SOHC.co.uk Forums > CB750

smoke, stem seals, rings or oil pump?

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Graeme77:
My 750f1 smokes when you start it up.
I know smoke on start up/over run is normaly valve seals and smoke when accellerating is normaly rings.
Mine smokes when you start it but sometimes a little and clears quick and sometimes alot for ages.
It did used to wet sump alot but going over the pump seems to have sorted that.

the longer it sits the more it smokes on start up.
Ive never had the motor apart but someone did (I have reciets), 12 years ago but its only done a couple of thousand miles since then.

I have just put the bike back together after restoration.

If this is stem seals, no big deal I guess. Rings more of a pain and im sure its not that, but does it sound like its still wet sumping enough to smoke? Can I get pump seals etc to cure it?

If parts were cheaper and access was better id just go through the engine but I dont want to take engine out if its just the pump, not sure there is anything I can do to the pump anyway.

Tempted to just ride it as is but its also a pig to start if its been left a week (oiling plugs?)

Any thoughts?

Bryanj:
What you describe is more likely stem seals or rarely a cracked valve guide if it ha been mishandled during rebuild, rings are less common but if you take the head off to do the seals it is false economy not to lift the cylinders as the base gasket will probably leak later as the same studs clamp both

Graeme77:
I would have left head on to do the seals.
Otherwise as you say, might as well remove cylinders, do rings, may as well open bottom end and to primary chain as its almost on the limit.....


Trying to avoid all this at the moment hence wondering if it sounds more like its burning oil from wet sumping.

Graeme77:
Are the stem seals in the gasket sets any good?

steff750:
 ;) i have to say id be very surprised if wet sumping is your problem,
 all my cb750's wet sump if left long enough but not all of them smoke .although the old britt bikes are a prime example of what you are experiencing
 i would try a compression test first and you will probably get your answer   ;)

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