Simple Chain Tensioner Replacement

Discussion in 'Transmission / Drivetrain' started by Timbone, Aug 11, 2014.

  1. Timbone

    Timbone Active Member

    I have put several hundred miles on my bike and I have been obsessing with a simple and cheap replacement for the stock tensioner. I am getting close.

    After several failed attempts with springs, I gave up on them altogether. I just observed the tensioner to see what works best and what doesn't work. You don't need a spring!

    The chain just wants to roll smoothly onto the rear sprocket. That's want it wants to do - so let it! You don't need a little cog. Almost anything will do. The stock tensioner is made of hard plastic for a reason.

    The stock metal piece that holds the roller is plenty strong. Here is what I did to replace the roller:

    For the axle, I chose a 5/16 clevis pin, 2" long.

    Drop a 1" washer (5/16" hole or close) over the clevis pin. Then drop a 2" fender (5/16" hole or close) washer onto the clevis. This is the inside chain guide.

    I made a roller surface out of nylon washers. Couldn't find the perfect size, so I took a 1" washer (3/8" hole and 3/8"deep)and added 3 slim washers (2 on one side, one on another) and superglued then together. This is roughly the same size as the stock tensioner.

    Add another 2" fender washer to serve as the outside guide. That's all the roller is!

    Run it through the metal holder, add a washer or washers for a snug fit and secure with a cotter pin.

    There should be just a touch of play. I am getting good tension with little resistance. The chain is just clipping right over the hard nylon washers.

    Take the time to work seriously on chain alignment. Let the chain run over the middle of the roller surface. The chain will contact the metal roller glides (2" fender washers) but that will not affect a good 415 chain.

    My first tests were great success! Several miles with a 30 mph run! Pulling the clutch and killing the engine allows a super smooth coast!

    Tomorrow, we test with a 12 mile commute to work. Then back! tension.jpg


  2. HeadSmess

    HeadSmess Well-Known Member

    in dont even need a wheel at all...

    roller chain has its own rollers! just a strip of steel as wide as the rollers, pivoted at one end, locked at the other, and a nice chamfer/ramp on the end... havent actually tried it on a pushy yet, but used to work fine on the old gokarts...and made oiling REALLY easy ;) laziness again...

    youre on the right path... SPRINGS ARE EVIL! as tensioners, anyway.
  3. butre

    butre Well-Known Member

    I've got the same setup HeadSmess is describing on my racing mower, and it's survived off roading with a 20+ horse motor and crazy short crawler gears. If it survives that I think it'll survive a 2 hp motorized bike just fine.

    spring tensioners are only particularly useful if you have suspension travel messing with the chain tension
  4. Timbone

    Timbone Active Member

    I thought about making an all metal chain tensioner, but I thought it would produce quite a bit of clatter.My idea was a bolt or a clevis as the axle, and the actual roller would be a metal spacer of appropriate size.

    Don't need to do that, though, as my chain tensioner is a complete success! It is super smooth with little resistance. All the pieces have just a touch of give so the outer guides turn along with the plastic rollers (washers). And with a cotter pin secure the entire works, that's one less screw nut that I have to worry about loosening up.

    My new frame is due tomorrow so when I get all the parts for the new build, I'll take some detailed pics of my chain tensioner.

    This evening I took a little spin around, just because the weather was so nice and I had already ridden enough miles on my real bicycle. I stopped at a stop sign and my clutch failed, killing the motor. I thought at first that maybe the nut on the clutch cable had slipped, but I quickly discerned that a key screw had vanished. It was one of the short screws on the drive sprocket cover, so there wasn't enough pressure to engage the bucking bar. So....I started a long march home. One mile and a half and the rear wheel would not turn.

    Very soon,a guy asked me if I needed help. I told him that all I needed was a 6mm screw. He told me he had tons of screws and ran in to get them. Oh, I neglected to say that, this one time, I didn't bring a single tool. Not even a screwdriver. So,the man quickly returns with a decent display of machine screws but not a single one would fit. He has a Jeep and offered to ride me home, but I told him that I had a full fuel tank and I wouldn't want the gas to leak down on the top of his vehicle. I thanked this very nice guy and resumed the long walk home.

    About a quarter of a mile later, it dawned on me: you idiot! There are other screws on this motorbike. Just find a non-critical one and place it in the sprocket cover. All I needed was a screwdriver!

    I saw a man ahead and he waved at me, then went back into his house. I was debating if I would knock on his door and request a screwdriver when a nice young lady asked me what my problem was. "You have a flat?" she asked. Quickly, I spoke out "I need a screwdriver! My clutch is out. All I need is a screwdriver to fix it". I think it then dawned on her that I had a very unusual bike and she looked very confused. She told me to walk it down a few hundred yards to her house and she would get me a screwdriver.

    We chatted a bit about cycling as I removed a screw from the clutch plate side and placed it in the missing hole on the sprocket side. Success! I thanked the very nice lady and zipped home in just a few minutes. There are still good people in this world.

  5. HeadSmess

    HeadSmess Well-Known Member

    so, did you get her number? :wacko:

    try living in the middle of nowhere where the only thing you hear from anyone when broken down, if anything at all, is abuse hurled from the window of a fast moving car...

    ".......king fa...." is all i made out ?

    of course, a week later when i saw the same, newly licensed, pimply teen at the local shops, he was all impressed with the (no longer broken) bike until i asked if it had been him that went flying past that night, and if he could repeat what it was he had yelled out now we were face to face and he didnt have his buddies with him to act tough in front of...
  6. Timbone

    Timbone Active Member

    That nice woman was married! She just had that married vibe!

    As a road cyclist, I see lots of mopeds out on country roads and they seem so out of place. As for my motorbike, this seems to be a purely urban vehicle. My commute of 12 miles (one way) is really about as far as one might go.

    I've gotten lots of harassment from auto drivers over the years and I am confrontational. I let them know I am not playing around I take my space as best I can. More than a few times I have chased harassing motorists down and they have FREAKED when I suddenly appeared at their door asking them what the hell their problem is. Most of these ppl are cowards and only get aggressive because they think they can get away with it.

    Your guy is a case in point.