Chain Tensioner has 66cc chain tensioner evolved yet; suggestions?

Discussion in 'Transmission / Drivetrain' started by windbreaker, May 17, 2012.

  1. windbreaker

    windbreaker New Member

    the kit-supplied white plastic idler wheel is junk; what is considered to be the best, easily fabricated system (without welding), you folks are using to reliably tension your chains for more than 5 minutes?

    I ride a 20 mile round trip and am sick of repositioning the idler every day. The final straw was when the plastic popped off, the chain jumped off & jammed against the drive sprocket likely bending/cracking the aluminum case. I'm thinking of trying a sprung derailleur as I've seen posted somewhere but have doubts as to how long the plastic cogs will last. there has 2b a better way?


  2. The_Guy

    The_Guy New Member

    Forgive me if I'm wrong, but could you not take the plastic cogs off the derailleur and replace them with metal cogs of the same size?
  3. JunkyardDog

    JunkyardDog Active Member

    I have found what I believe to be the answer, though it will likely require welding. I have not done it yet, but don't see how it can go wrong. Years ago, I had an old dirt bike, a Yamaha MX175. It had this really cool chain tensioner on it. Todays dirt bikes do not have them, and I've often wondered why, since it worked so well. Basically, it had a bracket welded to the swing arm, and a spring loaded arm bolted to it, much like a spring loaded derailleur. But the neat part of it was that it didn't have any wheels or cogs. Instead it had a thick white nylon rubbing block that pushed against the chain. The chain would cut grooves in it, but only so far. It was the chains side plates that made the grooves. when it wore down to where the chain rollers were rubbing on the nylon, the wear stopped. If you look at most dirt bikes and dual sport bikes today, while they don't have the spring loaded tensioners, they do have rubbing blocks on top of the swing arm, that the chain rubs against. Harley Sportsters have these as well, because the top run of the chain runs right on the top of the swing arm front pivot.

    I plan to weld a bracket to the frame (clamping it might also be an option, but it would need to be a much heavier clamp than what the stock tensioner uses) and fabricate a spring loaded tensioner that will press on the bottom of the chain, taking up all the slack in it, like the stock tensioner is supposed to do, but doesn't. The main differences will be that it will be a lot more substantial, it will be spring loaded to keep constant tension on a chain with tight and loose spots, and it will have a nylon ribbing block, at least 2" wide, that will press against the chain, rather than a roller. I can't see any reason why it won't work, the exact same thing worked well on a motorcycle.
  4. Cavi Mike

    Cavi Mike Member

    Those nylon guides exist for a couple reasons, the main one being that it's impossible to keep a dirt-bike chain properly tensioned when the swing arm is all the way up or down, it would bind when the swing arm was at its mid-point. 2nd, to keep it from destroying the swing-arm.

    It's come to my attention that people don't know the rear sprocket needs to be concentric with the hub. Until people realize this, the only tensioner that will work is an actual tensioner - that is - a spring-loaded one. Technically what comes with our kits isn't a tensioner, it's an idler pulley. A tensioner always keeps the chain taught even as the chain wears or if the sprockets aren't concentric.
  5. JunkyardDog

    JunkyardDog Active Member

    I realize the rear sprocket should be concentric with the hub, but even then, a beefy spring loaded tensioner would do the job of the idler, without breaking. There are several problems with the stock "idler" one it it's flimsiness. The bracket bends very easily, and the plastic wheel is prone to breaking. Another is the method used for holding the bracket in place. simply clamping it around the chain stay will allow it to rotate on the frame. Yet another problem is the narrowness of the wheel itself. It requires almost perfect alignment with the chain. If it is even slightly off, the chain will either break the wheel, or come off of it. Plus the idler is mounted at an angle to begin with, as the chain stay is not straight from the bottom bracket to the rear drop out.

    There is another thread on here several pages long, about using a spring loaded tensioner from Tractor Supply mounted to the seat post. To me that seems to be a major improvement over the stock oem tensioner, but the parts don't seem to be available anymore. It used a much wider heavy rubber wheel with ball bearings. A zillion times better than stock, but I still prefer the rubbing block idea over the roller. With no moving parts other than the pivot, it should be bulletproof. And if it were made wide enough, there would be no danger of the chain slipping off of it from normal side to side chain slap. I have also considered using such a device without the spring. Then it would serve the same purpose of the factory part, as an idler, without being a tensioner. It would be much easier to build and install, and the rubbing block would last forever.

