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Cam Chain replacement in CRF150r

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I bought this bike in river bottom condition and have been gathering parts to put it back together.  The bike has thrown the cam chain and has destroyed the top end of the motor.  It has happened more than once as the PO had epoxyed the head cover previously before destroying the head/cyl/piston.  What would cause the cam chain to come off?  The tensioner checks good as well as the the lower gear and guides.  I intend to put a new cam chain in with the new top end.  Crank, connecting rod check good.  Can this be done without splitting the halves?  The manual seems to miss this topic entirely only referring to the cam chain as being removed when accessing something else.  Thanks in advance, Aaronimage (16).jpeg 

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Cam chains are a wear item and need periodic replacement; don't think the manual specifies a replacement interval. I ride recreationally, so I just change the cam chain with the piston over the winter.

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Cam chains are a wear item and need periodic replacement; don't think the manual specifies a replacement interval. I ride recreationally, so I just change the cam chain with the piston over the winter.

I totally agree with the cam chain being a part of routine maintenance.  Can it be changed with splitting the case?

 

Thanks Aaron

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I totally agree with the cam chain being a part of routine maintenance. Can it be changed with splitting the case?

Thanks Aaron

No need to split cases or pull head... Remove magneto cover, flywheel and cam gear.

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The stock cam chain adjuster is automatic and shouldn't need any tweaking.

As a side note on the original topic, I read that some people were able to remove their cam chain without removing the cam sprocket by simply removing the cam chain adjuster. I was hopeful this would work as I have a slotted cam sprocket and removing the sprocket requires retiming the valvetrain. Even with the cam chain adjuster removed, I am not able to get the cam chain on without fear of breaking something. It's just too tight. I'd say if you can get your cam chain on and off without removing the sprocket, it's definitely time to replace the cam chain. 

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If it is ticking check your valve clearances. 

Like KLX said, if you can remove the chain without removing the sprocket, get a new chain.  You can get the cam chain off by removing the whole cam assembly, but getting it back on with the right timing is a challenge.

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