Topic: NO valve seals exhaust side? What next.

[KingCustomCycles.com]

So I am cutting away with my new Neway valve cutters, prussion blue and lapping and whatnot and I pull the exhaust valves out.  No seals, just a tapered cone like end on the guide.  No provisions for seals, no nothing?  What have  I got here?  1969 CB750 K0.

[fmctm1sw]

The early bikes were like that, seals only on the intake side.  My 350f is like that..

[754]

Your life would be so much different with a partsbook.. things really were different in 69!

 Now you got to decide if you want it to remain a KO.. or change it..

[wrenchmuch]

My K1 had them too . I replaced them when I did my head work with guides that take seals . Some oil will leak past the valve stem . Some posts have suggested those guides have less friction than the ones with seals .

[MCRider]

My K1 had them too . I replaced them when I did my head work with guides that take seals . Some oil will leak past the valve stem . Some posts have suggested those guides have less friction than the ones with seals .

Its not so much the guide that has the less friction as the fact that there is no seal there and the seal caused the friction. You could achieve the same performance advantage by simply leaving the seal off of the guides that are made for seals. And risk some low level smoking.  It was one of the litany of things (see HondaMan) which in the aggregate made the early ones faster.

The thought wsa that the intake stroke pulls the oil in thru the guide so seal up the intake guides, and let the exhaust guides breath free. But if you want a really cleaner engine you need to seal the exhaust side too.  With overlap, there is some sucking down there too.

I voluntarily switched to no seals on my project and i may regret it, if its a smoker. But the early CB750s didn't really have a rep for smoking, so i think it'll be OK. I got hold of the original taper top guides. I'm not sure they are still available.

[markb]

I'm a little confused.  My April, 69 parts book calls for 8 seals.  My CB750-K2 parts book calls for 8 seals up to number 14955 and 4 after.  Are you guys saying the early engines didn't have exhaust seals?  Or am I just reading something wrong?

[Magpie]

Here, I'll add to the confusion. My sandcast #260 has provision for exhaust valve guide seals, my 12'69 built, does not. The diecast came with .25 over pistons so it's been apart. I don't know the history of the sandcast.
First picture is the sandcast, notice only 2 holes for the o-rings for the oil passage. Second is the 12/69, notice 4 o-ring holes and no provision for seals on the exhaust guides. I wish these bikes could talk!
Cheers,
Cliff.

[markb]

Cliff, that agrees with what I am saying.  The newest engine I have is an 11/69 diecast with a 12xxx (pre-14955) engine.  It has exhaust seals and so do the sandcasts.

[Magpie]

So they dropped the exhaust seals somtime between 11/69 and 12/69 and then started them for the K1's according to the previous post by wrenchmuch. I haven't had the head off my K1 yet. Cliff.

[tlbranth]

Been a while since I've had an engine in bits but seems to me seals on the exhaust are unnecessary. It's the intake side that gets oil sucked in.

[Old Scrambler]

Several comments on the High-Performance page agree with HM-Mark about no exhaust seals on K0 & K1........I tore down K1 #1045112 and found no exhaust seals.

[markb]

So they dropped the exhaust seals somtime between 11/69 and 12/69 and then started them for the K1's according to the previous post by wrenchmuch.

But it looks like they shouldn't have been there. 

[Magpie]

Yes, very strange. Cliff.

[MCRider]

Several comments on the High-Performance page agree with HM-Mark about no exhaust seals on K0 & K1........I tore down K1 #1045112 and found no exhaust seals.

I had always been under the impression that from the beginning, no exhaust seals. The change came at K1, not during. I can't dispute anyone's evidence to the contrary.

The no-lip guides became unavailable soon after the change. Hence any bike with lip guides and no seals has obviously been apart and the guides were changed. No-lip guides being unavailable, lipped guides were used, and the seals left off.

The discussion led me to review "The Restorers Guide" by John Wyatt (side note: this book is bringing $200 on eBay! I've heard.). It clearly indicates the seals existed in the beginning and were dropped early on around 101xxxx. But they have it restored at K2.

So at least we know they were here, went away and came back. Some confusion (at least to me) as to engine numbers. As noted, they are not needed, but in an emissions sensitive world, provide for a slightly cleaner running engine.

[Hinomaru]

Along with MC Rider ...

The mid-production CB750 parts book shows the different valve seal applications: 

(click on images for a larger view)

[ekpent]

That is some interesting information,funny they would have them,then not and then back again. Good stuff to know and very specific with those engine numbers.

[MCRider]

Wow thanks Hino as usual. That really spells it out.