Joined
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43 Posts
CB350K3 1971
OK so I bought this bike with a smokey left pot, and a very oily muffler.
I checked compressions and they were way down below 150psi, and I had to take the bore out to final oversize to remove the ovality and fitted new pistons and rings.
Compression now at a healthy 180psi

Started up and we still have smoke, :twisted: so for me the only thing left to cause this, is a worn valve guide/valve.
Sure enough removal of the inlet valve saw a lot of burnt oil on the back of the valve face, result!
Now I cant do this sort of thing as the guide has to be reemed out to the valve diameter. So the head went off to a specialist who suggested fitting a phosphor bronze sleeve.
He calls me later that week and says that the guide diameter is within tolerance, no need to fit a sleeve, and fitting a new valve would solve the smoke issue.
Engine back in and started up, after about 5 mins (or once the engine gets warmed up) the smoke returns, just as bad. :twisted: I then thought ah! maybe the header pipe is oily and I need to clean it out, so I did that and still no good.
Anyway I have a couple of questions please.
Has this "specialist" got the specs wrong?
Is there another point of possible oil ingress?
I'm going to get a second opinion from a honda CB 350 race engine company. But I thought I'd ask here for some advice, as the engine is coming out
OK so I bought this bike with a smokey left pot, and a very oily muffler.
I checked compressions and they were way down below 150psi, and I had to take the bore out to final oversize to remove the ovality and fitted new pistons and rings.
Compression now at a healthy 180psi
Started up and we still have smoke, :twisted: so for me the only thing left to cause this, is a worn valve guide/valve.
Sure enough removal of the inlet valve saw a lot of burnt oil on the back of the valve face, result!
Now I cant do this sort of thing as the guide has to be reemed out to the valve diameter. So the head went off to a specialist who suggested fitting a phosphor bronze sleeve.
He calls me later that week and says that the guide diameter is within tolerance, no need to fit a sleeve, and fitting a new valve would solve the smoke issue.
Engine back in and started up, after about 5 mins (or once the engine gets warmed up) the smoke returns, just as bad. :twisted: I then thought ah! maybe the header pipe is oily and I need to clean it out, so I did that and still no good.
Anyway I have a couple of questions please.
Has this "specialist" got the specs wrong?
Is there another point of possible oil ingress?
I'm going to get a second opinion from a honda CB 350 race engine company. But I thought I'd ask here for some advice, as the engine is coming out