Gasket Kit (Oil Change) | Honda CB350 / CL350 / SL350

Gasket Kit (Oil Change) for Honda CB350 / CL350 / SL350

Every time you service the oil filter on a Honda 350 you disturb a handful of gaskets and O-rings that should never be reused. This is the minimum set — six pieces — to put the right side of the motor back together correctly after an oil filter clean or an oil pump inspection. Cheaper than an overhaul kit when that's all you need, and cheaper than trying to buy gasket E by itself (you can't — the stator-cover gasket is only sold inside this kit or larger).

Why You Need This

The CB350 and CL350 share a centrifugal oil filter built into the right crankcase cover. Unlike a modern cartridge filter, it's cleaned, not replaced — the rotor cap is meant to come off every other oil change (roughly every 3,000 miles). Opening the filter means disturbing gaskets B, C, and possibly A. Pulling the whole right crankcase cover for an oil pump inspection or deeper clean means disturbing A, E, F — and every bolt O-ring around the stator rotor cover.

The gaskets and O-rings in this kit are single-use. Rubber O-rings compress and harden once seated; old paper gaskets tear when you pry the cover off. Reusing them is the #1 cause of post-service oil leaks on these engines. Six pieces, twenty dollars, right the first time.

This is also the cheapest path to gaskets E and F individually — the Honda stator-cover gasket and right-crankcase-cover gasket are not sold separately in our catalog. If you only need one of those, this kit is still the answer.

What's in the Kit

This Oil Change Gasket Kit contains gaskets A through F. The chart below shows all three CB350-family gasket kits side-by-side: #4018 (this kit, oil-service scope), #4015 Service (adds gaskets G–K for points + cam covers + intake), and #4031 Overhaul (adds gaskets L–U for the top end and engine rebuild). If you upgrade later, the letter scheme continues from where you started.

Specifications

Gasket E is the reason to buy the whole kit. Customers routinely ask if they can purchase just the stator-cover gasket by itself. They can't — Honda's original part isn't stocked individually in our catalog. This kit is the cheapest path to gasket E, and the cheapest path to gasket F. If you only need one of those gaskets, you'll get the rest as spares.

Model-Specific Notes

• CB350 K0 (very early 1968 production): The earliest CB350 K0 used a simpler gasket without an O-ring groove on the filter cover. If your cover doesn't have any O-ring grooves cast into it, the plain-paper style came stock — the kit's O-rings still install correctly on a standard cover; an early-pattern cover uses only the paper gasket component.
• CL350 (all years): Fits the same as the CB350. No variation between CB and CL on the right-side cover.
• SL350 K0 (1969–1970): Fits this kit as-sold. Same right-side architecture as CB350 K1/K2 of the same era.
• SL350 K1 (1971) and SL350 K2 (1972–1973): The bottom end was recast to eliminate the electric starter. The right crankcase cover profile differs from the earlier bikes — gasket F alone won't seal correctly. If you have a 1971–1973 SL350, select the SL350 Add-On Gaskets option above before checkout. The add-on supplies the correct-profile gaskets for the K1/K2 case.

Installation

Difficulty: Beginner (filter clean with gaskets B and C only). Intermediate if you pull the full right crankcase cover to service the oil pump.

Tools needed: JIS screwdriver set (or the CMC Allen bolt upgrade kit — see below), drain pan, circlip pliers, 16 mm T-handle lock nut wrench (for oil filter lock nut), torque wrench, clean rags, degreaser.

1. Drain the oil. Warm the engine to circulate the oil, then pull the drain plug over a drain pan. Replace the sealing washer on the drain plug — these are single-use.
2. Remove the right crankcase cover (only if you're servicing the oil pump or inspecting deeper). Phillips-head bolts hold it on from the factory; these usually cam out once in fifty years. The Allen bolt upgrade kit (#4030 lower) is the fix. Bag and label the bolts as they come out — lengths vary by position.
3. Remove the oil filter cover. This is the smaller round cover bolted to the right side of the right crankcase cover. Three bolts. On CB350 and CL350 you can clean the filter without removing the larger cover — this is where gaskets B and C come in.
4. Open the filter rotor. Pull the internal circlip, lift the filter cap, straighten the tongue of the spring washer pawls, and remove the 16 mm lock nut with the T-handle wrench. Pull the rotor out.
5. Clean everything. Wipe out the accumulated sludge from inside the filter rotor and the cavity. Degreaser + clean rag. A centrifugal filter relies on the rotor throwing heavy particles to the outside — if it's caked, it isn't filtering.
6. Inspect the mating surfaces. Before reassembling the crankcase cover, inspect the crankcase and oil filter covers for cracks and damages to the mating surface since they will cause leaks. Scrape off every trace of old gasket material. No silicone — our kit's gaskets seal without it. If the surface is damaged, the gasket won't save it.
7. Reassemble the filter. Install the rotor cap, new oil filter rotor lock washer (always replace this — it's a single-use tab washer), torque the 16 mm lock nut, then bend the tab over to lock the nut. Check the oil pump lock washer too — replace with a new item if the cover came off. Critical: if you removed the oil pump rod, install it the correct way around; reversed, the pump won't work.
8. Install gasket B (oil rotor O-ring) and gasket C (two oil filter cover O-rings, same size). Light grease on the rubber before you seat them helps removal next time without destroying them.
9. Replace the oil filter cover. Torque the three bolts gradually in a cross pattern.
10. If you removed the right crankcase cover: clean the gasket face, install gasket F (right crankcase cover), gasket E (stator rotor cover), and the three A O-rings at the stator cover bolts. Torque the cover bolts gradually, working outward from the center.
11. Refill the oil. CB350/CL350 takes 2.1 US quarts; SL350 takes 2.3 US quarts. Use mineral 15W-40 diesel truck oil — and add 2 oz of zinc (ZDDP) additive per quart. Run for a few minutes, check for leaks, shut off, recheck oil level in the morning.

