Oil weep from head

[royhall]

Hi. My CB350F (the one in the Avatar picture) has started a slight oil weep from the right hand side front of the cylinder head. Leaking between head and barrels. I know Trigger recommends an o-ring thicker than standard at that point which I can't fully remember if I did (done a lot since then). Is it possible that the head just requires re-torquing down, and if so, is it safe to slightly over torque like recommended for the 750. Or should I just take the head off again and fit another new gasket and o-rings. The bike has only done 400 miles since its rebuild years ago. Cheers.

[SteveW]

http://www.sohc.co.uk/index.php/topic,28673.15.html

This is my post about the subject, it was for my 650 though.

I’m in the process of rebuilding my 550 at the moment so I’ll probably go for thicker o-rings again.

[Oddjob]

When it was rebuilt Roy was an original Head gasket fitted or an aftermarket?

The problem about advocating thicker orings is that if they squeeze inwards they will restrict the oil passageway and you an imagine what they could cause.

Plus IIRC the 350 used an odd looking oring around the restrictor jet in that location. Which I would imagine means finding a thicker one a real problem.

Honda never advocated retorques in my experience, doing them on a 750 for example would be a nightmare.

[royhall]

Cheers Ken. If I remember correctly the head gasket is Athena/NE, but it's so long ago I cant remember if the o-rings were standard or thicker. The oil jets are no problem as there's good flow to the head. I may as well re-torque the head before I take it off. If it takes a re-torque to 21.6NM because they have come loose or the gasket has compressed I will give it another go. If it wont torque up anymore I will take the head off and have a look.

[Nurse Julie]

I would try a re torque, you have nothing to loose by giving it a go.

[Oddjob]

I thought the orings were that odd shaped?, like a turtle neck sweater top, I'm wondering where you managed to source oversize ones of those. I wasn't concerned about the restrictor jets, more the orings surrounding them.

There is an old dodge the American mechanics came up with which they reckoned solved the problem, at the time we didn't adopt it in the UK as the product they used wasn't readily available over here but it is now. I'll leave that until we see whether the retorque works. It will involve a new head gasket though I'm afraid.

[magpie114]

Following with interest, my 350 came complete with oil weep between head and barrels.


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[royhall]

Scratch that about the extra thick O-rings. Done that many jobs in the past few years my old brain is a jumble. Looking back at old posts shows that the thicker O-rings are for the 750. Dementia strikes again.
A re-torque would be nice as it's quick and easy. No need for taking off air box and carbs or the exhausts, plus it doesn't cost anything.

[Bryanj]

You can try it but i have my doubts

[Oddjob]

Yeah me too Bryan, it works very rarely in my experience. BUT, worth a pop.

[K2-K6]

It'll be interesting to see Roy if they rotate any more from their position as they are now, suggesting some compression of the gasket has taken place.

To re torque anyway there's always debate over method. Absolute accurate torque SHOULD be achieved by backing the nut off and then tightening to the figure you want rather than adding torque to an already set stud. This done one at a time with all the others still tight. Thats if they dont display any looseness as above comments.

With persistently leaking gasket faces (if there's a general history of slight leaking over many examples) I use hylomar spray, yes a very thin "sellotape" type coating on both sides of gasket, degrease the faces immediately before installation with isopropyl or  MEK to add sealing security to that type of gasket.

Outside end of 750 F2 head gaskets are firmly in this area from my contemporary experience 

[Laverda Dave]

Interesting thread with some excellent ideas. Am I right in thinking when the 350 was taken out to 400 the length of the head and barrel studs remained the same and this caused the same symptoms to the 400 with a potential weep between the head and barrels. Honda cured the problem by fitting longer studs to provide more pressure on the head gasket? Did this factory mod actually work and from what engine number were the longer studs fitted and how much longer were they compared to the originals? Can the longer studs be retrofitted to an earlier engine (I would imagine this could be difficult as the existing studs are likely to be corroded into the upper crankcase).
Nigel, your idea sounds good, I'm thinking of doing this when I come to rebuild my engine as I'll be fitting a NE head gasket 👍

[Oddjob]

IIRC Dave, Honda changed the head gasket for the 400 and applied a layer of silicon to the gasket, especially around the oring part, it's that shiny slightly sticky surface you can see and feel. That appeared to work but of course aftermarket gasket don't have that as a rule. The 500 original gaskets also have that coating.

[royhall]

Sorry it's taken a while to update, I have a friend who has terminal cancer so I have been busy reassembling his Kawasaki ZXR750 so he can sell it.

Finally got round to the 350F last weekend and got the cam box off and down to the head bolts. On original assembly, the head bolts were tightened to 22.5NM in the correct sequence, going through 3 stages then left 24 hours and torqued again.

On checking them now, some are barely past finger tight and non were still at torque. So again I have torqued them down in stages this time to 24NM. They were loose, really loose. Following reassembly the bike started first time (that had become rare) and no obvious oil weep, it also ran really well. When I looked closely at the gasket it had mushroomed out of the joint slightly which is unusual. I think it was an Athena head gasket that I have since read bad reports about. It does look to be a good bit thicker that a standard Honda item. Anyway, it's good now just hoping it stays that way.

[Laverda Dave]

Did you loosen all the nuts before the re-tourque to 24NM Roy as Nigel suggested or did you just re-torque from where they already were?
Interesting to hear about the Athena gasket as I have not had a problem with them in the past and I understand they are OEM to a lot of Italian bikes. I’ve bought NE brand for the rat bike rebuild as Athena were at least twice the price.