Honda Front Fork Bolt & Copper Washer | CB175 / CB200 / CB350 / CB360 / CB450 / CB500 / CB550 / CB750
During any front fork rebuild, one special Allen-head bolt and one copper sealing washer hold each fork leg together. The bolt lives in a recess at the bottom of the fork leg, above the front axle holder. It's notorious for stripping out when stuck — and the moment you see a rounded-off head, you need a replacement ready. This kit is one fresh OEM-spec bolt and one annealed copper washer.
Why You Need This
The bottom socket bolt is what clamps the fork pipe to the fork bottom case. Every fork seal swap, every fork oil change, every stanchion-tube replacement on the CB175 K7 through the CB750 family requires removing this bolt. The original bolts have a unique Allen-head shape that doesn't always index cleanly on modern sockets, and they tend to get stuck in the fork leg after decades of heat, vibration, and slightly-off threadlock. The moment someone tries to break one free with an L-shaped Allen wrench, the head rounds off.
Swapping a stripped bolt with a random hardware-store M6 Allen works in a pinch, but it doesn't seat the copper sealing washer the way the factory design calls for. Oil seeps past the bottom joint on every ride. This kit is the correct bolt and a fresh, annealed copper washer — sold as a set because you need both.
What's in the Kit
- One Allen-head fork bolt (OEM-spec, correct head profile for Honda's fork tool)
- One copper sealing washer (annealed, unused)
Specifications
| Spec | Detail |
|---|
| Replaces OEM Part Numbers | 90116-383-721, 90116-283-010, 90544-283-000 |
| Fits Models | CB175 K7 / CL175 K7 (1973), CB200 / CL200 (1973–1976), CB350 K4–K5 / CL350 K4–K5 (1972–1973), CB350G (1973), CB360G / CB360T (1974–1976), CL360 K0–K1 (1974–1975), CJ360T (1976–1977), CB450 K5–K7 (1972–1974), CL450 K5–K6 (1972–1974), CB500T (1975–1976), CB500K (1971–1973), CB550K (1974–1978), CB550F (1975–1977), CB750 K2 (Frame SN 2093731 forward), CB750 K3–K8 (1973–1978), CB750F, CB750A |
| Kit Contents | 1 Allen-head fork bolt + 1 copper sealing washer |
| Sold As | One kit per order — order two per bike (you have two fork legs) |
Order two per bike. Each fork leg has its own bolt-and-washer. Doing a full fork rebuild on both legs means ordering two of these kits.
CB750 K2 mid-production change. The CB750 K2 fork architecture changed partway through production. This bolt fits K2 bikes with frame serial number 2093731 forward. Earlier K2 bikes used a different fork design with a different bottom bolt.
Does NOT fit the early external-spring forks. CB175 / CL175 K0–K6 (1968–1972), early CB350 / CL350 K0–K3 (1968–1971), and CB450 / CL450 K0–K4 (1965–1971) all use external-spring fork architecture with a different bottom hardware setup. Pre-1971 CB350 owners can often source a substitute bolt from a hardware store. Also does NOT fit CT90 / Trail 90 (completely different fork architecture), or CB350F / CB400F (four-cylinder bikes with different fork hardware).
Model-Specific Notes
- Sealed-spring forks (CB175 K7, CL175 K7, CB200, CL200): short fork legs, this kit's bolt is the same diameter but the fork pipes themselves are shorter.
- Internal-spring without dampening rod (CB350 K4–K5, CL350 K4–K5, CB350G, CB360, CL360, CJ360, CB550K, CB550F): standard architecture. Follow the disassembly procedure below.
- Internal-spring with dampening rod (CB450 K5–K7, CL450 K5–K6, CB500K, CB500T, CB750 K2+): same bolt, but the dampening rod inside the fork pipe will try to spin when you break the bolt free. Compress the fork (sit on the bike or ratchet-strap the front down) before applying wrench force — pressure on the spring pins the dampening rod so it won't rotate.
Installation
Difficulty: Intermediate — the first one always fights you.
