Gasket Kit (Service) | Honda CL350 / SL350 / CB350

Gasket Kit (Service) for Honda CB350 / CL350 / SL350

Everything you need for tune-up work, points service, clutch jobs, and any service that goes beyond an oil change but stops short of a full rebuild. Eleven gaskets covering the alternator cover, points cover, side covers, intake manifolds, and cam covers — the covers that come on and off a 350 twin on a regular basis. The middle tier of our three CB350-family gasket kits: bigger than the Oil Change kit, smaller than the Overhaul.

Why You Need This

If you're doing more than cleaning the oil filter, you're disturbing more than six gaskets. Pulling the points cover for ignition timing? That's gasket G. Removing the carbs for cleaning or rebuild? Both intake manifold gaskets (H). Opening the left side to service the clutch or stator? Gasket I. Adjusting valves or servicing the cam chain? Top and bottom cam covers (J and K). These gaskets are single-use — the old ones rip, tear, or get patched with cardboard and silicone. Until now you either goo everything back together or buy the full overhaul kit for $50. This kit sits in between: enough gaskets to cover the routine service work, not so many that you're paying for top-end pieces you don't need.

The same letter scheme carries across all three CB350-family gasket kits — A through F for oil service, A through K for this kit, A through U for the full overhaul. Upgrade or downgrade between them as your job changes.

Specifications

No RTV silicone on aluminum crankcase surfaces. The paper gaskets in this kit are cut to Honda's specified dimensions and seal on their own. Silicone squeezes into oil passages and makes the next service miserable. If you want an assembly aid, a thin smear of grease on both sides of a side-cover gasket keeps it from sticking when it's time to come off again. For the rare joint that actually needs sealer, use Honda Bond 4 (or Motoseal / Threebond) — latex-acetone base, not RTV.

Model-Specific Notes

• CB350 and CL350 (all years): Fit the kit as-sold. Identical right-side architecture across the CB and CL variants.
• SL350 K0 (1969–1970): Fits as-sold. Same bottom-end casting as the CB/CL 350.
• SL350 K1 (1971) and SL350 K2 (1972–1973): The bottom end was recast to eliminate the electric starter — case shape and gasket profile differ. Select the SL350 Add-On Gaskets option above before checkout. The add-on supplies the correct-profile gaskets for the K1/K2 case.

What's in the Kit

Gaskets A through K. The chart below shows all three CB350-family kits side-by-side — #4018 (Oil Change, A–F), this kit (Service, A–K), and #4031 (Overhaul, A–U) — so you can see exactly which letters fall in which kit.

Installation

Difficulty: Intermediate. Clean surfaces and proper torque are the two things that separate a leak-free reassembly from the "small oil leak from the points cover" that shows up a month later.

Tools needed: JIS screwdriver set (or the CMC Allen bolt upgrade kit — see below), circlip pliers, 16 mm T-handle lock nut wrench (for oil filter lock nut if you go into the right side), torque wrench, clean rags, brake cleaner or acetone for surface prep, Honda Bond 4 (or Motoseal / Threebond) for the joints that need sealer.

1. Scrape every trace of old gasket material off both sides of each mating surface. Honda's service manual specifies a maximum warpage of 0.05 mm (0.002 in.) on gasket surfaces — if a cover is warped past that, lap it flat on a surface plate before you bolt it back on. No gasket in the world will seal a distorted surface.
2. Clean with brake cleaner or acetone. Old oil and silicone residue keeps new gaskets from seating properly.
3. Install gasket G (points cover): Install the ignition advance plate and points plate, route wires through the grommet, then install the points cover with a fresh gasket. Finger-tight, then snug with a short screwdriver — don't over-torque or you'll distort the thin cover.
4. Install gaskets H (intake manifolds): Two gaskets for the twin carburetors. Orient correctly against the head, slide the manifolds on, and torque the mounting bolts gradually in a cross pattern. Check for air leaks with carb cleaner after idle.
5. Install gasket I (left crankcase cover): Apply a light coat of grease to both sides of the gasket before installing — makes removal next time much easier. Route the stator wiring under the engine through the holding clamp, connect the neutral light bullet to the switch, and install the cover bolts with anti-seize on the threads.
6. Install gaskets J (top cam cover) and K (bottom cam cover): The cam box gasket (K) goes on first with the passage hole aligned to the front right side hole in the casting — if this hole doesn't line up, the cam chain tensioner will starve for oil. Install the metal baffle plate next, then the top cam cover gasket (J), then the top engine cover.
7. Final torque sequence: Work from center outward on every cover. Even pressure prevents the aluminum from warping under the bolt heads.

