Chain Tensioner Falling Into Spokes - Mystery Solved

moronic_kaos

moronic_kaos

New Member
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:

  1. 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.
  2. 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.
  3. 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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Moronic,
First of all you need to assure that the rear sprocket is EXACTLY centered on the hub. Even a smidge off and you're going to have continuing chain problems.
Second. Secure the tensioner bracket to the bike frame after assuring that the alignment is right on. That usually requires a slight twist in the bracket to get the tensioner wheel to align with the chain due to the taper of the chain stay as opposed to the wheel.
I'm not sure about your gasket material idea. That seems like a temporary fix to me. The tensioner bracket must be affixed to the bike frame, chain stay, in such a way as to assure that it cannot rotate inward. Just my opinion, but one shared by many builders.
Tom
 
Since the tensioner only mounts to the chain stay (one spot), there is no way to ensure it can't rotate in-ward. With the right amount of force it will always be able to fall. The only way to fix it is to make sure it doesn't get too much force and to give it a better grip on the chainstay (traction).

Secondly, a lot of builders don't have access to the right tools and don't have the patience to pull the sprocket on and off a billion times before getting it perfect, especially since the threading on the bolts strips so easily. You just have to make what you've got work. We don't all have access to a full-blown tool set or indoor work area.

Do agree though, 9/10 of the time the tension has to be twisted a bit.
 
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Or as I have always said...3/4" of free play at the tightest point.

You don't have to take the sprocket off a billion times, just loosen it a bit and tap it with a rubber mallet until it's pretty straight.
 
I, like a few others on the forum,run a small self tapping screw through the bracket into the chain stay.Mine has been like that for around 8000 miles or so,without any problems.
 
dvddtz said:
I, like a few others on the forum,run a small self tapping screw through the bracket into the chain stay.Mine has been like that for around 8000 miles or so,without any problems.
Click to expand...
This method has worked for many but I hesitated to mention it because it always seems to ignite a fire storm of criticism. Some firmly believe that drilling into the chain stay will weaken it. I firmly disagree with that theory. I've used a 10-32 bolt through the tensioner bracket and bike frame and it has never hinted at the catastrophic failures predicted by some. It will however keep the bracket from moving and that in itself will prevent a major problem that so many have had when the tensioner bracket rotates inward and contacts the spokes. I've yet to see one conclusive photo or any evidence of frame failure caused by drilling into the chain stay (frame). Admittedly I have abandoned the clamp on style of tensioner bracket and have fabricated welded on, custom made tensioner wheel brackets. I realize that everyone does not have access to special tools and equipment required for this type of modification and that is why I suggest using the drill/bolt method. Clamping with the kit supplied hardware is an invitation to trouble in the way of ruined rear wheels/spokes and the potential for injury if the tensioner gets into the spokes at speed.
Tom
 

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steel set pins at Lowes are cheap...drill a small hole thru the bracket and frame and pound it in so it sticks out both sides...as far as gasket material????I use GOOP...its amazing stuff...good luck...Dennis
 
After having the tensioner come loose on me due to stripped bolts I'd say ditching the original nuts and bolts on the tensioner with quality stuff is a must as well. That and I always check it with a kick before I go for a ride. I'm still a noob but that's my best noob advice :)
 
As long as you drill the hole in the side of the chainstay, it does not weaken it along the loaded axis. The bottom of the tube is under the most load, then the top, the outside,and the inside. Have little load in comparison.
 
When ever I build a bike that uses the chain tensioner, I always put two small sheet metal screws through the tesioner & into the frame. I've never had a problem with the frame breaking, or the tensioner moving!
 
comrade...did you get your bike up and running?...hope so...at Lowes you can get those small steel set pins that you need...drill the hole smaller than the pin and hit it in with a ball peen hammer...you live in a beautiful area...was stationed there when i was in the Marine Reserves...hope you are riding and enjoying the area...Dennis
 
Bike is almost running, had to get the wheel respoked after a 1/10 mile ride, grumble. but I could have it going by the end of the week. When computers stop hating me I'll add some pic's also got a great tire set up
 
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