Tools needed: M6 Allen socket bit on a 3/8" drive ratchet or breaker bar (not an L-shaped Allen wrench — those round the head out), heat gun, drain pan, Honda Bond 4 or equivalent thread sealant for reassembly.
Removal (per fork leg):
- Drain the fork oil first. Remove the drain plug at the bottom of the fork leg and let the oil fully pour out — actuate the fork a few times to empty it.
- Apply heat from a heat gun to the fork bottom case around the bolt for 10–15 minutes. Old thread sealant needs to loosen up before the bolt will break free.
- Compress the fork — sit on the bike, or use a ratchet strap from the handlebar down to the front wheel. The compressed fork spring keeps the dampening rod (if equipped) from spinning inside the fork pipe when you crack the bolt loose.
- With the fork under compression, use the Allen socket on a breaker bar to break the bolt free. Lean on it steadily. Rounded-head panic is what happens when you yank sideways.
- Remove the bolt and the copper washer. Check that the washer didn't stick inside the fork body — it often does. Fish it out with a magnet or a pick.
Reassembly:
- Apply a thin coat of Honda Bond 4 (or equivalent anaerobic thread sealant) to the new bolt's threads. This is what keeps the bottom joint from leaking fork oil.
- Install the new copper washer on the bolt.
- Thread the bolt into the fork bottom case by hand first, then snug it up with the Allen socket. Honda doesn't publish a specific ft-lb value for this bolt — "tight enough to not leak, not so tight you strip it again" is the rule. If it's holding fork oil and not weeping, you're done.
- Refill with fresh fork oil to your model's specified capacity (see Installation Tip below).
Fork oil capacity per leg (from our fork-rebuild KB articles):
- CB350 K4–K5 / CL350 K4–K5: 135–140 cc
- CB360 / CL360 / CJ360: 135–140 cc
- CB450 K5 / CL450 K5–K6: 160 cc
- CB450 K6–K7: 140 cc
- CB500T: 140 cc
- CB500K: 160–170 cc
- CB550K / CB550F: 165–190 cc
Our How To Identify Fork Architectures video walks through the four different fork designs on vintage Honda twins and fours so you know which rebuild procedure applies to your bike. We also have dedicated rebuild videos for each architecture on the Common Motor YouTube channel.
Frequently Asked Questions
How many of these do I need?
Two per bike. Each fork leg has its own bolt-and-washer at the bottom. If you're doing a full fork rebuild on both legs, order two kits.
Does this fit my early CB175 (K0–K6) or early CB350 (K0–K3)?
No. Those bikes use an external-spring fork architecture with different bottom hardware. Pre-1971 CB350 / CL350 bolts are usually close enough to a standard hardware-store M6 Allen that customers can source a substitute locally. CB175 K7 (1973 only) is the one CB175 year that uses our bolt.
My bolt head is already stripped — how do I get it out?
Two common approaches: (1) heat the fork bottom with a heat gun, then hammer a slightly-oversized Torx bit or a collapsed Allen socket into the rounded head until it grips; (2) drill the head off with a 21/64" bit until the bolt head separates from the shank, remove the fork pipe, then pull the remaining shank out with vise grips. Either way, plan on replacing the bolt — that's what this kit is for.
Can I reuse the old copper washer?
No. Copper washers work-harden after being compressed once and won't re-seal properly the second time — you'll get fork oil seeping from the bottom joint. This kit includes a fresh annealed washer for exactly that reason.
What thread sealant should I use?
Our Honda Bond 4 is what we use in the shop. It's the same product Honda's factory service manuals call "locking sealant" in the fork-reassembly steps. Any anaerobic thread sealant (e.g., Yama-Bond, Three Bond 1104) works. Do not use plain Loctite — the bolt needs to be removable for the next fork service.
Does this fit my CT90 / Trail 90?
No. The CT90 uses a fundamentally different fork architecture — the fork and fork cushions come out together as a unit. The CT90 does not have this bottom socket bolt.
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Last updated: April 2026
