Just got an 86 Yamaha 225 Moto4 for $100. Seller said it ran when they last used it 10 years ago. I put a new battery in it and the lights work and neutral light works. It seems to shift fine. However I think the piston is seized up from rust.

What is my best option? I put some oil in the spark plug hole to let it soak a little while ago. Can I remove the top end without taking the entire engine out?

 

Can you try and pull start it? Or is it defiantly seized?
I have a soft spot for these old machines. I have an '88 that I first learned to ride on

 

You can almost always get the head and cylinder off with the engine in the frame but you won't get the cylinder off if it is stuck to the piston. I would try taking the pull start off and rocking the crank gently backwards and forwards with a bar. Diesel fuel or easing oil down the plug hole is recommended by mechanics. Leaving for a couple of days to soak before freeing off is a good idea. If it is still stuck, take the head off and knock the piston down the bore with a block of wood as a drift.

 

I tried the rope starter with a strap wrench and have had penetrating oil in it for a week. I will try taking the head off. This is my first engine project ever so I appreciate the help.

 

Success! Top inch of the cylinder has rust on it, but I will use some 180 grit to see if I can remove it. Now on to the carb rebuild

 

I have the same quad.

Regarding its former carb problems: https://atvconnection.com/forums/yam...00-carb-2.html