    The first time I installed one of these kits, the tensioner failed twice, the first time the cheap plastic wheel broke, and I was ablle to stop in time to save it. The second time the bracket bent into the wheel spokes, destroying the wheel. At that point I abandoned it and went to friction drive, which has worked beautifully here in southern AZ, where it never rains. But I now find myself wanting to go with a frame mount engine again, maybe 2 stroke, but I am seriously attracted to the $G 4 stroke setups. But both require the same tensioner, unless you can get the chain at just the right tension without it. That is almost impossible to do, because of the pedal chain. You can't get them both properly tensioned at the same time. Another idea I had would be to install the motor chain at the proper tension, then use a spring loaded tensioner (probably a derailleur) to tension the pedal chain. But this would only work on a bike with adjustable drop outs, which many multi speed bikes don't have. The bike I plan to use is a former multi speed, converted to a single speed, and has vertical dropouts.

    My main reason for wanting to go with a frame mounted engine is looks, as the friction drive works fine. Yes, I admit it, I want to build something that looks like a motorcycle, specifically an antique motorcycle. But it has to be reliable. I also want it to have clean details, which means no threaded rod heated and bent and turned into a clamp. Functional yes, but not pretty.

    Anyway I am still working on some ideas, and have access to both a welder and CAD software. I am determined to come up with something that will work well and look good at the same time. I have come up with several designs that will work, my problem is how to build them. Sure would be nice to have a CNC mill or a laser cutter.
  6. fx-2

    fx-2 New Member

    Chain set up

    Why would you use a tensioner or guide . With master links and half links you can get the drive chain adjusted right . On the peddle chain use the same procedure if it need more adjustment you can change the rear cog . I use this on my bike an there have not had any trouble , works great . The tab off chain stay is for the coaster brake . Dan

    Attached Files:

  7. Fabian

    Fabian Well-Known Member

    Considering the single speed system has so many limitations - chain tension problems just being one of them, wouldn't it be a good idea to junk the single speed and move to a more useful multi-gear system.

    I made the change within 3 minutes of riding my bike as a single speed. It became immediately obvious that climbing a 22% grade was going to be a fanciful idea, unless i was prepared to ride at 3 miles an hour on a level road.
    Having made the change to a multi-geared system, i haven't looked back...

    I still don't understand why people waste their time with the standard single speed kit - It's a bit like driving a car with three wheels
  8. fx-2

    fx-2 New Member

    The reason most use single speed drive is the cost , the kits come with them . When set up right they work well . Most motorized bicycle are ridden on the street , at least here where I'm at . A single speed works fine . Another reason is a lot are built on beach cruiser frames with coaster brakes . A shifter kit an brakes cost much more than the motor kits . Dan
  9. Fabian

    Fabian Well-Known Member

    That's a bit like saying a Ford Explorer comes with tyres. We all know that the first thing you do before driving the car, is replace the tyres with a set that won't explode and roll the vehicle and potentially incinerate the occupants.

    Same thing goes for the standard Chinese bicycle kit:

    1) Replace the CDI witha Jaguar CDI
    2) Replace the standard single speed with a multi-gear system.
    3) Replace the intake with a Rock Solid Engines reed valve intake.
    4) Install a cylinder head temperature gauge and an exhaust gas temperature gauge.
    5) Replace the standard carburettor with a Walbro carburettor.

