Why is My Motorcycle Blowing Out Blue Smoke?

What could be causing your motorcycle to blow out smoke after the pistons and rings and valve seals have been replaced? You may have overlooked one important valve train component.

Partzilla’s motorcycle expert John Talley hosts live Q&A sessions on our YouTube channel every Friday at 3pm Eastern. In this session, John was asked what besides the piston and rings and valve seals could be causing a motorcycle to blow blue smoke.

Motorcycle blows blue smoke causes

Motorcycle Blowing Blue Smoke Q&A

I've replaced the piston and rings and I went over bore, and I also replaced the valve seals, but my motorcycle still blows some blue smoke. What else could be causing my bike to smoke?

John Talley: Alright, it sounds like you’ve addressed everything except for one thing: the valve guides. Because if the guides or the valve stems are that worn out, even new seals will possibly let oil shoot up there, or down through there. That may be what it’s doing, and it’s probably going to be doing it on the intake stroke. So when it goes to take a big gulp of air, well yeah, it’s pulling through that passageway and going out through the carburetor, or throttle body. But it’s also going to try to pull whatever it can past the seal and the valve. And if that valve stem or the guide itself are worn out, then you’re going to have a problem. Go back and think whether you had any play on the valve itself when you were replacing it. But that would be the place I would think to look.