I have a 1986 250 Moto 4 and I just removed the head cylinder because it would not crank. I can see that the intake valve does not seal because it is not sitting at th right angle. Does anyone know how to fix this?

 

The valve is probably bent. If it is, replace the valve. Usually they are fairly cheap($15), but the installation at a machine shop is around $45 if you cant install it yourself. If the valve is bent, you need to find out what bent it. Usually the timing is off and the piston hit it, so check the timing carefully when you put it back together, and dont spin the engine over with the starter until you know its right - spin it by hand. Trust me, I learned the hard way!

 

There are a few things you must check first. First you gotta remove the valve and see if its really bent. A valve spring compressor tool can be rented at most auto parts stores. Once you got the valve out you can give it a closer look. If the valve was bent you have to take a close look at the head and see if it messed up the valve seat. Also check out the valve guide because bent valves can crack them. Most of the time they bust right where the guide meets the head. If the valve seat looks alright and the valve guide isn't broke you might be able to get away with a new valve and lapping. (lookup valve lapping on google.com if you haven't tried it before) It might not be something you would do on a new engine but if its a backyard cruiser then its fine. If you want it done right you would have a new guide pressed in and reemed out then have valve seat re-cut and lapped to the valve.

Bikebandit.com prices for a 1986 Yamaha YFM225S
Intake valve $12.21
Exhaust Valve $27.98
Valve Guide $24.31
Valve stem seal $9.25