I would like to add two chain tensioners

[vavavroom]

That's crazy you say and you may well be right. Let me explain. My bike has a Nexus 8 geared hub and there's only a cog just like on a fixie. Chain tension is adjusted by loosening both axle nuts and by pulling back on the wheel while also making sure the wheel is centered in the rear track fork. This is a bit fiddly and for convenience's sake, I would like to install chain tensioners on both sides.

Something like this? Because of the white locking washer required by the geared hub this tensioner design won't fit.

 

[MRC01]

That's crazy you say and you may well be right. Let me explain. My bike has a Nexus 8 geared hub and there's only a cog just like on a fixie. Chain tension is adjusted by loosening both axle nuts and by pulling back on the wheel while also making sure the wheel is centered in the rear track fork. This is a bit fiddly and for convenience's sake, I would like to install chain tensioners on both sides.
...

I have a bike with a 2-speed internally geared kickback shift hub. Only 2 speeds instead of 8, but the principle is the same. As you may already know, the axle must be secured against rotating since the planetary gears inside these hubs exert a reverse torque around the axle (unlike a normal hub, which does not). That's why the axle has opposite sides shaved flat to fit in a lockring washer to prevent rotation. So (master of the obvious aside) you've got to work within these constraints.

I find the easiest way to set the chain tension is to position & tighten the axle one side at a time. One side tight, the other side loose, position the loose side. Then tighten the loose side, loosen the other side, position it and tighten it. Done this way the process is less fiddly and quicker. So I haven't found a need for the kind of tensioner bolts you show, which are often used on motorcycles.

Also remember the chain tension is never even all the way around; as you spin the pedals the chain always has a loose point and a tight point. This is because the chainrings/sprockets are never perfectly centered. So when adjusting, move the pedals to find the tight position of the chain, and set the tension at that position so it's not completely tight but still has just a bit of slack. The loose position will be even looser and that's OK.

 

[vavavroom]

Less fiddly would be nice. Maybe I can circumvent the keyed washer by attaching a tensioner on the inside. The prong on the keyed anti-rotation washer protrudes only about halfway into the slot.

 

[NYEngineer]

Your pics aren't coming through on my computer so I don't know what parts you are considering. Is one of them the Surly Singleator? That works pretty well. I just reread your post. Now I see what you mean.
One thing I do when building bikes with Alfine hubs or single speed is use a single speed chain with a half link. Sometimes it's the only way to get the tension right. I think KMC makes it.

 

[MRC01]

... One thing I do when building bikes with Alfine hubs or single speed is use a single speed chain with a half link. Sometimes it's the only way to get the tension right. I think KMC makes it.

Bike frames made for geared hubs should have horizontal rear dropouts so you can set chain tension. That should obviate the need for half link chains. Are you converting bikes made for derailleurs (vertical dropouts)? Or are you using the half-link chain with horizontal dropouts, in order to get more precise rear wheel position / wheelbase?

 

[NYEngineer]

Yes. That is a difference I failed to mention. I usually do this on Surly bikes which have horizontal dropouts.

 

[vavavroom]

The problem with adding tensioners is that I can't fit them on the outside because the locking washer will interfere with the tensioner. My only chance is to fit the tensioners on the inside which may be impossible due to the internal width of the fork, unless the tensioners are very-thin. 35 years ago I had two tensioners on my BMX bike. Worked like a charm for setting not only chain tension but also for centering the wheel.

 

[vavavroom]

Your pics aren't coming through on my computer so I don't know what parts you are considering. Is one of them the Surly Singleator? That works pretty well. I just reread your post. Now I see what you mean.
One thing I do when building bikes with Alfine hubs or single speed is use a single speed chain with a half link. Sometimes it's the only way to get the tension right. I think KMC makes it.

I can get the tension right just fine. Centering the wheel is the trickier part. Borderline OCD is the problem.

 

[MRC01]

I can get the tension right just fine. Centering the wheel is the trickier part. Borderline OCD is the problem.

The one-side-at-a-time approach mentioned above makes this simpler and easier.

 

[vavavroom]

The one-side-at-a-time approach mentioned above makes this simpler and easier.

That's what I've been doing all along and I'm still not thrilled. More power to you.

 

[anga]

Will it help if you rotate the non-turn washer by 180°? The projection will face the rear and out of the way.
Once you get the position that works for you, maje marks on tge dropout to guide you the next time.

Of course you can use two tensioners.

 

[Number_35]

@vavavroom, this doesn't help you, but Jr's winter bike is a single-speed, and tensioning is easy due to the design. The frame is drilled and tapped to accommodate an M5 (if I recall correctly) cap-head screw (i.e. recessed hex for an Allen key) on each side.

I adjust these until the wheel is straight and the chain tension is correct, and then tighten the larger bolts on the side to provide the holding force.

Winter riding takes a terrible toll on a bike. I use lots of anti-seize on the tensioning bolts, and have to replace them periodically.

 

[vavavroom]

Something like this should be a standard feature. I have not yet found a solution for my bike. I don't have enough room to fit a conventional; chain tensioner because of the locking washers that are part of the Shimano Nexus hub.

 

[AZjeff]

Imagine if you took the stamped "bracket" off and un-bent one of the sides back almost straight. It might be enough to catch the end of the horizontal dropout and let you adjust the axle as intended. If that wouldn't work do you have the ability to fab a little piece out of maybe 1"x1" angle steel that would have enough reach to get the dropout? Actually wider C channel would function just like these with a little fab work. A fender washer might have enough width if you have a way to put 90 bends in it and it already has a hole. The eyelet bolt is the important part, the bracket is easy.

 

[SC Maintenance]

Something like this: https://www.sheldonbrown.com/singlespeed.html

 

[AZjeff]

@SC Maintenance , he has horizontal dropouts, might as well use them if he can. Never liked that style of tensioner that reduces chain wrap on the gear. When we were building SS bikes BITD we'd use the tensioner that bolted to the derailleur hanger and pushed the chain up.

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[SC Maintenance]

@SC Maintenance , he has horizontal dropouts, might as well use them if he can. Never liked that style of tensioner that reduces chain wrap on the gear.

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I agree I wouldn't want one either, but that was the OP's entire quest - he didn't want to rely on the horizontal drop outs to tighten his chain and get the wheel aligned.

 

[AZjeff]

Crude quickie with a large fender washer and the vise, not right but I could see it working if the left bend was closer to the hole.

 

[vavavroom]

Crude quickie with a large fender washer and the vise, not right but I could see it working if the left bend was closer to the hole.

View attachment 128645

Are you covering an eye for the axle with your thumb? How will this not interfere with the locking washer that prevents the Nexus axle from spinning? If the axles were longer a tensioner could be fitted on the outside of the locking washer, but the axle is just long enough as is.

A combined locking washer with an integrated tensioner could be machined. I could ask one of the shop guys at work to whip this up for me.