Surface prep, repeated: no silicone. This is the single most common mistake on these engines. The paper gaskets in this kit have enough compression to seal on their own. Silicone ooze adds nothing and makes the next service harder — you'll spend the first twenty minutes scraping it off.

Our oil filter clean video walks through gaskets B, C, E, and F on a 1969 CB350 — Brenden covers the filter rotor removal, clean, and reassembly plus the right-cover R&R. For the oil drain and refill steps, see our companion CB350 / CL350 / SL350 engine oil change video.

Frequently Asked Questions

Do I need to replace every gasket in this kit at every oil change?

No. Gaskets B and C (oil rotor O-ring and oil filter cover O-rings) get disturbed on every filter rotor clean — Honda calls for that every other oil change, so roughly once every 3,000 miles. Gaskets A, E, and F only come into play when you pull the full right crankcase cover — oil pump inspection, clutch service, or a deeper investigation. Gasket D (oil pump gasket) is only touched if you remove the pump itself. One kit will cover multiple services because not every gasket gets used every time.

Can I buy just the stator rotor cover gasket (E) or just the right crankcase cover gasket (F)?

Not from us. These Honda gaskets aren't stocked individually in our catalog — they're only sold as part of a kit. If you only need one of them, this is the cheapest way to get it. The spares go in your toolbox for the next service.

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

If you're cleaning the oil filter or looking at the oil pump, 4018 (this kit) has everything you need. If you're also doing ignition points service or pulling the left cover, step up to 4015 (adds the left crankcase cover, points cover, cam covers, intake gaskets). If you're tearing the motor apart for a full rebuild with the head and cylinder off, go straight to 4031 (adds head gasket, cylinder base, exhaust gaskets, valve cover O-rings, rocker shaft O-rings).

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

Partially. The SL350 K1 and K2 (1971–1973) have a slightly different bottom-end casting — Honda dropped the electric starter and recast the case, which changed the profile of the right-crankcase-cover sealing area. You need this kit plus the SL350 Add-On Gaskets option to seal correctly. Select the add-on option above before checkout and you'll get the right gaskets for the K1/K2 case.

Can I use silicone instead of these gaskets?

No. The gaskets in this kit are cut to match Honda's specified dimensions and will seal on their own without any sealant. Silicone on top of a new gasket creates unpredictable clearance, squeezes out into oil passages, and makes the next service miserable. If you want a light assembly aid to keep the paper gasket in place while you bolt the cover up, a thin smear of grease is the right tool — nothing else.

My oil leaked after reassembly. What did I do wrong?

Three common causes, in order of frequency: (1) old gasket material left on the mating surface — scrape every trace off both the cover and the case; (2) over-torqued bolts distorted the aluminum cover — a gradual crossing pattern at moderate torque is the fix; (3) the gasket itself was pinched or trapped during installation. If the leak persists after reseating with fresh gaskets on a clean surface, inspect the mating surface for cracks or machining damage — this is a known leak cause that gaskets can't fix.

You Might Also Need

• Gasket Kit (Service) #4015 — CB350 / CL350 / SL350 — upgrade for tune-up work (adds points, cam covers, intake)
• Gasket Kit (Overhaul) #4031 — CB350 / CL350 / SL350 — upgrade for full engine rebuild
• Allen Bolt Kit (Lower) #4030 — CB350 / CL350 / SL350 K0 — replaces factory Phillips screws that cam out; we show this on camera
• 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
• "The Black Hole" Oil Drain Plug — CB350 / CL350 / SL350 — replaces the factory drain plug; neodymium magnet catches wear particles
• OEM-Style Oil Drain Plug — CB350 / CB450 — standard replacement plug
• Oil Drain Plug Crush Washers — single-use; replace at every oil change
• Oil Seal Kit — CB350 / CL350 / SL350 — complementary seals for deeper work
• Zinc ZDDP Oil Additive — protects cam and rocker wear at every oil change
• Honda Bond 4 Gasket Sealer — for the rare joint that needs sealant (NOT for the covers in this kit)

Last updated: April 2026