Gasket Kit (Overhaul) | Honda CB450 / CL450 / CB500T

Honda CL450 / CB450 / CB500T Gasket Kit (Overhaul)

The whole motor is on the bench. Pistons are out, head's off, cylinders are pulled. This is the top tier of three CB450 family gasket kits — 23 gasket types (43 individual pieces) covering every paper gasket, O-ring, copper washer, and valve stem seal touched during a full top-to-bottom rebuild of the DOHC parallel twin.

Why You Need This

Choose this kit when the cylinder head and cylinders are coming off. Letters A–F carry over from Oil Change tier (routine right-side filter clean), G–J from Service tier (intake reseal, points cover, 4 valve adjuster covers, left crankcase cover), and K–W are the new-in-Overhaul gaskets — head gasket, cylinder base, cylinder base O-rings, alignment dowel seals, exhaust gaskets, valve guide base O-rings, valve stem seals, rocker shaft O-rings, camshaft end covers, cam tensioner gasket, top cam chain roller shaft O-ring, and dipstick O-ring.

The head gasket (Letter P), valve stem seals (Letter W, qty 4), cylinder base O-rings (Letter S), and valve guide base O-rings (Letter T, qty 4) are NOT sold individually except through this kit. This is the only way to source them as a complete set for a CB450 family overhaul.

Specifications

Note — the kit includes the 4 valve stem seals (Letter W). Customers regularly ask whether the Overhaul kit covers the valve stem seals or whether they need to order them separately — the answer is yes, the kit ships with 4 valve stem seals (one per valve, 2 intake + 2 exhaust). If you only need the valve stem seals as a standalone, see our CB450 / CL450 / CB500T Valve Stem Seals standalone product.

Note — head gasket, cylinder base, valve stem seals, valve guide base O-rings, and cylinder base O-rings are not sold individually. Letters P, K, W, T, and S only ship as part of this Overhaul kit. We bundle them with the other top-end gaskets that need replacement any time the cylinders come off.

Note — install gaskets dry; use Honda Bond 4 only on the cylinder head dowels. Do NOT use RTV silicone — it sheds debris into the oil galleries on these wet-clutch engines. Honda Bond 4 is the correct sealant for the crankcase mating surfaces and the cylinder head alignment dowels — never on the head gasket face itself. The head gasket installs dry between the cylinder and head.

Model-Specific Notes

• CB450 K0 "Black Bomber" (1965–1967) — gaskets fit identically across all K-suffix CB450 years. The K0's wiring is different from later models, but the gasket kit is the same.
• CL450 Scrambler = K0 (1967) through K6 (1974) only. Honda never produced a CL450 K7. CL450 K5 was sold across both 1972 and 1973 model years — either year is the K5.
• CB500T (1975–1976) is the bored-out evolution of the CB450 DOHC twin (498cc vs 444cc). Same gasket footprint, same kit.
• Does not fit CB500K or CB550K/F. Those are inline-four-cylinder bikes, entirely different engine family. "CB500" alone is ambiguous — check whether your bike is a CB500T (twin, this kit fits) or CB500K (four, this kit does NOT fit).
• Does not fit CB350 / CB360 / CB175 / CB200 / CB550K / CB550F / CB750. Each is a different engine architecture with different gasket sizes.

What's in the Kit

This Overhaul kit includes everything from the Service kit (Letters A–J) plus 13 more gaskets and O-rings (K–W) for full cylinder + head + valve work.

Installation

Difficulty: Advanced

Tools needed: JIS Phillips driver (or upgrade to Lower Allen Bolt Kit + Upper Allen Bolt Kit), torque wrench, single-edge razor blade, acetone, Honda Bond 4, anti-seize lubricant, valve spring compressor for valve stem seals (Letter W), piston ring compressor for cylinder reinstall, cam chain cutter/press (cam chain disconnect at the master link is required for head removal).

