets L–U — cylinder base, head gasket, exhaust gaskets, valve cover O-rings, cam tensioner, and all the top-end seals needed for a complete engine rebuild.
Does this kit fit the SL350 K1 or K2?
The SL350 K1 and K2 use slightly different engine castings from the CB350, CL350, and SL350 K0, which means a few gaskets are different shapes. Select the optional add-on when ordering and we will modify the kit to fit the SL350 K1/K2 engine.
Do I need to use gasket sealer with this kit?
For most gaskets, no — clean, flat surfaces and properly torqued fasteners are sufficient. The head gasket is the exception: apply copper spray gasket sealer and use Honda Bond (or a latex acetone-based sealer) around the oil passage holes. Avoid RTV silicone on aluminum crankcase surfaces. A light coat of grease on side cover gaskets makes future removal easier without tearing the gasket.
Should I replace oil seals at the same time?
Yes. If you have the engine completely apart for an overhaul, it makes sense to replace all the oil seals while everything is accessible. Our Oil Seal Kit covers the complete set for the CB350 / CL350 / SL350.
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Last updated: March 2026
