Blown valve

I recently bought my brother in laws bike after he locked the motor up, its a 2006, great frame, everything looks good other then the valve lodged in the bottom of the crankcase, anyone else have this problem and would there be any reason to open the crankcase, this is my first rebuild on a crf450. head is destroyed from the valve hitting it, piston and cylinder is cracked, warped. and finally found the valve lodged in the crankcase preventing a full rotation

Engine needs to be torn apart. It'll need a new crank, new crank main bearings, piston, cylinder and head. These bikes have very sensitive cranks, and smashing into a valve will definitely compromise them.

 

These cylinders wear like iron, so I wouldn't have a problem with a second hand cylinder, provided it wasn't gouged/damaged. You might be able to get away with a used head, but I'd expect to do valves at the minimum, so it's probably best to get a rebuilt one.

 

Crank and piston will need to be purchased new. Stay away from the Wiseco cranks - they had a lot of issues.

Edited by Lead Head

OEM or Hot Rods cranks are just fine

Bigborethumpers.com Has everything you will need. Crank for $539 Hot rod crank with a carrillo rod. New head for $549 and a block and piston kit for $363.97. Check it out. 

wow these 4 stroke really are these expensive huh?

Bigborethumpers.com Has everything you will need. Crank for $539 Hot rod crank with a carrillo rod. New head for $549 and a block and piston kit for $363.97. Check it out. 

 

Buy all of this, guilt free and then explain to your wife that you were just "helping" HER brother out when you bought the bike.....too easy!!! 

wow these 4 stroke really are these expensive huh?

Not really, if you want to do a plain-jane rebuild, you can get a hot-rods crank for $250, and a piston kit for just over $100.

What he said. Whatever you need in parts hit eBay!

Add a gasket kit and a cam chain to the list

I would ditch that engine track down a cr500 motor to make a cr500af

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