1. Drain oil. Remove engine from frame. Full overhaul on the CB450 family generally means engine out — remove fuel tank, disconnect starter cable and wiring, then lift engine onto a stand.
2. Strip the top end. Remove the carbs (disturbs Letter G intake manifold gaskets), points cover (H), both valve adjuster covers + 2 baffle gaskets (I — 4 total), camshaft end covers (L + M), cam chain tensioner cover (N), the cam chain (disconnect at the master link — cam chain replacement is normal Overhaul scope), the cylinder head (P), and the cylinders (K + S cylinder base O-rings + R alignment dowel seals).
3. If pulling the bottom end: remove both crankcase covers (D, E, F, J), drop the AC generator, filter rotor, transmission gears, kickstarter shaft, then split the cases. Honda Bond 4 (not RTV) seals the crankcase mating surfaces on reassembly.
4. Clean every mating surface. Use a razor blade and acetone. Scrape every trace of old paper, RTV, or sealing agent. Any residue under a fresh gasket is the most common cause of post-rebuild leaks.
5. Inspect the head + cylinder bores. A warped head won't seal regardless of how perfect the gasket is. The CB350 / CB360 / CB450 / CB550 Deck/Level Head Gasket Surfaces guide walks through the head-prep procedure. For machine work: our Cylinder Boring & Honing Service handles CB450/CL450 cylinder prep (CB500T not covered).
6. Valve work + Letter W valve stem seals. While the head is off, this is the moment for valve job, valve guide replacement (if needed — use the bronze valve guides and ream to size), then 4 fresh valve stem seals (Letter W). Use a valve spring compressor; oil each stem before seating the seal. Letter T (4 valve guide base O-rings) install along with the seals.
7. Cylinder reinstall. Place the 2 alignment dowels (Letter R) and 2 cylinder base O-rings (Letter S) in the upper crankcase. Lay the cylinder base gasket (Letter K) DRY. A small bead of Honda Bond 4 around the oil passages on the upper crankcase before laying the base gasket is acceptable for the dowel area only — do NOT use RTV.
8. Head install. Place 3 dowel pins on top of the cylinder, 2 new O-rings on the dowels (a dab of Honda Bond 4 on the dowels is fine), then the head gasket (Letter P) DRY. Lower the head over both cam chains threaded through the cam tunnel. Install copper washers under the head cap nuts — these aren't trim, they seal the oil flow through the hollow cylinder studs that feed the top end.
9. Torque the head cap nuts in stages, criss-cross pattern. Brenden walks the exact torque value + sequence in the install video below — copy it. Uneven loading is the most common cause of post-overhaul head leaks.
10. Cam chain + camshaft. Thread the cam chain over both cam sprockets (intake + exhaust — this is a DOHC engine). Align the cam timing marks with the LT mark on the crankshaft. Install the cam tensioner cover (Letter N gasket) and the cam chain master link with a chain press.
11. Camshaft end covers. Three Letter M gaskets + one Letter L gasket (behind points cover). Top cam chain roller shaft sealing O-ring is Letter Q.
12. Rocker shaft O-rings (Letter U, qty 4). Four O-rings on the rocker shafts — replace on reassembly.
13. Reseat ancillary covers. Right crankcase cover with Letter E gasket. Left crankcase cover with Letter J gasket (light coat of white lithium grease on both sides — lets the cover release cleanly at next service). Intake manifolds with Letter G gaskets. Points cover with Letter H. Stator rotor cover with Letter F + Letter A bolt O-rings (3). Oil rotor with Letter B. Oil rotor cover with Letter C (small) + Letter D (filter cover).
14. Refill engine oil. 2.8 L / 2.9 US qt of SAE 10W-40 100% mineral oil + 2 oz of Zinc ZDDP additive per quart. Avoid semi-synthetic — modern reformulated diesel oils (Shell Rotella T4, Chevron Delo 400, Mobil Delvac 1300, all reformulated to semi-synthetic in late 2023) cause clutch slip on CB450 wet clutches.
15. Set valve clearance + ignition timing. CMC recommends 0.08 mm (0.003 in) valve clearance — looser than Honda's factory 0.03 mm spec to prevent cam-lobe wear. Overshoot method: 0.004 in feeler, then back off. See the CB450 / CL450 / CB500T Valve Adjustment & Cam Chain KB for the full procedure.
16. Heat-cycle and retorque. After the first short ride (5–10 minutes warm), let cool, then retorque the head bolts. Check for weeps at head-to-cylinder, cylinder-to-case, and exhaust gasket joints.

Installation Tip: Thoroughly clean every gasket surface to remove any bits of old gasket material or silicone residue before installing fresh gaskets. A light coat of white lithium grease on the side cover gaskets (E, F, J) lets the cover release cleanly at next service. Honda Bond 4 only for the cylinder head dowels and crankcase split — never RTV.

Engine Rebuild Part 5 covers head install + cam chain alignment + master link press + side cover reassembly — the back half of the overhaul scope. The full 5-part series walks through teardown to final assembly: Pt 1 — Bottom End Assembly, Pt 2 — Top End Bottom-End Wrap-up, Pt 4 — Head Prep, and the video above (Pt 5).

Frequently Asked Questions

Does this Overhaul kit include the 4 valve stem seals?

Yes — Letter W is 4 valve stem seals (one per valve, 2 intake + 2 exhaust). They're sourced the same as our standalone CB450 / CL450 / CB500T Valve Stem Seals product. This is the most-asked question on this page — you don't need to order them separately if you're already ordering this kit.

What's the difference between #4019 Oil Change, #4064 Service, and #4035 Overhaul?

Three tiers, cumulative letter scope:

• #4019 Oil Change (A–F): Six gaskets and O-rings for routine oil and centrifugal filter clean.
• #4064 Service (A–J): A–F plus four more (G–J) — intake manifolds, points cover, 4 valve adjuster covers, left crankcase cover. Covers valve adjustment, ignition timing, and carb reseal.
• #4035 Overhaul (A–W): Everything in the Service kit plus 13 more gaskets and O-rings (K–W) for full cylinder + head + valve work — head gasket, cylinder base, valve stem seals, valve guide base O-rings, alignment dowel seals, cam chain tensioner gasket, camshaft end covers, rocker shaft O-rings, and more.

