fixing sprocket misalignment

[johnny q]

hi everyone - I have a skyhawk 80cc engine mounted on a kind of a junky
mountain bike frame. I am having problems getting the engine sprocket and rear sprocket to line up. Is there any good info here to show how to determine how much they are out ?

Also, is it possible to mount an engine on a frame and have it somehow twisted sideways a little bit ? I look at mine and it looks like that's whats happening. The engine is tight up against the frame, but it looks a little crooked. The mounts are tight though, so I don't understand how the engine could be tilted one way or another. It looks like the engine is not sitting level with respect to the seat downtube. If you look at it from the rear, it looks like the engine is off level 1 - 2 degrees. ????? I'll have to check it closer tomorrow and see if I can better describe what's going on.

It wants to throw the chain every time I try to ride it. what do you guys figure ?

thanks, JQ

 

[GearNut]

Most sit as though the front is tilted down a bit. The important thing is the carburetor. It needs to be as level as possible.
Sprocket alignment is the hardest part. some need a dished rear sprocket, dished side either in towards the spokes or out towards the chain stay. Others need a flat rear sprocket.
Some folks need to run the dished side out and use another set of curved sprocket mounting plates in between the outer rubber rag mount and sprocket to push it even further out.
Can you get any pictures sighting down the chain, back to front?

 

[azbill]

I ran a stack of 5 layers of rubber to clear a wide tire on my deviate !!!
every build is different !!!

 

[lordoflightaz]

I have been thinking about this a bit. Replacing the motor mounts seem to be the solution. I built my new bike with a rear mount. After consideration, I may go back and change that rear mount. The current setup has a plate that attaches to down tube with 2 muffler clamps (bracket looks very much like SBP shift kit mounting bracket) and is attached to the existing holes in the motor. If I make the bracket wider it would support horizontal slots rather than holes to secure the engine to the plate and be able to move the engine left or right so that the chain lines up. I would have to do the same thing the front motor mount as well, but that seems totally doable.

Realistically, it would be better if the motor sprocket could be adjusted, but I don't see that happening.