Chain Tensioner Destroyed Rear Rim

slugmustang · May 23, 2010

Hey all. I just put together my first bike this weekend. Its a pretty good looking walmart schwinn beach cruiser (blue and white) with the 7 speed selector. All went smooth with some advice on the motormounts, sticking clutch, and all. I nutted and bolted the whole bike and took it out today on its maiden voyage. I got down the end of my block and let the clutch out....jerk a jerk...it came alive and i cruised down the street....the engine died and I reset the clutch and let out...then BANG!!!! The chain tensioner took a dive into my rear spokes and destroyed the rim. It pulled 4 spokes out and turned my rear wheel into a taco (.01 mile on the bike at this time). Luckily I wasnt going very fast and the bike stayed up when the back end stiff.

I felt like I did everything right, but what the heck happened!?! Has anyone else had this happen to them? Or am I the dummy on this one?

Now my questions are...where do I go to find a cheap rim for a 7 speed carriage and what size do i need for a 26x2.125 tire?, and where do I get a tensioner that wont detonate on its first 30 seconds of operation????

:-||

THANKS,

Justin

5-7HEAVEN · May 24, 2010

I've never run a frame-mounted engine, but here's my take on chain tensioners. No amount of tightening can ensure that this will not happen again with a bolt-on tension with a pivoting bracket.

My solution? Weld on a flat slotted tab of metal .weld

that you will bolt on a skateboard wheel....

orrrr bolt on a flat metal bar, connecting the frame stay to the seat stay. Then bolt a skateboard wheel on, to act as chain tensioner.

Ya might have to fab an aluminum "wedge/shim" to get the skateboard wheel perpendicular to the road.

JMO, nothing short of a framebending accident will send the tensioner into the wheel spokes.

2door · May 24, 2010

You are by no means the first victim of the slipping chain tensioner. In retrospect you could have researched this forum for numerous ideas about how to prevent what happened to you. Its an old story that has been addreesed here time and again. The stock, kit supplied chain tensioner brackets are notorious for loosening and rotating into the rear wheel, which as you now know can and will destroy it. Some will tell you to get rid of the tensioner alltogether and run without it. That's good advice 'IF' you have room in your rear dropouts for adjustments for chain tension and 'IF' you have adequate chain/frame clearance. If you find that a chain tensioner is needed then the tensioner bracket must be secured to the chainstay in such a way as to prevent it from rotating inward. One option, frowned on by some, is to drill a small hole completely through the tensioner bracket and bike frame and install a small diameter screw/bolt that will hold the tensioner in place. Another option, the best actually has already been suggested. That is to weld the bracket or fabricate one and weld it to the chainstay. The kit supplied tensioner wheels in some kits are not the best quality and will fail after a few miles. That has prompted many to replace that plastic wheel with a modified skate board wheel which will contain bearings and be made of a material which will stand up to the rigors of a chain drive system. Many have had good luck with a polyurathane wheel, grooved to fit the width of the chain. I'd post a link for you to read and see what others have done to correct this problem but there are so many that I would suggest you use the search feature and simply type in 'chain tensioner'. There's enough reading there to keep you up all night.
Tom

ThatPerson · May 27, 2010

What you should do is go down to the local hardware store and pick up a piece of flat stock steal and some rubber coated clamps and duplicate what I built for my uncle's bike. I found the design on this site and I can tell you that it works great. If you pull this into the spokes, something went really wrong!

happycheapskate · May 27, 2010

You can obtain another wheel from -- Bicycles, Bike parts, Mountain Bikes, BMX, Road Bikes, Haro Bikes, KHS Bikes, Felt Bikes at Niagara Cycle Works for probably $20-70 depending on how fancy you want. You want a 26"x1 or 1.5 wheel. It is the most common size, and is not the old 26" fractional road tire size from 80's American bicycles.

You can get another tensioner from gasbike.net. Look for the one with double clamps.

What happened to you is a common accident with motor bicycles.

