Smoking after rebuild

[Nelson]

I just rebuilt my XS650 with the following mods:

750 CC big fin Cylinder block and 750 cc pistons and rings
Turned Crank 83 degrees
Cut/welded cam shaft for new timing
High output Alternator
Custom 2 into 1 exhaust out the left side

Bike has a Velorex 562 sidecar attached. Mods to bike include all three hubs laced to 15" Car wheels so I can run car tires
Custom Leading link front end from Dauntless Sidecars

Problem: Engine fired right up on first try. Got everything hooked up ran it a few times then took it on a couple of spins around the block. Everything seemed OK and it was pulling strong. Did a valve adjustment and checked everything out then had my wife hop in the side car to go for a spin. We got a few blocks from home and pulled up to a stop sign when it suddenly started puking white smoke. A lot of white smoke. Immediately headed home and pulled the plugs. Right plug looked fine, left plug was oily. Checked the compression right side was good, left side was low by, as I recall, about 15 PSI.

I have taken the engine back out and pulled the cylinder block. Inspection of the cylinders shows nothing obvious. Inspection of the pistons and rings shows nothing obvious. rings (which were new) look fine. End gaps are properly spaced. Head has new valves and valve guides and I can't see anything obvious.

Does anyone have any ideas on what I should look for? I am about to just buy another engine (stock 650) to throw in it so I can start using the bike, but I really would like to get the 750 engine running properly as I can really use the additional torque pulling a sidecar.

 

[Jan_P]

I yesterday mentioned on another thread the tight valve stem play after a rebuild and not much lubrication in the beginning
Having the theory high revving adding heat and the already tight play can change creating more heat
and also Perhaps check so the valves are straight

 

[Nelson]

I yesterday mentioned on another thread the tight valve stem play after a rebuild and not much lubrication in the beginning
Having the theory high revving adding heat and the already tight play can change creating more heat
and also Perhaps check so the valves are straight

Thanks. I guess my next step is going to be to compress the valve springs and take the valves out so I can inspect them and the valve guides. Everything was new when I reassembled the engine after having the valve seats ground. I installed new guides and new stainless steel valves but there are not too many ways oil can get into the cylinder and valve guides is one of them.

 

[gggGary]

Head gasket leaked?

 

[Its been a long time]

White smoke isn't oil? White smoke is more likely unburnt fuel?