Hi friends, I have atv with CN250 honda helix clone engine, and I had nothing but problems with it so far.

I rebuild the engine last week, and get back the engine on atv frame ,connected everything and it started immediately, so I went for a test drive for a few kilometers and got back.
Week after that I tried to start atv and it would not start, with choke on or without , put some fuel into spark hole and tried but nothing.

So I started disasembling it again and found out that woodruff key that holds magneto on place is broken and it moved on shaft for about 45 degrees, so it was out of timing.

My question now is can I fit new woodruff key and is this useable or not regarding the crankshaft and magneto. They did get some damage both crankshaft and magneto and I am not sure can I reuse those parts again??




What could cause this issues, did my engine got overheated ??

I also noticed a lot of black deposits on piston, but they look like oil and carbon deposits,and it was only a few kilometers run, Could it be the oil leaking through the valve seals in to the combustion chamber?

 

The reason the timing slipped is you didn't tighten the flywheel enough. It is a tricky one as, too tight and they are extremely difficult to get off again, even with the correct puller, not tight enough and that happens. That is one nut that I always set to the correct torque, if I can find what that is. Put valve grinding paste on the taper, refit flywheel without the key, turn the flywheel backwards and forwards with light pressure on flywheel, whilst stopping the crank from moving, just like grinding a valve in. Once both tapers are that uniform grey all the way round when you clean the paste off, you can fit a new key and re-assemble, using a torque wrench.