    Now we have the makings of a reliable motorized bicycle - nothing flash; nothing fancy, just the bare essentials for reasonable reliability.
  10. fx-2

    fx-2 New Member

    Well it not a ford , by way my ford tires oem ran 45k and never went flat or had a blow out . The changes you want to make push the cost up where most would not build a bike . Most builder have trouble getting the kit assembled and the motor properly tuned . The thing is these are a poor choice for transportation , nice to ride on Sunday but not to work unless you want to peddle a lot . The changes I suggested are cheep and well make for a reliable chain drive . Dan
    Last edited: Jul 22, 2012
  11. JunkyardDog

    JunkyardDog Active Member

    I have a single speed I want to use for my next build. But it was not also a single speed. It is an '80s or '90s model Trek Antelope 800, with a very high quality steel frame and Araya aluminum rims with large flanged hubs, stainless steel spokes, etc. I removed both derailleurs, and the larger front chainring. I have the chain on the smaller front chainring,, and on the middle rear sprocket. I got lucky, and got the chain adjusted right in that position by removing links. It doesn't always work that way. The chain will be way to tight or way to loose. This is a very low geared bike, capable of climbing hills, and cruising on level roads, though at very low speeds unless you can really spin it. I put a much more comfortable seat and upright handlebars on it. My original intention was to use this bike as a "canal bank cruiser" We have a canal nearby, over 20 miles long, with a dirt road on both sides, where motor vehicles are prohibited. So it makes a nice place to ride a bike. Unfortunately my knees are slowly getting worse, so I built a Huffy Cranbrook with a Staton friction drive and RS engine. It still works fine, but I now want to build a MB out of my Trek, with either a Chinese engine kit, or a 4 stroke engine kit The main issue with these kits is the chain tensioner/idler. I know that from experience, having destroyed a rear wheel and almost crashed.

    I also came up with the idea of welding a piece of flat steel stock from the seat stay to the chain stay, and putting some kind of super heavy duty roller or rubbing block on it. I believe I've already seen something like that on this forum. It would have to be strong enough to hold the chain in place no matter what.
  12. fx-2

    fx-2 New Member

  13. V 35

    V 35 Member

    Please consider the following points ; Rear wheelstays do not run
    parallel to chain path [ which is straight ] but taper toward wheel.
    This adds to the problem. I wound up cutting the tensioner bracket
    and welding it to the chainstay. I tacked a single corner, tapped the
    bracket to run parallel to chain [ offset on stay ] and welded it solid

    Check out a Sportsman Flyer, they got it right ! Many spring loaded tensioners are coming out. If your running a coaster brake,
    forget having a pedal side tensioner / modded deraileur. I will work
    well on a freewheel hub, but will backlash [ and break ] when coaster
    brake is applied. I learned the hard way.
  14. Hamguy

    Hamguy New Member

    Spring loaded chain tesioner

    Chain tensioner 2.jpg Hi guys! After worrying about chain adjustment on motorcycles I have owned and now with these little bundles of JOY, I decided to fabricate my own version of a chain tensioner. It turned out so well I made a few more and put them on eBAY - Sold 4 the 1st week! First I tried to make one with the pivot point inline with the wheel and found my chain would rub on the pivot bolt. After some head scratching I came up with the idea of moving the pivot LOWER. BINGO! Next was where to anchor the spring to the bike. Drilling a 1/8" hole in my kickstand bracket provided the perfect spring tension with the springs I had bought. The photo shows my tensioner prototype with the 1st pivot hole in it with the new LOWER pivot point welded on. Feel free to copy mine or, take a look on eBay to see a variety of different ideas. Ride SAFE and have FUN!
    Purple Haze likes this.
  15. Purple Haze

    Purple Haze Active Member

    Cavi Mike is right, if the sprocket is aligned perfectly, there will be few if any problems. Most idler pulley problems are caused by the chain being misaligned and pulling to the inside. Also, the idler bracket needs to be bent to align the chain. If all this is done correctly, there should be very little wear on the roller. The new rollers come with bearings, but if you don't care for the plastic construction, a simple fix is to take a skateboard wheel, put it in a lathe, and cut a channel in it. This has been done many times, with great longevity. The best fix, though, is the spring-loaded tensioner. Those quality:jester: gears have a lot of runout in them.
  16. MusiCALpuLLtoy

    MusiCALpuLLtoy New Member


    i attached a moped motor to the back of a 10 speed bike. for a tensioner i used a rear derailer. it works great .
  17. V 35

    V 35 Member

    Could FX re-shoot the tensioner photo ? Black doesn't photo well, and the details are obscured. The bike looks great, love those chain adjusters. Us ' independents ' seem more bent on safe tensioners than the manufacturer does. that's sad.