Safety Chain Tensioner Idler related accidents

Discussion in 'Travelling, Commuting & Safety' started by happycheapskate, Apr 2, 2010.

  1. happycheapskate

    happycheapskate Active Member

    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.

  2. Stan4d

    Stan4d New Member

    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.
  3. happycheapskate

    happycheapskate Active Member

    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.
  4. Stan4d

    Stan4d New Member

    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.
  5. happycheapskate

    happycheapskate Active Member

    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.
  6. Lazieboy

    Lazieboy Member

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

    happycheapskate Active Member

    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.
  8. happycheapskate

    happycheapskate Active Member

    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:

    The product photo:


    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!:tt1:
  9. happycheapskate

    happycheapskate Active Member

    More drastic measures needed.

    #### 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.
  10. happycheapskate

    happycheapskate Active Member

    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)[​IMG]
    Last edited: Apr 6, 2010
  11. happycheapskate

    happycheapskate Active Member

    The star nut-washer-star nut-axle nut combo worked good. Either it only moved once, or the new chain "stretched" just a little during the first couple rides (likely).

    I just bought this KORE Chain Reactor Chain tensioner at /Contact_Us.php for $26 plus $10 shipping including shipping for 2 KMC Z chains! [​IMG]

    Its a click-n-mortar store in Colorado, the mountain bike state.
    Last edited: Apr 8, 2010
  12. happycheapskate

    happycheapskate Active Member

    Maybe now we're getting somewhere. I don't know why Grubee can't just sell something like this. I know somewhere you can buy seat tube mounted spring tension rollers similar to this, but I haven't found them yet.[​IMG]

    This looks like it will finally be my solution for optimum chain tension.

    I ordered 6mmx1.00x75mm machine screws (threaded all the way down to head) from Fastenal Inc at about $1.50/each.

    I am going to use one screw in the top right corner, to replace the long screw (where chain cover mounts with lock nut). With this long screw, I can tighten with locktite, then add 1 washer, a plastic bushing, the roller arm mounted over the bushing, another washer, a nut and a locknut. The spring will have to be modified a little to fit a small drilled hole in the driver gear case so it can pull down on the arm. I'll take more pictures next week after assembly, and will have a few extra screws for buddies.

    Notes: I have a Madwagon beach bike with the fat tubes. I used the stock mount on the seat tube with no shims. The roller arm will be close but not touching the seat tube. If you have thin tubes (chinese 10 speed, old style mountain bike) you should have a good clearance, otherwise you might have to file the metal on the arm (where the screw goes through the tube), or on the back of the gear case a little.

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    Last edited: Apr 14, 2010
  13. happycheapskate

    happycheapskate Active Member

    The KORE chain reactor does not work with MB's. (It can work well on the pedal side for a multispeed bike, to prevent chain suck or chain slap, but does not work on the motor side).
    I have a brand new one with packaging and instructions for sale. I put it on the frame but did not tighten any nuts or scratch it. It cannot work with the high mounted motor's chain line (does not go over the chainstay like a regular pedal chain).

    It would be in the spokes. It can't fit.

    The product looks nice though, and with some Loctite, should be a safe and durable product as intended, for a multispeed bike. Does not work for converting a singlespeed either! (some might say it does, but the package says its not).
  14. happycheapskate

    happycheapskate Active Member

    Please excuse me. Castellated nuts are for automotive use, or some motor applications. They have cuts on them like the walls of a fort in a crude drawing, and use cotter pins to lock them.

    I was talking about track nuts.

  15. happycheapskate

    happycheapskate Active Member

    Finished making home made spring tensioner

    I rode it 4 miles so far, works great.

    I used the special order screw (have 3 more if you guys want one, PM.) and loctite, and the Tractor Supply Co roller arm. I used a piece of vinyl fuel hose for a bushing, and a small washer, and 2 nuts leftover from the motor kit as jam nuts. The very hard part was bending the spring to fit. I drilled a small hole in the case about 1 cm from the edge for the spring to pin against the case for torsion.

    Perhaps someone can figure a better way to bend and fit the spring or a better spring to use. [​IMG]
    Last edited: Apr 20, 2010
  16. happycheapskate

    happycheapskate Active Member

    quick link/master links can cause binding

    I have a KMC Z chain which is nice. I've always had good luck with these chains on any 1x1. But the small driver cog on the engine side does not like the master link.

    I rode for 40 miles today, and the chain jumped 2 times. One seemed completely due to a huge pothole at 10mph when I accidently goosed the throttle. The other occurred while pulling uphill at low speed. The chain slackens to the degree possible if the torque of the engine vs the speed of the wheel, can overcome the force of the tensioner.

    I moved the wheel back to just under as snug as I would run it with no tensioner. This seemed to do the trick all the 20 miles back home, but I'm still going to put a normal link in place of the master link.

    If you use a spring powered roller on the top run of chain, pull that sucker HARD. All the time you are motoring forward, the chain will be at slightly less tension than that.

    Perhaps a stock type idler wheel and bracket (weld it! ) plus the chain tensioner I made, would be tops.
  17. MotoMagz

    MotoMagz Member

    tsc tensioner with #41 idler

    Happy,This is on that I made out of a tsc tensioner,it mounts on the seat tube.I have brass bushings in two areas so there is no slop the sealed bearing idler is smooth and works good.


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  18. happycheapskate

    happycheapskate Active Member

    Moto Mags. That looks good. Where did you get the brackets that go on the seat tube? Are they drilled out Happy Time mounts? Where did you get the gear wheel? Is that a TSC part for go carts, or did you add it? I like the neoprene roller a lot.

    Does yours spring up on the chain? I think that is the best method, if you have enough force to not derail during pedal starting. If you spring up on the chain, then all the torque the motor can provide will not slacken the chain.
  19. MotoMagz

    MotoMagz Member

    Happycheapskate,the mounts are from and old motorbike 2 stroke but not the happy time type.
    The spring and arm are from the TSC tensioner.I drilled out the post that held the rubber roller. Then added the #41 chain idler wheel.You can get them of Ebay they also work well on the stock tensioner bracket
    Yes it springs upward.

  20. happycheapskate

    happycheapskate Active Member

    Thanks for contributing to the thread. I wonder if the happytime type brackets can work in a similar fashion, since they are for 6mm screws, and I used a 6mm screw with a plastic bushing and it works well.

    The Bikeberry Grubee kit came with an extra block type bracket and an extra couple of thin brackets for various down tubes.

    I've been riding to work again and having a Happy Time again. It is the fun part of my day.