Bicycle Mechanics - Surly Big Dummy, Nexus 8 speed w/ singulator - chain slippage problem?

Hello all,

Shop recently built up a Surly Big Dummy for me. I moved over most of the drive train parts from my Breezer Uptown 8, which previously had the standard xtracycle kit attached. Drive train is internal hub red band nexus 8 speed with single 38t chainring.

When this was setup on the Breezer/xtracycle combo the chain was tensioned using the forward facing horizontal dropouts on the breezer frame, moving the xtracycle free-radical attachment back in the dropouts to tension the chain. However, the Big Dummy frame has standard vertical drop outs, so to use the same system some sort of chain tensioner was needed. We decided to use the surly singulator to accomplish this.

With this singulator setup on the Big Dummy I'm experiencing chain popping/slippage when putting power to the rear wheel. Under normal pedal it's OK, but as soon as I stand on the pedals or put much power (usually up hills) the chain starts popping. This happens frequently, with no extra load on the bike, and I'm concerned that with the singulator there isn't enough chain wrapping around the cog to ensure a complete connection. This is complicated by the hub's cable/shifter arm posing an obstruction to the singulator. I've noticed that some use the singulator in a "push up" mode opposed to the standard "push down" mode but the configuration of the Big Dummy's chain stays prevents this.

With the old setup on the Breezer frame I never experienced this problem, leading me to believe this is a result of not having the chain in contact with enough teeth due to the use of the singulator. I haven't found any other feedback, so any suggestions would be greatly appreciated. Maybe the singulator isn't the cure to my problem... should we consider an eccentric bottom bracket like those used on single speed mountain bikes? Would this provide enough movement to properly tension the chain (long, long chain) to use this internal hub on the Big Dummy?

Have you checked your chainline? The popping you are hearing may be the chain trying to jump off the chainring or cog, not the singulator.

One time I had this same problem with my redband Nexus-8. Fine when I was on the saddle, slipping when I stood up. My chain was too slack. You have a lot of chain on something like a Big Dummy. I'd take a look at that.

I thought that the Surly Singleator didn't have enough spring tension to handle the extra chain on my Xtracycle. I switched to the Soulcraft Convert. It doesn't rely on a spring to take up slack in the chain. Really solved the problem.

http://www.soulcraftbikes.com/convert.asp

It may be your cog is worn out.

Make sure you've got the Nexus dialed in (the little yellow marker deal). I had a similar problem and it was actually that.

I thought that the Surly Singleator didn't have enough spring tension to handle the extra chain on my Xtracycle. I switched to the Soulcraft Convert. It doesn't rely on a spring to take up slack in the chain. Really solved the problem.

Good point. A quick check for the OP would be a ghost ring to take up the slack. Would let him test the theory real quick.

Is the singleator pulling the chain up, or pushing down. Make sure it's pulling up as that will wrap the chain around the rear cog.

Haven't gotten around to completely specifying the build on my future BD, but the Paul Melvin tensioner looks like it might be a better approach with it's double cogs... comments?

Thanks for all the input. I am pretty sure it's not a chainline issue, a visual inspection seems to show it running pretty true. There is a LOT of chain, so I would assume the chainline wouldn't have to be completely spot on. I'm also reasonably sure the cog is not worn, this cog only has maybe 1200 miles on it and the drivetrain was kept very clean. The nexus is lined up properly, little yellow lines mating up when in "4."

This slippage/popping problem never occurred when the same hub/cog was used on the breezer/xtracycle combo with similar length chain. The only difference is with how the chain is tensioned (using the horz dropouts before, and now the surly singulator), and a different front chainring (salsa).

I'm beginning to think the singulator may not have enough spring to tension properly, as mentioned above. I don't think I can use it in "push up" mode due to the configuration of the dropouts/chainstays and the shifter arm on the hub posing an obstacle, but I'll certainly give it a try again. The soulcraft or the melvin may also be better solutions for this application, thanks for the recommendations!

Otherwise, you might try using a short cage rear derailleur as a tensioner.

Also, you might want to check in the Utility Cycling forum. The Big Dummies hang out there. :)

I have some experience with this. I had a single speed mountain bike with a singulator style tensioner and it would pop when climbing. You're right to guess it's the tensioner. Now, I ride an xtracycle with a rohloff hub and use the supplied tensioner. ZERO problems. This tensioner is light years ahead of anything you'll come across. Tension is so tight and machined so well. Expensive, but it will fix your problem.