[KnoxBreezer]

Posted this in the Mechanics forum, but it was suggested I post here also.

Original Thread (http://www.bikeforums.net/showthread.php?p=6459704&posted=1#post6459704)

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?

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[vik]

http://www.rohloff.de/typo3temp/pics/5147a9d222.jpg

Here is some info from the Surly Blog (http://www.surlybikes.com/spew19.html):

"Most single-speed hubs and internal-gear hubs, with 135mm O.L.D. spacing, will work on the Big Dummy, but a chain tensioner is required. Single-pulley tensioners, like the Surly Singleator, will only work in the “push-down” position due to the configuration of the chainstays. In some cases…when using a small cog or a worn drivetrain, there may not be enough chain wrap to prevent the chain from slipping over the teeth of the cog under high torque. A double-pulley tensioner (Pauls Melvin, Rohloff tensioner (http://www.rohloff.de/en/products/speedhub/chain_tensioner/index.html), or short-cage rear dérailleur locked into place with its high-gear limiting screw) may provide more chain wrap."

http://www.rohloff.de/uploads/pics/chaintensioner_01.jpg

I don't think you can use an eccentric BB on the Big Dummy as it was not designed to use one. Your simple options are to get a different chain tensioner as noted above and/or get a bigger rear sprocket on the IGH if it will accept one.

[AllenG]

That popping can cause your IGH damage.
The Rohloff chain tensioner is a good one and stopped the bounce induced slipping in my drivetrain all together. OnOne makes a good tensioner as well, called the Doofer. I have not used a Surly Singulator before but have had good results with both the On-one and Rohloff products.

And Vik is right, the bottom bracket shell on the BD is not large enough to accommodate an eccentric bottom bracket.

[KnoxBreezer]

Thanks for the tips! I have an older short cage RD I'm going to throw on there to act as a tensioner and see if it gives more chain wrap on the rear cog. Hopefully this will be a good fix for now and it will let me know if something like the Rohloff or the Paul Melvin will be suitable fixes.

[KrisPistofferson]

A little off topic, but I am just eaten up with a palpable sense of jealousy every time I read about you guys buying one of these. I absolutely love my LHT, and had a blast building it from the frame up. You guys get a cool bike, and have the pleasure of building it from scratch, I can barely take it. :)

When school's over I'm gonna go on a buying spree. :lol:

[vik]

A little off topic, but I am just eaten up with a palpable sense of jealousy every time I read about you guys buying one of these. I absolutely love my LHT, and had a blast building it from the frame up. You guys get a cool bike, and have the pleasure of building it from scratch, I can barely take it. :)

When school's over I'm gonna go on a buying spree. :lol:

http://bp3.blogger.com/_vUEhS0lU3eU/R7N9fFKWpwI/AAAAAAAAEZM/qjeCsvq61bA/s400/lht+porn.JPG

Yeah it will be a tough decision - do I ride the LHT or the Big Dummy...:eek::D;) Sorry to torment you....:rolleyes::)