Honda-SOHC

SOHC.co.uk Forums => SOHC Singles & Twins => Topic started by: Craizeehair on July 04, 2026, 08:25:07 AM

Title: CB350K2 Valve Stem Seals
Post by: Craizeehair on July 04, 2026, 08:25:07 AM

I am starting to address the cylinder head and have found that the engine gasket set that I ordered does not contain valve stem seals, I’m pretty sure that a previous kit I used on my CB360 came with them but couldn’t say for sure?

No problem I thought and I started to look to see where I can buy these but I can’t seem to find them shown on the parts manual, I have also checked on CMSL but again can’t seem to find them there?

Does anyone know if they actually came with valve stem seals, this engine has them but could someone have fitted them whilst carrying work previously?

Attached are photos of the valve stem seals on this cylinder head and the parts diagrams where I would have expected to find them, any help would be greatly appreciated?

(https://uploads.tapatalk-cdn.com/20260704/8aed2f16c64ca76ed4b2f3cc6111aa10.jpg)


(https://uploads.tapatalk-cdn.com/20260704/897c22e934da171b63a461808bf985d1.jpg)
(https://uploads.tapatalk-cdn.com/20260704/932e26d9aae6ee54b975fa4f513e5299.jpg)

Title: Re: CB350K2 Valve Stem Seals
Post by: Ken4004 on July 04, 2026, 11:32:32 AM

The gasket set I bought for my 400 F did come with valve stem seals so it was a complete kit so nothing extra to buy, sorry but I can’t remember where I bought it from might have been David Silvers.
I might have some old receipts in the shed .

Title: Re: CB350K2 Valve Stem Seals
Post by: Ken4004 on July 04, 2026, 11:46:19 AM

I found some valve stem seals on eBay see attached

Title: Re: CB350K2 Valve Stem Seals
Post by: Craizeehair on July 04, 2026, 12:45:33 PM

Thanks for that.

I’ve done some more digging and have read that the 350K engines didn’t have valve stem seals, that would seem feasible given that I can’t find them on the parts diagram but it seems some people do fit them and some don’t, there are some on mine but I don’t now know whether to fit them again or not?

Title: Re: CB350K2 Valve Stem Seals
Post by: McCabe-Thiele (Ted) on July 04, 2026, 01:29:26 PM

Valve stem seals on the inlet valves help reduce oil consumption, the vacuum on the inlet stroke tends to suck oil in past the guides, this can lead to excessive carbon build up on the valve.

I'm a fan of valve seals 👍

Title: Re: CB350K2 Valve Stem Seals
Post by: Craizeehair on July 04, 2026, 01:50:42 PM

Thanks Ted, I wasn’t sure if it was a must or must not do type of thing. That puts my mind at rest.

Title: Re: CB350K2 Valve Stem Seals
Post by: Bryanj on July 04, 2026, 03:07:08 PM

Its been many years since i worked on a K3/4 but i dont remember any seals, those seals shown by another member have a 333 middle number which is 350/400 four not twin.
Tha top of the guide needs to have a groove to retain the seal if yours are just angled i would check the valve to guide clearance and if ok leave them off

Title: Re: CB350K2 Valve Stem Seals
Post by: McCabe-Thiele (Ted) on July 04, 2026, 03:37:23 PM

Quote from: Craizeehair on Today at 01:50:42 PM

Thanks Ted, I wasn’t sure if it was a must or must not do type of thing. That puts my mind at rest.

The early basic BMC A series engines had no valve stem seals.
Later tuned versions of the engine, Cooper S, MG etc had valve stem seals.
As well as the cost of fitting valve stem seals early versions soon went hard, improvement in seal materials helped.

As Bryan had said the outer part of the stem seals is designed to fit in a groove on the valve guide, do your guides have a retaining groove?

Title: Re: CB350K2 Valve Stem Seals
Post by: Craizeehair on July 04, 2026, 03:56:17 PM

Thanks for the info. I’ll have to check for grooves when I get back in the shed

Title: Re: CB350K2 Valve Stem Seals
Post by: Craizeehair on July 04, 2026, 05:44:44 PM

There’s no groove and the valve to guide clearance is good. I will remove these existing seals and refit without them.

Thanks for your help.