110cc - Wierd TDC Issue

[Pitbike Tuner]

Trying to get my engine to top dead center and have the 2 covers off. Issue is when turning counterclockwise and looking thru the top hole for the "t", whenever the engine gets to it it turns quickly past it and I cant get it to hold there. I had the spark plug out as its threads are stripped and I'm going to change the head to fix that issue, but even putting the sparkplug in it does the same.

[Crossbar]

At TDC both valves should be closed and there should be no spring pressure on the cam. If you're sure it's at TDC and not in between then could it have jumped timing or valve adjustment too tight? Did the engine run ok before? Find a way to lock it down at TDC and check the valve adjustment.

[TominMO]

Use a wrench or breaker bar to turn it, not something with a ratchet. That gives you a lot more control.

[Pitbike Tuner]

Originally Posted by Crossbar

At TDC both valves should be closed and there should be no spring pressure on the cam. If you're sure it's at TDC and not in between then could it have jumped timing or valve adjustment too tight? Did the engine run ok before? Find a way to lock it down at TDC and check the valve adjustment.

Not sure how it ran before, got it from someone who said it wasn't running and found out the spark plug threads were stripped. It turned over fine when trying to start, and came with a new complete head so think the guy new of the issue. The engine turns without much resistance at all, and then when it gets just to TDC it spins quickly about a half turn.


So to check the valve adjustment just pull the top and bottom caps after getting it at TDC correct?

[cheesy]

Pull the caps first. Set crank at TDC. Both valves should be closed as Crossbar said. If one valve is open, rotate the crank one revolution and line up with timing marks again for TDC. Both valves should then be closed. If still not, the engine has jumped time.

[krat]

Questions;
Are you installing the new head? If so you set TDC on the flywheel and install the new head and adjust the valves to match. That should also take care of any timing problem that might have existed. You will line up the cam and lifters to the new head with the timing chain in the proper position.

It also makes the spark plug issue a moot point.

Otherwise, why would you try to adjust the valves on a head that was trashed?

[Pitbike Tuner]

Originally Posted by krat

Questions;
Are you installing the new head? If so you set TDC on the flywheel and install the new head and adjust the valves to match. That should also take care of any timing problem that might have existed. You will line up the cam and lifters to the new head with the timing chain in the proper position.

It also makes the spark plug issue a moot point.

Otherwise, why would you try to adjust the valves on a head that was trashed?

Yes, installing the new head.



I'm just wondering if the engine has an internal issue as it seems way to easy to spin, no resistance pretty much, and quickly went past TDC when turning it with the wrench and it hit close to that point.