oil out of head

Last year I redid the head on my 850. New valves and guides and to boot I also put in new pistons and got the barrels honed to 20 tau over.
It rides great but it throws oil out of my left cylinder exhaust port. I was hoping that it would go away or get less by riding it so I put about 2000 miles on it but it still does the same nasty oil leak out of my exhaust port. Before I take it all apart again, do any of you have an idea what the cause could be? Valve guide? The rubber seal that sits on top of the valve guide?
It doesn't smoke much (such so now and then when I pull up) but the left side of the engine (including my left leg) is getting plenty of oil on the outside...

Thanks in advance for any suggestion.

It may not be the exhaust valve (guide or seal) leaking oil. The Commando is famous for leaking oil at the joint between the cylinder and head. The oil wicks up the 5/16" studs and appears between the third and fourth fin on the head. Try cleaning the head thoroughly, then run the bike a short time. Check the area around the studs carefully. You might use baby powder. My guess is that is where you'll find your oil leak. The fix, assuming the head surface is flat, seems to be sealing the offending area. One method I saw posted here was to circle the pushrod tunnel area on the gasket with sewing thread after applying a sealant. I do know from experience that installing a PCV valve all but stopped the head from leaking .

JimC said:

It may not be the exhaust valve (guide or seal) leaking oil. The Commando is famous for leaking oil at the joint between the cylinder and head. The oil wicks up the 5/16" studs and appears between the third and fourth fin on the head. Try cleaning the head thoroughly, then run the bike a short time. Check the area around the studs carefully. You might use baby powder. My guess is that is where you'll find your oil leak. The fix, assuming the head surface is flat, seems to be sealing the offending area. One method I saw posted here was to circle the pushrod tunnel area on the gasket with sewing thread after applying a sealant. I do know from experience that installing a PCV valve all but stopped the head from leaking .

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I heard of another old trick - laying dental floss around the joint. Supposed to work great on engine case joints.

Too bad I didn't learn this until after I assembled mine - but will remember for the next one :wink:

Doesn't smoke much :?: it shouldn't smoke at all after a rebuild like that,are the plugs and pistons dry.It is possible for oil to weep through from the spring recess and out the exhaust port if the head is porous or cracked or loose valve guide. Thats the worst case scenario but worth while rembering if all else fails

That thread idea sounds much easier than O ringing the tunnel. Another fix from long ago was to score a circle around it to hold sealant.

JimC said:

It may not be the exhaust valve (guide or seal) leaking oil. The Commando is famous for leaking oil at the joint between the cylinder and head.

Click to expand...

Especially with a copper head gasket.