SOHC.co.uk Forums > CB750
Crankcase seal leaking
Rob62:
Just out of interest blasta, you may want to look at the link below. The seal you have bought has no lip but has the correct part number?, i’m no expert on honda parts but it may be that the replacement seals are lip free to enable fitting without stripping the motor, if this works then you will have saved a ton of work or money.... so imo worth a try. However it does look to be pretty crappy around that seal so if it looks bad in there once you remove the old one it may be better to strip the motor anyway. Have a dig and see what you think. Good luck!
http://forums.sohc4.net/index.php?topic=74771.0
K2-K6:
That one on the net site's interesting, as pointed out above by Bryan they don't usually leak there. It's possible that both this example and Rob's posted one area suffering initially from crankcase pressure build up as someone has mucked about with the breathers on the USA one.
We had on here about 4 or so years ago a (can't remember who's it was) blue 750 K2 in Kent that had the breathers connected wrongly and kept pushing oil out of different places, corrected those and went away.
It looks like previous owners go straight for the seal and make a dog's dinner of it.
If you want to put an original lipped seal into it, put one of those smooth stainless jubilee clips around it, after first greasing with silicone, then place this against the cases and push the seal through with a drift. The rubber flange is just that and not supported by a steel lip inside (you'd have to check this).
The purpose of the lip in car crank applications is to make it, to an extent, self sealing against crankcase pressure buildup and stop oil pushing past the outer edges. They are normal at the flywheel end to make sure the clutch doesn't get contaminated.
I'd still split this one to get a better longterm fix though, it's not that hard...... Is it?
Trigger:
I think if you wrap some draft excluder round the end of the crank it may work, well it keeps drafts out ;D ;D ;D
K2-K6:
If the engine's that windy, may need that on the piston rings ;D
Blasta:
Thanks for all the advice, and thanks Rob62 for that link. All very interesting.
I've had the bike for about 6 months and the guy I bought it from had rebuilt the motor. He's in his 60s and has been riding/racing/rebuilding 754s since they came out in the 70s.
He did the motor many years before I bought it off him and sorted all the rest of the bike, I've done 1600km since.
I spoke to him after I posted this thread and he's offered to help me take the motor out and replace the seal. He also thought that the alternative option would probably work, and after reading the thread that Rob62 posted I think I agree. I think it's worth trying, if it leaks I'm really no worse off and I'll take him up on his offer.
So now I just have to get the old seal out, and as you can see from the pic I had a go yesterday and was unsuccessful. I'll have another go and let you guys know how it turns out.
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