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Hello got a 1980 kz750e and I rebuilt the engine by the manual this winter after finding a slipping starter clutch. I did the timing chain and piston rings while I was in there. I initially got the timing a little wrong but it obviously never started with that just spun with the starter. I cleaned and rebuilt the carb and got new cv boots for the slides. The bike runs but it blows smoke terribly and leaks oil from the exhaust on cylinder 2. I think I hear a valve tap when I runs it but it has no stutter or lag with throttle. With the rings being new what is the most likely cause? Could the valves be leaking? When I spun the engine timed wrong could I have damaged the valve? Any help is appreciated. I don't want to start looking in the wrong place.

Could be a broken ring. Did you replace the valve guide seals?
Steve

No I did not, the clearances were good so I didn't touch them but I did get them with the gasket kit.

You do a lot of work on your engine but something gone wrong. Did you offset the Piston ring openings 120 degree of each other?
Cam Timing okay? Valve clearence in spec. Got new valve seals? Compression test? Got a Service Manual? A short Video/pics would help.
I know, a lot of questions but necessary.

Yes I spaced the openings on the rings, yes I timed the cams correctly by the service manual, yes I checked the valve clearances. Did not dio the seals, perhaps I should. It's not that hard to take the head back off and I could see if I damaged a valve by spinning the engine with the timing off about 15 degrees on the exhaust originally. Would getting a bore scope be worthwhile to see if I damaged a piston? Seems unlikely since the engine runs fine without hesitation.

15 degrees is quite a lot to be out on timing. Did you try turning the motor over by hand prior to turning it over on the starter motor? Is it leaking oil from all the exhaust ports or just one?
As its smoking its either rings, valves or valve stem seals.
It sounds suspiciously like you may have slightly bent your exhaust valve/s. Time to take the head off at least and see what you did.

Re check the valve clearance...... a bent valve will show up by going from .005 to .013 .

Matty-face wrote: ...1980 kz750e and I rebuilt the engine by the manual this winter ... I did the timing chain and piston rings... bike runs but it blows smoke terribly and leaks oil from the exhaust on cylinder 2. ... no stutter or lag with throttle. With the rings being new what is the most likely cause? Could the valves be leaking....

blows smoke terribly and leaks oil from the exhaust on cylinder 2. ... no stutter or lag with throttle. With the rings being new what is the most likely cause? Could the valves be leaking

Possibly the new oil ring in cylinder 2 was inadvertently broken during installation.

Leaking oil from #2 exhaust is likely due to improper sealing of the header pipe flange to gasket to port. Port should be clean, assure old gasket(s) removed (sometimes two old gaskets are used instead of one new gasket); can also apply high temp copper seal to hold new gasket in position during installation of the header pipes. When properly sealed, it won’t leak oil at the header pipe to exhaust port junction regardless of oil passing through the exhaust port into the header pipe.

I wouldn’t suspect a leaking valve to be causing the excessive blue exhaust smoke. But would suspect failure of combustion in cylinder #2 resulting from spark plug fouling due to all the oil getting into the combustion chamber via a broken oil ring and/or a seriously leaking valve stem seal.

Spark plug failure in cyl 2 often results in failure of combustion in cyl 3 also, because there's no high tension voltage in the secondary loop, which high tension voltage is supposed to fire both of these two spark plugs #2 and #3 in the secondary loop.

Good Fortune!

Just for my own curiosity, how does one check valve stem seal clearance.

Don't know why I bother.

sounds like oil ring rolled over.