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CB750 K3 Oil leak
Seamus:
Are the head bolts stretched? What value are you torquing up to? I fitted some high tensile bolts (Ape I think) and these allow a bit more torque. May be worth thinking about
Cheers
Seamus
K2-K6:
Hi
Had a chat with pete about this at the ace cafe 70's day last month. I've only ever had total sucess with this by using blue hylomar very sparingly (you never want ANY loose sealant to get into oil ways) worked on them quite a lot in 70's and 80's and always used this method. Clean surfaces completely, no old gasket trace at all, use isopropanol alcolhol for final clean, was easier to coat gasket both sides rather than casting, standard studs / torque + pattern etc. Friend has an original 750 F2 and is the most particular person that I know and I must of helped him lift that engine out about six times and put it back again as he insisted on doing exactly as the manual said i.e. no sealant, eventually persuaded him to go with hylomar and it didn't leak. These were all Honda original gaskets (one of the pull out's was to do valve guides as well as leak).
As you know it's a bit of a pain on these as it's motor out each time, all the notes about other leak points are also relevant.
I believe that if you use stronger studs you have the "potential" to distort main bearing area as Honda must have designed it to accept the loadings it required.
I would take a guess that the surfaces were absolutely degreased on factory assembly so this may be a reason why they can work dry with original gaskets so worth considering
Bryanj:
Very original gaskets had some sort of a "Sticky" coating on them arround the chain tunnel and oil feed areas
sim2011:
Thanks Brian
I'll wait and see what Honda send me, The engine will be out tonight so I should be able to post where its leaked
Thanks
Simon
K2-K6:
As Bryan said the originals had a coating that looked shiny and had a feel that was rubbery/tacky to the touch around critical areas, I guess with a really clinical degrease this should work and I can never recall a factory built motor leaking in normal circumstances.
I'd be VERY careful about taking a skim if you can avoid it. This changes (albeit mildly) cam timing, compression, valve to piston clearance etc and may require special base gasket to regain correct dimensions.
In my experience these are very stable castings and unless they've been butchered then normally remain stable and flat. I'd have a careful check initially with a good quality steel rule to see if you can spot any thing other than flat and consider from there.
They are not easy to skim as you have steel liners in ally for the barrels so getting a clean cut takes someone who knows what they are doing, plus the head i think has to sit up on spacers to mount flat (avoiding protruding valve guides) this is quite different to car components and may present you with some problems and potentially scrap the castings.
I'd say the hylomar route was much less risky. Our reasoning behind this was that they leaked at the point they do because of a non-adhearance of the gasket to the surface (you can usually lift the gasket straight of fwith no visible residue and see the oil path during strip down) so if you can get it to adhere with on spec gasket / degrease then great.
When you take them apart from original assembly those sticky areas usually showed sign of the gasket tearing with a thin part of the surface remaining on the casting, confirming to me that Honda required them to be physically bonded hence the gasket treatment.
It'll be interesting to see what you find, it's just fiddly wiggling the motor out without scratching any part of the frame!
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