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Monday, November 23, 2009

DIY Roller Chain Tensioner

I feel heavy! I have not been riding trials for 3 weeks already. Heavy rain everyday, broken rear wheel spokes on the 20" and a faulty derailleur on the 26" really put a damper on things!

The 20" Monty 221PR had been good to me. I had been training and riding it almost everyday. The problem was that one of the spoke broke. I got it repaired... and before I knew it, more spokes broke. From what I understand from a friend, when 1 spoke breaks, more will break soon after and that it is best to change all the spokes. I am still deciding what to do next.

In the meantime, I started riding my Echo 26". It went well for a while, until one day, when I pedal up, the roller chain broke and shot behind me into the pallet. Luckily, I managed to recovered without any injury... phew! Sure scared the heck out of me!

In the end, I found out that the cause for the roller chain to break was due to the derailleur casing. Apparently, the casing was out of alignment and the roller chain was rubbing against the sprocket casing. My guess was that the roller chain snapped when it was caught by the misaligned sprocket casing.

Anyway, I managed to re-attach and oiled the roller chain. But... I just could not bring myself to trust the roller chain again. I had lost almost all confidence in the chain and the derailleur.

And so, I had not been riding trials for the past 3 weeks. Then I remembered what a friend (Wong Xu) told me. He said that I could make my own roller chain tensioner. The basic idea was to use a V-brake arm coupled together with a roller chain sprocket from a derailleur to make a chain tensioner. He did not go into the details.

And so, last weekend, I decided to try make a chain tensioner out of a V-brake arm and an old derailleur sprocket.

I spent about USD2.50 to purchase one side of a V-brake arm. I removed the brake pad and spring from the V-brake as I only needed the arm bracket... :-)

From my Echo bike, I removed the roller chain and took apart the old derailleur. The only thing I wanted from the derailleur was the hanger and the sprocket. My plan was that the sprocket will be attached to the V-brake arm, and the V-brake arm will be attached to the hanger and then mounted on the bike.

I removed the sprocket from the old derailleur.

I needed to find a stainless steel nut that will fit the screw holding the sprocket. Had to visit several hardware shop before I found what I wanted.

I fitted the sprocket to the V-brake arm just to get a feel to see if I was going in the right direction.

After half a day of trial and error, I managed to come up with 2 ways of mounting the sprocket on the V-brake arm. Both did not work very well because the screw on the hanger was not long enough to mount correctly.

Version 1.0 of the Chain Tensioner

I did not like the way I mounted the sprocket. It was gripping the roller chain in a manner that did not inspire confidence with me... LOL. Also, the V-brake arm was mounted on the inner side of the hanger with a hanger screw that was too short, which did not allow me to tighten it as securely as I wanted.

Video of Version 1

Version 2.0 of the Chain Tensioner.

This second version was much better. I reversed the V-brake arm then used nuts and spacers to extend the reach of the sprocket to the chain. The sprocket was gripping the chain nicely. Problem was still at the hanger. I could not find a screw long enough to fully attach the arm onto the hanger securely.

Video of Version 2 in action.

After test riding with Version two for while, the chain became slacked. Tightening the screw on the hanger did not help either. I guess it is back to the drawing board.

I will probably have to think of a way to use a spring to provide added tension and also to find a longer screw that will fit the hanger!!!

Arrrgh!!! No bike to ride!!!

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