I bored my cylinders oversize — will the head gasket still fit?

Up to 71 mm bore (the standard cylinder is around 70 mm), the stock head gasket in this kit will still seal. Above 71 mm, you're past what the gasket bore can cover and you'd need a custom-cut gasket.

My CB450 is smoking out one exhaust — do I need this kit?

Smoking out the exhaust on a CB450 family engine is most often a valve stem seal failure (Letter W) — the rubber seal at the top of the valve guide cracks or hardens with age and lets oil down the valve stem into the combustion chamber. The fix requires pulling the head, which means you'll touch every gasket in this kit on the way back together. The Overhaul kit covers the full reassembly. The Service Kit (#4064) is not enough if the head is coming off.

Where do I use Honda Bond 4 in this rebuild?

Two specific places: (1) a thin bead on the cylinder head dowels (Letter R area) before the head gasket goes on, and (2) the crankcase split mating surfaces if you've split the bottom end. The head gasket (Letter P) and cylinder base gasket (Letter K) themselves install DRY — no sealer on the gasket faces. Do NOT use RTV silicone anywhere on this engine — it sheds debris into the oil galleries on the wet-clutch system.

Does this fit my CB500T?

Yes. The CB500T (1975–1976) is the bored-out evolution of the CB450 DOHC twin — same engine architecture, same gasket footprint. However, if you're also rebuilding pistons or having cylinders bored, those services are CB450/CL450 only:

• Our Forged Piston Kit and "Pulsar" Oversize Piston Kit fit CB450/CL450 ONLY — CB500T uses a unique piston design.
• Our Cylinder Boring & Honing Service does NOT cover CB500T — CB450/CL450 only.

Does this fit my CB500K or CB550K/F?

No. Those are inline-four-cylinder bikes — entirely different engine family. The "CB500" name is ambiguous: the CB500T is a DOHC parallel twin (this kit fits) and the CB500K is the four-cylinder predecessor of the CB550 (this kit does NOT fit).

Does this kit fit my CB450 K0 "Black Bomber"?

Yes. Gaskets fit identically across all CB450 K-suffix years (K0 through K7, 1965–1974). The K0 has different wiring from later models, but the gasket fitment is unchanged.

Should I upgrade the cover bolts to Allen bolts while I'm in there?

Yes — the original Phillips screws strip easily, especially after 50 years of impact-driver service. The Lower Allen Bolt Kit covers side covers + oil pump area. The Upper Allen Bolt Kit covers valve covers, points cover, cam end covers — most relevant for top-end work.

You Might Also Need

• #4019 Gasket Kit (Oil Change) CB450 / CL450 / CB500T — Letters A–F, smallest tier
• #4064 Gasket Kit (Service) CB450 / CL450 / CB500T — Letters A–J, middle tier
• CB450 / CL450 / CB500T Oil Seal Kit — engine shaft seals (different parts, no overlap with gasket kit) — mandatory companion during overhaul
• CB450 / CL450 / CB500T Cam Chain — fresh chain at overhaul time (cam chain disconnect is required for head removal)
• Cam Chain Roller CB450 — companion to cam chain replacement
• Camshaft Gear Rubber Cushion — cam chain damper, replace while accessible
• CB450 / CL450 / CB500T Valve Stem Seals (standalone) — Letter W spare path, set of 4
• CB450 / CL450 / CB500T Valve Guides — bronze guides, 4 per engine
• "Airlock" Intake & Exhaust Valves CB450 / CL450 / CB500T — replacement valves if needed during valve job
• Piston Rings CB450 / CL450 / CB500T — sold per piston, need 2 sets per engine
• Forged Piston Kit CB450 / CL450 — CB450/CL450 only (NOT CB500T)
• "Pulsar" Oversize Piston Kit CB450 / CL450 — 0.5mm or 1.0mm oversize, CB450/CL450 only
• Wrist Pin Kit CB450 / CL450 / CB500T
• Cylinder Boring & Honing Service — CB450/CL450 only (CB500T not covered)
• Allen Bolt Kit (Lower) CB450 / CL450 / CB500T
• Allen Bolt Kit (Upper) CB450 / CL450 / CB500T
• Ignition Contact Points Kit — replace during reassembly tune-up
• Ignition Rebuild Kit
• "Shockwave" Electronic Ignition System — modern points-replacement
• Carburetor Rebuild Kit CB450 / CL450 / CB500T — full carb refresh while the manifolds are off
• Carburetor Gasket & O-Ring Kit
• Carb Intake Manifold (rubber boot)
• OEM-Style Oil Drain Plug
• "Black Hole" Premium Oil Drain Plug
• Honda Bond 4 Gasket Sealer — cylinder head dowels + crankcase split
• Anti-Seize Lubricant — for cover bolt reinstall
• Zinc ZDDP Oil Additive — 2 oz per quart at first fill after rebuild

Last updated: May 2026