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my bike has found religion. It has a holy piston! NEED HELP!

2 posts in this topic

well... it seems I have a slight dilemma. went on a nice ride the other day with the wifey and after packing us around through middle of nowhere logging roads, the bike waited to complain until we were next to a frequently traveled road. we were cruising along at a good clip (80% throttle) and it felt like it was seizing up or getting too hot. I pulled the clutch in immediately and the engine died and then we coasted to a pull-out. To make a long story a little longer, we pulled the engine and found that the left exhaust valve had broken off and rattle around poking a couple valve shaped holes through the piston. Hallelujah!! Checked the cylinder walls and the action of the religious piston. It still slides smoothly and the walls were well oiled and had no noticeable issues. The head has issues, but the other three valves themselves seemed fine.

Now to the good part!

What do I need to replace/repair besides a new piston and head and valve?

Is it a good idea to use a used head (if I can find one)

Anyone have one?

Should I overbore and go to a 628 or something while I'm at it?

Can I use the same cylinder and a new piston and rings without boring or honing the cylinder?

Any other questions I should be asking?

Thanks in advance for your help! :)

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Why not repair and use your original head? change out the valve that went it's own way, boring or stock is up to you! I would, if changing only th head install new rings and hone thge cylinder while you have it apart. That way when it goes back together it is a new top end.

Only worry I would have is why did that valve break off in the first place......and only one? why not both exhaust valves? sounds as though the cam chain may have jumped a tooth and thus allowing the valves to meet the piston - face to face .....

Fer sure inspect the cam timing when it goes back together - make sure it is dead on.

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