Chain Comes Off Top Jockey Wheel - Suntour Blue Line RD
11-25-09, 02:36 PM
#1
50/50 Road/eBike Commuter
Thread Starter
Chain Comes Off Top Jockey Wheel - Suntour Blue Line RD
Hello,
I have a vintage Trek 613 from 1982 with a recently cropped-up problem: sometimes when riding, the chain comes off the top jockey wheel. The RD hanger was bent before this, but I adjusted it to be well within the specs that came with my Park DAG-2 alignment tool. I thought the problem may have been with the jockey wheel because it (and its dust caps) were fairly mangled. I bought a replacement from loosescrews.com, which has the same diameter (and # of teeth) but didn't quite fit with the dust caps in, apparently because the thickness of those caps is slightly too much. I also had to remove the original bushing and replace it with a short section of brass tubing because the mounting bolt (6mm) didn't fit in the original bushing. The fit is very close using the tubing - it spins very freely but has no noticable radial play. So I have the jockey wheel installed this way for now - with no dust caps. It has a very small amount of side-to-side play - couldn't be more than 1 mm. I applied grease to the mounting bolt. The fit between the wheel and the tubing is tight enough that the parts move together. The tubing rotates around the mounting bolt.
And the problem went away for about a month after this. I didn't want to run without the dust caps forever but at least I thought I knew that the problem was caused by the jockey wheel. But now the problem is back. It doesn't seem to happen when shifting. The jockey wheel is spinning freely. I have no problems with the shifting. The chainline looks nice and straight. The crank is a double, but I almost always keep it on the small ring. The rear wheel spins nice and freely. The chain is clean, with no measurable stretch, and lubricated. I'm at a loss. Anyone have any inkling as to what might be causing this problem? Anything I should check?
I was thinking that maybe the chain is too long, but if that were the case why didn't I have the problem before, considering I measure no stretch?
Cheers
Kevin
I have a vintage Trek 613 from 1982 with a recently cropped-up problem: sometimes when riding, the chain comes off the top jockey wheel. The RD hanger was bent before this, but I adjusted it to be well within the specs that came with my Park DAG-2 alignment tool. I thought the problem may have been with the jockey wheel because it (and its dust caps) were fairly mangled. I bought a replacement from loosescrews.com, which has the same diameter (and # of teeth) but didn't quite fit with the dust caps in, apparently because the thickness of those caps is slightly too much. I also had to remove the original bushing and replace it with a short section of brass tubing because the mounting bolt (6mm) didn't fit in the original bushing. The fit is very close using the tubing - it spins very freely but has no noticable radial play. So I have the jockey wheel installed this way for now - with no dust caps. It has a very small amount of side-to-side play - couldn't be more than 1 mm. I applied grease to the mounting bolt. The fit between the wheel and the tubing is tight enough that the parts move together. The tubing rotates around the mounting bolt.
And the problem went away for about a month after this. I didn't want to run without the dust caps forever but at least I thought I knew that the problem was caused by the jockey wheel. But now the problem is back. It doesn't seem to happen when shifting. The jockey wheel is spinning freely. I have no problems with the shifting. The chainline looks nice and straight. The crank is a double, but I almost always keep it on the small ring. The rear wheel spins nice and freely. The chain is clean, with no measurable stretch, and lubricated. I'm at a loss. Anyone have any inkling as to what might be causing this problem? Anything I should check?
I was thinking that maybe the chain is too long, but if that were the case why didn't I have the problem before, considering I measure no stretch?
Cheers
Kevin
Last edited by kmcrawford111; 11-25-09 at 02:43 PM.
11-26-09, 08:04 AM
#2
Senior Member
Well, you have hit upon most of the problem points. First of all, I would not run the upper pully wheel without the 2 dust covers. Try to find another SunTour used rear derailleur that you can utilize its upper pully wheel. If the chain continues to fall off the upper pulley wheel, you either have an alignment problem, as you have noted, or the upper pulley wheel has a lot of movement in it.
Suggestions (some of which you have already done). Make sure the rear derailleur frame droput is aligned correctly. Make sure the rear derailleur is perfectly vertical. Make sure the rear derailleur cage is not bent. Make sure that both pulley wheels are the same , so that your current upper one is not spaced closer than the bottom one. Check both rear derailleur cage plates-some obstruction ? I am still convinced that the problem is either lack of pulley dust caps , too much side to side movement, or incorrect spacing of the upper pulley wheel. There really is no other reason why the chain should fall off the upper pulley wheel. Good luck.
Suggestions (some of which you have already done). Make sure the rear derailleur frame droput is aligned correctly. Make sure the rear derailleur is perfectly vertical. Make sure the rear derailleur cage is not bent. Make sure that both pulley wheels are the same , so that your current upper one is not spaced closer than the bottom one. Check both rear derailleur cage plates-some obstruction ? I am still convinced that the problem is either lack of pulley dust caps , too much side to side movement, or incorrect spacing of the upper pulley wheel. There really is no other reason why the chain should fall off the upper pulley wheel. Good luck.
