Re: 20 toothe sprocket?
Chain/sprocket alignment is critical. So is the tension.
You'll have to concentrate on getting the rear sprocket aligned perfectly with the engine drive sprocket. Very little lateral misalignment is allowed. Some kit supplied sprockets are flat where others are 'dished'. That means the teeth are offset to one side. If your sprocket is flat you'll have to determine which way it needs to go, right or left, to get the chain path straight. Sometimes that means shimming the rear wheel off to one side or the other and/or the sprocket. If your sprocket is the dished type you can flip it to move the chain in or out.
There are other methods but keep in mind that clearance with other parts, such as the bike frame and rear tire, is also important.
The rear sprocket also MUST be centered on the hub and have no wobbles either vertically or horizontally. It must spin true.
Are you using a chain tensioner? If not, the alignment is even more critical. If you have a tensioner it can help with slight side to side misalignment because it can assist in 'guiding' the chain onto the rear sprocket, if installed correctly.
Keep us informed and ask if you need more help.
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Last edited by 2door; 12-04-2011 at 10:17 PM.