Top Dead Center and timing

[berniebigbore]

Hi.  I have a 49cc Tao Tao that is brand new.  I just put a 47mm bbk in it, with the stock head.  Since the bbk install I am dying trying to get my cam lined up at top dead center.  It is always one tooth off.  I adjust a tooth one direction and the timing mark on the sprocket goes below the head. I adjust it one tooth the other direction and its above the head.  The marks on the fly wheel feel unreliable.  I have gone back down to the cylinder with the piston visibly at top dead center and the flywheel is an inch after the T mark.  If i try to line up the flywheel, the piston moves and then the flywheel and piston fall back to a resting position with the flywheel an inch after the T and the piston at TDC.  When I get the head on and get to the cam, nothing has moved, and I am still one tooth off.... I have all nuts and bolts torqued to spec.... Please help me I don't want to seal it up with bad timing and bend a valve.

[berniebigbore]

Crap! I think I should have started this thread in 4 stroke performance, not troubleshooting. Sorry. Not my first 4 stroke but it is my first forum.

[pinkscoot]

Maybe one of the 4 stroke guys will help you.

[gsx600racer]

You could try this.

[berniebigbore]

Genius! Thank you! This is why I love this forum. Everything that I have learned about my mopeds, I have learned from this forum and these videos. Smart, educational and reliable and really makes wrenching fun and easy. I'm applying the degree wheel tomorrow.
Thanks again

[90GTVert]

I have had one of my flywheels for a 139QMB be over 20 degrees off. Found that with a degree wheel. It ran slow no matter what I did to it, before that was found. Bought a new flywheel and it lined up with TDC and all was well again. You may be experiencing something similar, though maybe not so far off unless you've noticed uncommonly low performance. The degree wheel will tell you. If the flywheel is not aligned properly, it's not just cam timing that it screws up though. It affects ignition timing too. You can remove the woodruff key and carefully clock the flywheel and the nut pressing it onto the taper should hold it, but it's a whole lot easier to replace the flywheel and not have to deal with that every time you work on it.

Fair warning, when you start messing with cam timing, you must be careful to make sure the valves aren't hitting the piston. The simple check is to make sure you rotate the engine over before it ever starts. More thorough checks are shown in vids below, but most won't bother.

[FrankenMech]

Offset timing keys can be purchased for some engines.