It's a really simple concept, but fixing it can be a pain in the rear. The tensioner hits the wheel because it has no other place to go. Why?
When you've got your bike assembled, move the wheel about 90 to 180 degrees and re-check the chain tension. Odds are, it's a little tighter or looser than it was before. It's because the sprocket is off-center. No, it may not wobble, but that doesn't exactly mean it's centered to the hub. When the sprocket is off-set like that, you get an irregularity in your chain tension. What's that go to do with anything?
Think about it. Your chain is constantly going from finely adjusted to way to tight. This creates a "pounding"-like effect on the tensioner, as if it's getting beat with a hammer. With enough pounding, it will eventually fall into the spokes (either that or the chain snaps). If you don't believe me, pound it with a hammer a few times.
So how to fix it? Three things you can do:
When you've got your bike assembled, move the wheel about 90 to 180 degrees and re-check the chain tension. Odds are, it's a little tighter or looser than it was before. It's because the sprocket is off-center. No, it may not wobble, but that doesn't exactly mean it's centered to the hub. When the sprocket is off-set like that, you get an irregularity in your chain tension. What's that go to do with anything?
Think about it. Your chain is constantly going from finely adjusted to way to tight. This creates a "pounding"-like effect on the tensioner, as if it's getting beat with a hammer. With enough pounding, it will eventually fall into the spokes (either that or the chain snaps). If you don't believe me, pound it with a hammer a few times.
So how to fix it? Three things you can do:
- Most Important Tip: Tighten the tensioner when the wheel rotation = the chain being the most tightest. That way it goes from perfect tension to a little bit loose. It will function with a reasonable amount of looseness.
- You could try & re-center the sprocket again to get a closer match. It will really never be perfect though unless you have some sort of stand to measure it with, so even then follow #1.
- Wrap the part of the frame where the tensioner mounts with a spongy-like gasket paper to help the tensioner grip the frame (same effect as the rubber/plastic inside of a lock nut) Too thick = the tensioner wobbling, Too paper-like & it wont grip. Should be the same consistency as the gasket material used for the cylinder base & intake gaskets) This will prevent the tensioner from slipping over time due to vibrations and a small amount of chain pounding.
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