Motor chain comes off catches and snaps

colonelkrs

New Member
Jan 10, 2013
23
0
1
Oakland CA
I broke a rim and had to replace it. I found an old rim in a friend's back yard but now my chain keeps jumping off catches and snaps. I noticed the rim is missing a spoke. How do I get my bike to work? Is it just the rim causing the problem or could it be my 36t sprocket?
 

crassius

Well-Known Member
Sep 30, 2012
4,032
155
63
USA
a pic would help, but my first guess would be that you need to get your tensioner more closely aligned with rear sprocket
 

colonelkrs

New Member
Jan 10, 2013
23
0
1
Oakland CA
No tensioner on this bike. It's a stretch Dyno cruiser. Had this frame 4 years and 4 motor kits. Can't really fit a tensioner either.
 

colonelkrs

New Member
Jan 10, 2013
23
0
1
Oakland CA
When I took the bike my rear sprocket turns inward at one point and doesn't line up with the chain. Then it gets tight and comes off or snaps bc the teeth aren't in the slots for the chain.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
155
63
USA
sounds like when you moved sprocket to new rim, it no longer is aligned properly - getting tight, then loose means up/down alignment is off, wobbling side to side means sprocket isn't on straight - just offset all around usually means hub is thicker/thinner than old one and *might* be fixable by adding/removing spacers between axle and frame
 

Chaz

Well-Known Member
Jun 3, 2012
1,004
69
48
Vancouver, British Columbia
All of the above and you do need to replace the missing spoke. You won't be able to true your wheel and rely on it with a spoke missing. First sort out the wheel and then align the sprocket. Check out Sheldon Brown's site for details about truing the wheel.
 
Nov 27, 2013
143
4
18
earth
www.Frankenbikes.com
i think Chaz is right, it will/may always be out of alignment with(out) the missing spoke. Too bad the rag joint (i'm assuming} is all mounted up, that spoke would be EZ to replace before the sprocket was mounted. If it is some other kind of mount perhaps the spoke can be replaced in situ.
Crassius too is correct, and if it is a rag joint, the bolts on one side may be tighter than the other, making the plane of the sprocket tilted in relation to the plane of the rim. That popping sound, BTW, will likely soon be followed by a chain link being pushed apart.

In my later builds i have been loosening the spokes a little before i install the rag joint. It allows me to move the spokes out of the way for the bolts, and i ususally wind up having to true the rim anyway after cranking down the sprocket joint etc. That sprocket and joint puts a lot of new, weird pressure on the spokes.

I made a tool to help with the "concentric" aspect of mounting. It does not prevent the sprocket from being off center but is more like a gauge or measuring tool. If you lift it out and it binds, the sprocket is not centered. But this allows me to concentrate on the "tipping" aspect which i both eyeball and use a block clamped to the chainstay to "measure"