smoking one side on a new rebuild

I just finished rebuilding my 1971 commando. New cylinders, .02 over, new bore and hone, new valves, valve guides etc. I put it together started right up. Left side is real smokey. right is very clean. Compression is 160 on each side but my compression meter has a long rubber hose so my compressions always run low. I blocked off the oil to the head and ran the engine for 1-2 minutes... still a lot of smoke on left.

I really havent broken the engine in yet, but would I have such a one sided problem?
I am thinking broken or pinched ring, upside down ring or bad head gasket. I am sure its not the top end. Any other ideas? Should I run the bike a while or just plan to open the engine up?
Thanks for your input
Gary

Is it on the center or side stand? If side stand, don't do that .

Start it up let it run a few minutes, turn off and quickly take the intake rocker cover off and see how much oil - the drain is on the right so if clogged the left is more likely to have oil problems if the valve seal is bad.

Of course, might just be burning off oil from building. Once the valves are eliminated, I would guess upside down ring.

Its a 71, so I scrapped the sidestand. Its on a rack on the center stand. It seems to have a normal amount of oil in the head and it drains fine. I am pretty sure its not the head. I guess my question is would I get that much smoke, one sided, just after a build from burn off? I feel I have run the bike long enough for burn off.

I will see if anyone has any other ideas otherwise I will take the bike apart in a day or so.

qside said:

Its a 71, so I scraped the sidestand. Its on a rack on the center stand. It seems to have a normal amount of oil in the head and it drains fine. I am pretty sure its not the head. I guess my question is would I get that much smoke, one sided, just after a build from burn off? I feel I have run the bike long enough for burn off.

I will see if anyone has any other ideas otherwise I will take the bike apart in a day or so.

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Is it puffing a little smoke or acting like an old diesel truck? If it's not enough to embarrass you to ride, I would go for a ride and see if it cleans up but I agree is seems like you run it enough. If not, I'm guessing rings. Oil can really only get in the cylinder two ways besides what you put in while building.

BTW, if you remove the plugs and kick, do you hear the sump venting? Unlikely to be one sided but a blocked sump vent might do it.

I once had exactly what you describe
It turned out to be the very end of the expander on the oil control rings was missing

I have a feeling it is the the oil ring. I had a hard time getting them to compress. I plan to open the engine this weekend

Scenario sounds very familiar, it was a valve seal.

Just to finish up the discussion. I opened the engine yesterday. The left side oil scraper was ineffective. It was a 3 part ring with the thinner metal strips. I replaced it with a 3 part with thicker strips, changed the head gasket and closed her up.

I started her up and no smoke!
It was a good day.

Good to know you have found the problem.