Is this normal...leaky valvetrain??

My 04 250f has ben smokin blue pretty bad, especially when first started after sitting awhile. The bike has also been getting harder and harder to start. Otherwise it runs real good with awesome power. I decided to open up the top end for a look...my first time but not the bike's cause I bought it used.

To me, the piston and cylinder look decent and the ring gap is 0.013". The valve clearances were 0.004" and .010" (0.001" under spec). What concerns me is all the carbon buildup and traces of wet oil around the exhaust valve stems in the exhaust manifold. It is a real mess in there! Could it be that everything is ok except the valve seals which is causing the oil burning? Is there a minimum spec for the piston skirt? WHat is the best way to clean all the crud from the head and valves?

Thanks!

My 04 250f has ben smokin blue pretty bad, especially when first started after sitting awhile. The bike has also been getting harder and harder to start. Otherwise it runs real good with awesome power. I decided to open up the top end for a look...my first time but not the bike's cause I bought it used.

To me, the piston and cylinder look decent and the ring gap is 0.013". The valve clearances were 0.004" and .010" (0.001" under spec). What concerns me is all the carbon buildup and traces of wet oil around the exhaust valve stems in the exhaust manifold. It is a real mess in there! Could it be that everything is ok except the valve seals which is causing the oil burning? Is there a minimum spec for the piston skirt? WHat is the best way to clean all the crud from the head and valves?

Thanks!

I'd rebuild it all. Piston and ring set is less than a hundred bucks. The valves will be more but at least you'll know its as good as new.

Minimum size for piston skirt is 3.067 inches - new is 3.0701 inches. But your bike being an 04, I would just go ahead and replace the piston, rings, wrist pin, and clips... The piston will probably be worn below the service limit, and it is just good measure to replace it all. I like the JE 13.5:1 piston kits, $150 at the TT store. Good power boost, and works perfect on 91+ octane pump gas.

Your valve seals are probably worn. You could clean up the valves and replace the valve seals. But if the valves are on their way out, or already are getting tighter and tighter, it is time for a valve rebuild. This entails of getting the guides checked, valve seats cut and installing new valves, seals, cotters, springs, and retainers. Faction MX has a nice intake valve kit. Go all OEM for exhaust.

If you need to do the valve rebuild, Mongoose machine and engineering down in Vancouver BC is probably the closest and most reputable machine shop in Canada for motorcycle work... Or you can ship your head down to Michigan and get Ron Hamp to cut the valve seats.

Make sure to check you cylinder skirt. They have been known to crack. If you're looking for replacement, 05' and up fixed the issue.

Thanks for the help guys! Gonna strip the head tonight and see how everything looks.

What's the best way to clean all the scaly carbon buildup from valves, head etc?

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