250ES smoking after rebuild

[JS1987]

Hello all, I am new to the group and had a question maybe someone can help me out. Recently picked up a 1987 250ES that’s in pretty good shape and runs good but SMOKES like real bad. Previous owner did a top end rebuild and posted a video of it so I have proof he’s not lying. Anyways he had the cylinder machined, replaced rings, replaced valve seals and lapped valves, cleaned the head up real nice and no change. Still smokes like a chimney, I’m kinda at a loss previous owner was saying the crank oil seals needed to be replaced but I’m not sure. He ran it for awhile after rebuild to make sure it wasn’t just in the pipes and I have not done a compression test yet. Any help would be appreciated!

[shortline10]

Their are no crank oil seals on that motor that would cause it to smoke .
I can guess all day long on what it can be but in the end the topend needs to be pulled and inspected .
Check the valve seals and piston / cylinder for scoring . It should be pretty obvious if it’s smoking that badly .

[JS1987]

That’s what I wanted to hear thank you, I took the front inspection cover off and rolled it over on the starter, noticed that a lot of oil pools up where the exhaust valve is so I’m hoping for a valve guide/seal. It’s possible he could have torn the new one when installing

[Az200x]

Sounds like a seal just as you stated, what’s the verdict ?

[ATC200X4716]

Also curious what you find. In my experience, smoking like a chimney is the rings. The valve to valve guide clearance is relatively tight and usually won't leak that much oil through, but you never know. I've owned many bikes over the years and don't think I ever solved more than one or 2 smokers with just valve seals.

[New Sox]

ever resolve this issue?

[ATC200X4716]

Any news? I'm betting on cylinder. If anyone needs a cylinder properly bored/honed let me know.