Rocker shaft O-rings (U) are NOT in this kit. If your valve cover leaks from around the rocker adjusters, those seals are in the Overhaul Kit (#4031), not here. A surface leak from the cam cover gasket itself is J or K — in this kit.

Our CB350 / CL350 Engine Rebuild Part 2 video covers clutch, oil pump, and cam chain tensioner install — including gaskets F, A, E, and I. Our Rebuild Part 5 covers the final points cover and cam cover gasket install (gaskets G, J, and K). The Complete Reassembly of the Honda CB350 / CL350 / SL350 Twin KB article is the step-by-step written companion to the whole video series.

Frequently Asked Questions

Which kit do I actually need: 4018 Oil Change, 4015 Service, or 4031 Overhaul?

If you're only cleaning the oil filter, 4018 is enough. If you're doing anything that involves the points cover, the carbs, the left side (clutch or stator), or the top cam covers, this kit (4015) covers you. If you're tearing the motor apart with the head and cylinder off for a full rebuild, go straight to 4031 — it adds the head gasket, cylinder base, exhaust gaskets, cam tensioner gasket, and rocker shaft O-rings on top of everything in 4015.

I have a 1971 SL350 K1. Does this kit fit?

Partially. The SL350 K1 and K2 have a slightly different bottom-end casting — Honda dropped the electric starter and recast the case, which changed the sealing profile for gasket F (right crankcase cover) and some adjacent joints. You need this kit plus the SL350 Add-On Gaskets option to seal correctly. Select the add-on above before checkout.

My points cover is leaking oil. Is this the right gasket?

Yes — gasket G is the points cover gasket, included in this kit. Oil working its way up to the points and fouling them is one of the most common leaks on a high-mileage 350. Replace the gasket, clean the seating surface thoroughly, and don't over-torque the cover bolts. If the leak persists after the gasket swap, check for a cracked or warped points cover itself.

Does gasket K include the rocker shaft O-rings?

No. Gasket K is the bottom cam cover gasket — the flat paper gasket that seals the cam cover casting to the head. The rocker shaft O-rings (at the outer end of each rocker arm) are a separate piece and are only included in the Overhaul Kit #4031 as gasket U. If your valve cover leaks from around the rocker adjusters, you need the rocker shaft O-rings (U), not gasket K.

Can I use silicone sealer with this kit?

No. The gaskets in this kit are cut to Honda's specified dimensions and seal on their own without any sealant on most joints. Silicone on an aluminum crankcase surface squeezes into oil passages and can starve the engine. For joints that need sealer (mostly the cam-box-to-head area), use Honda Bond 4 (or Motoseal / Threebond) — latex-acetone base. A light coat of grease on the paper gaskets helps them seat without sticking, and makes removal easier next time.

I already have an Overhaul Kit (#4031). Do I need this too?

No. The Overhaul Kit includes everything in this kit plus the top-end gaskets. If you already have 4031 and you're doing service work, use the A–K gaskets from your overhaul kit.

You Might Also Need

• Gasket Kit (Oil Change) #4018 — CB350 / CL350 / SL350 — downgrade if you just need the oil-service gaskets
• Gasket Kit (Overhaul) #4031 — CB350 / CL350 / SL350 — upgrade for a full engine rebuild
• Oil Seal Kit — CB350 / CL350 / SL350 — if you're opening cases, replace the oil seals while you're in there
• Ignition Contact Points Kit — CB350 / CB360 — most customers doing points service replace the points at the same time
• Ignition Condenser — CB350 / CB360 / CB450 — companion to the points kit
• Ignition Rebuild Kit — CB350 / CB360 / CB450 — full ignition refresh
• Clutch Rebuild Kit #K4052 — CB350 / CL350 / SL350 / CB360 / CL360 / CJ360 — if you're opening the left side for clutch work
• Intake Manifold — CB350 / CL350 / SL350 K0 — replace cracked manifolds while you're in there
• Intake Manifold — SL350 K1 / K2 — SL350 K1/K2 specific manifolds
• Allen Bolt Kit (Lower) #4030 — CB350 / CL350 / SL350 K0 — replaces the factory Phillips screws that cam out when you try to back them off
• Allen Bolt Kit (Lower) #4301 — SL350 K1 / K2 — SL350 K1/K2 specific Allen bolts
• Allen Bolt Kit (Upper) #4027 — CB350 / CL350 / SL350 — companion to the lower kit for the top-end bolts
• Zinc ZDDP Oil Additive — at the refill after any engine service
• Honda Bond 4 Gasket Sealer — for joints that genuinely need sealer (NOT for most covers in this kit)

Last updated: April 2026