CRT 250 timing problem

I have a timing problem maybe someone can help me with. My sons bike locked up, after i tore it down i saw the timing chain was loose And the valves were against the piston, I took it apart lined up all the timing marks, rotated by hand and the valves still hit, I rotated 180 and the same problem. If I advance one link the motor turns normally but doesn't start. Any ideas???


If the valves hit the piston while running, don't bother jacking with it any more..... it has to come apart. Once you replace all the parts that broke, get a service manual. That shows you how to get the piston at TDC and then line up the marks on the cam drive sprocket.

I lined up all the marks, just like the manual said but they still hit. I can't see anything bent or broke. Could something else have slipped? Should I replace the piston, and get new valves and get the seats ground? Do I need to replace anything lower than the piston?

Cam sprocket is press fit to camshaft.

The sprocket likely slipped on the cam.

If something stopped that motor that fast you probably have bigger problems to worry about.

You will need to pull the head and make sure your valves are not bent or dammaged in any way.

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