[Clubman Cycles]

I've been avoiding going through the top end on a '73 cb350 twin whos left cylinder has glossed over with oil and burning white smoke. The right side runs like new but the left (from using the side stand most likley) is no bueno no mass. This tells me that the rings aren't wiping right and possibly there's more top end issues (valves, guides, maybe a bore job is needed). Am I correct in my assumption? Before I rip the top end apart and pull out the bore gauge and check the tolerance, I thought maybe someone had some advice for me before I begin. I'm no master mechanic so maybe someone has a lead on a strong motor near NYC for sale? Or an idea of what else it could be? I'm hoping a simple fix like new rings will solve the problem like a hotter plug did last season but I fear the top and even bottom might be shot. Which I would ditch the entire motor and just look for a new one, right? Any advice is always appreciated. Thanks in advance - Joshua

 

[J-T]

After adjusting the valves and a thorough visual inspection a compression/leakdown test would provide a better base of information to proceed on. Unless that identifies something simpler you'll need to remove the top end to determine what needs to be done.

 

[phil71]

you need some better troubleshooting. Is the oil on the OUTSIDE of the engine? White smoke is often a fuel starvation problem, which CAN grenade the motor.

 

[Clubman Cycles]

you need some better troubleshooting. Is the oil on the OUTSIDE of the engine? White smoke is often a fuel starvation problem, which CAN grenade the motor.

Yea there's a bit of oil leakage on the left side of the motor, even up onto the carb. She's not weeping but she's slowly bleeding for sure. If you pull the left plug and shine a bright flashlight into the cylinder you can see it's glossed over where it shouldn't be. The color smoke is 100% burning oil. The bike has no centerstand and has always sat left, meybe the last owner forgot to close the petcock all the time and that's probably why I'm seeing this collapse of the left side?

 

[outobie]

what's compression?
if you have good compression your motor will run
has the motor ever been apart?
have you tried torqueing the head bolts to spec? (14.7 Ft/lbs)

white smoke is typically from over heating, not burning oil.

 

[Simo]

Hi Joseph, welcome (again)
Oil would burn blue smoke,( though colour is subjective) if the petcock isn't switched off every time gas can leak through the carbs into the head and past the valves if they're open and thin the oil. Fuel fouled oil melts cams and causes excessive wear (and oil leaks). Is the bike running cut pipes if so it might have burnt the exhaust valves, which is why the compression numbers are important ( putting your thumb over the spark plug hole isn't enough, nor is the fact that the bike runs , since it may run with compression so low that it can't be ridden )

 

[Clubman Cycles]

Hi Joseph, welcome (again)
Oil would burn blue smoke,( though colour is subjective) if the petcock isn't switched off every time gas can leak through the carbs into the head and past the valves if they're open and thin the oil. Fuel fouled oil melts cams and causes excessive wear (and oil leaks). Is the bike running cut pipes if so it might have burnt the exhaust valves, which is why the compression numbers are important ( putting your thumb over the spark plug hole isn't enough, nor is the fact that the bike runs , since it may run with compression so low that it can't be ridden )

Thanks Simo,
No, the pipes aren't cut however the bike does have an aftermarket 2 to 1 exhaust. Even though I'll never see the return on my investment, I've decided to rebuild the top end and pray it's something simple. As always, I appreciate the input

 

[Simo]

Just make sure you get the compression numbers before you tear down

 

[Clubman Cycles]

Pistons are flawless, no scoring etc. The compression and oil rings are totally shot on this bike. Gaskets too. There lies the rub, as they say.

 

[Simo]

Hopefully the bores still in spec then you can get away with a hone, new rings and gaskets