[redblk63]

My 1971 K1 SL350 is smoking from the left tailpipe. The conditions are:
With a hot engine, after I coast downhill with the throttle closed, when I twist the throttle a cloud of blue smoke comes out that pretty much covers the width of the traffic lane. These days, with the fires at all points of the compass, we do not need any more smoke in

The normal guess is a bad valve guide or oil-control ring that allows oil to be sucked into the combustion chamber under high vacuum. The left plug fouls with oil, so it is not leaking through the exhaust valve guide into the Xpipe.

By the way, the compression pressure is a healthy 180/170 pounds for the right/left side.

Engine history: About 2000 miles ago the left piston dome melted because of a lean mixture. I replaced the head with a used one, honed the cylinders with a hand drill, and installed 2 new pistons.

Am I correct that there is no valve stem oil seal on Honda 350 twins? Is this most likely a badly worn intake valve guide or a broken oil ring?

Thanks,
Larry in Pasadena

 

[CB750F]

My guess is the valve guide for the exact same reason you stated. Really if you pull the head it's not much more work to pull the jugs and check the oil rings.

 

[redblk63]

Thanks, 750F. I also think I am wrong about it not being an exhaust valve seal because oil is getting on the plug. Having rethunk, I believe the cylinder is still pulling a vacuum when the exhaust valve opens, during coast-down mode.

So once I get the CB77 engine off my workbench, it's time for probably a valve job, and a ring check on the 350.

Any word on whether the 350 twins have valve seals?

Larry in Pasadena

 

[CB750F]

I'm thinking they do. Hopefully the guides aren't shot. if they are the same size as CB750 seals I believe I have some new ones somewhere. generally engines only need them on the intake valves.