Chain Tensioner Idler related accidents

[happycheapskate]

I have figured out how the infamous chain tensioners could cause the accident described some on this board (going into the spokes and wrecking the wheel).

The chain tensioner/idler may rotate on the chainstay if it is not welded or pinned with a set screw, esp on bikes with narrow chainstays such as a ten speed road bicycle.

Also, if the torque of the motor (esp at low engine speeds, such as starting) moves the axle forward a little, it can skip a tooth on the driver cog and jam in the driver cog cover (where the little clutch arm is). This locks the chian while the wheel is turning, pulling hard on the idler, and possibly dislodging the wheel axle or pulling the idler hard, which can drive it into the wheel.


I really thing the solution is to use a chain tensioner if possible, the kind that pulls the axle with a bolt welded to a washer.

I like the auto tensioners that mount to the seat tubes, but I cannot find these in the catalogs I have checked so far. Please respond if you have one and tell where you got it and how well it is working in service.

[Stan4d]

I am on my second build....I got a 7 speed and am thinking that the tensioner will not be neccesarry. The pedal chain has a tensioner that keeps it tight with plenty of adjustment. Going to set the motor chain tight and adjust pedal side.

[happycheapskate]

If you are using a quick release skewer, you might want to weld "lawyer tabs" on the dropouts, esp the motor side. This will prevent the axle from being able to move forward unless the QR is really loose.

[Stan4d]

thanks for the heads up. I avoid quick release altogether though. Something about having something that I want to stay put being able to come off quickly just does not seem right.

[happycheapskate]

Quick release skewers work by cam leverage, and can hold just as tightly as axle nuts. The problem is the axle is weaker and subject to bending under heavy stress (clydsedale riders, jumping, motors).

If you can find castellated nuts for your axle, you can very easily get a tight grip (they are nuts with attached washers, allowing the nut to rotate while the washer is still against the frame dropout. You can also use knurled washers if you can find them, for the same purpose. Smooth washers will move.

[Lazieboy]

I got my pant leg caught in mine just a while ago. No accident i was lucky. scared me.

[happycheapskate]

Good tip. I ride in work pants most days because I can with the motor now, and I have to remember to tuck the leg in a sock, or use tape, a strap, a piece of rope, etc.

You can get a couple toe-clip straps for next to nothing maybe free at big bike shops. Look in the bargain bin and garbage dumpster.

Velcro straps also work great and can be had cheaply.

[happycheapskate]

I got these ORigin 8 chain tensioners today (pair) for $10 at Don Johles Bike World in Garland TX. I am looking to find them online for you.

Here is the mfg website: http://www.origin-8.com/product_deta...ter&cl1=CHAINS

The product photo: http://www.jbimporters.com/web/images/new_400/16216.jpg


I bought this for use on a beach bike with horizontal dropouts (Axle exits forward). I expect to grind flats on the backs of the dropouts for a more stable surface. This is for 3/8" axles, and comes with Nylock nuts!

[happycheapskate]

#### They don't work on bikes with forward facing dropouts. The end cap just keeps turning and the screw bends until they are wasted.

For a BMX or something though, they were great, esp for $10.

I expect I'm going to have to get another of the Death Idlers, and weld one on each side, and weld tabs on the dropouts, so I can finally ride this sucker without having to stop all the time and move the axle back again.

Forward dropouts SUCK unless you have a nice road bicycle with derailleur.

[happycheapskate]

For whoever mentioned Star Washers in another thread, thanks.

I found them at Home Depot for 35ct/ pair. I took off the tensioners I was abusing, and installed on each side, 1 star washer, 1 flat washer, 1 more star washer, and the standard wide bottom axle nut. This let me put some major tension on the dropout without stripping the thread, and seems to be semi-permanent. We'll see tomorrow if it moves or stays tight. I"m betting on it not moving for a long time.


I really believe that the chain-tensioner accidents are caused by axles moving forward, slackening the chain which derails, and also rag-joint mounted cogs which move out of round, same result.

If you can find track nuts, they might be an even better choice (made for this problem)

http://sheldonbrown.com/harris/fixed-hubs.html