If you must use the idler tensioner, please have it tack-welded to the frame. You can do this by removing your spark plug, mounting the idler and adjusting as necessary, then pushing/pedalling the bike at low speed to test alignment and tension.

Now have a mechanic or welding shop (try ag-class at the local high school, or a college course on welding for lower labor costs and eager workers) take your order.
Tack weld the taller piece to the frame (steel, right?) in the corners where it touches the frame, then remove the bolts and clamp pieces, and continue welding the tall piece where it contacts the frame. Reinstall the clamp and bolts. You should be set, now.

If you cannot get it welded, or its an aluminum frame, you can use a rubber shim, such as a bicycle tube cut to fit, and put loc-tite on the mounting bolts.

The cause of the failure to keep from rotating is caused by an ill fit between the clamps and narrow chain stays of road bicycles or various multi-geared bicycles. I put the idler on my beach bike and I could not rotate it because the shape matched the thick stay on the bike.

slugmustang said:
Hey all. I just put together my first bike this weekend. Its a pretty good looking walmart schwinn beach cruiser (blue and white) with the 7 speed selector. All went smooth with some advice on the motormounts, sticking clutch, and all. I nutted and bolted the whole bike and took it out today on its maiden voyage. I got down the end of my block and let the clutch out....jerk a jerk...it came alive and i cruised down the street....the engine died and I reset the clutch and let out...then BANG!!!! The chain tensioner took a dive into my rear spokes and destroyed the rim. It pulled 4 spokes out and turned my rear wheel into a taco (.01 mile on the bike at this time). Luckily I wasnt going very fast and the bike stayed up when the back end stiff.

I felt like I did everything right, but what the heck happened!?! Has anyone else had this happen to them? Or am I the dummy on this one?

Now my questions are...where do I go to find a cheap rim for a 7 speed carriage and what size do i need for a 26x2.125 tire?, and where do I get a tensioner that wont detonate on its first 30 seconds of operation????

THANKS,

Justin

Alson · Sep 10, 2010

I used a plastic garden hose, cut the size split it in half and put dubble sand paper, well not rrrealy sand paper but dry wall sand paper it like a screen you can see through, but works like sand paper, put a pice in the inside and a pice on the out side, and bought new boults for the bracke, hold very well. The outher ways that were said sounds good, just thought Id tell ya what I did cvlt1

KCvale · Sep 10, 2010

slugmustang said:
Hey all. I just put together my first bike this weekend. Its a pretty good looking walmart schwinn beach cruiser (blue and white) with the 7 speed selector.

Justin...
Your Wally World Schwinn didn't need a drive side tensioner at all, nor did you have to mess with the pedal side with a 7-speed derailer, it has a tensioner.

So you broke some spokes and no doubt bent the rim a bit.
Take the back wheel off and to a local bike store and ask them how much.

If it is over $75 just go buy another Wally bike and use it's wheel.
Chances are you will need other parts from it as well anyway eventually, and please, for heavens sake, buy a chain link breaking tool as well and forget the drive tensioner, you don't need one on that bike.

Just another 2¢ from the 'drive chain tensioner nazi'
At 2¢ a pop I must be like at $2 by now hehehehe ;-}

Really though Justin, don't add parts that can do this kind of thing you don't even need.

rimotorbiker1976 · Sep 10, 2010

oh man good thing you didnt get hurt, take the engine off the bike clean it up real good take the sproket off the wheel put it back on,bring the whole thing down to wallyworld walk up to the return desk and say "look at this, i was riding down my street and hit a bump and this wheel disintegrated on me,i could have been killed")theyll probably give you a new bike.

KCvale · Sep 10, 2010

haha, good idea rimotor.
They might indeed just replace it.

DudeZXT · Sep 10, 2010

This kid posted one time in May and has apparently never returned. I wonder how his motorbicycling experience is going, nowadays...

allen_okc · Sep 10, 2010

i bolted mine to the seat post and the lower part of the fram - i had to make my own bracket, but its worth it to fabricate a bracket that uses two bolts or welded on...

KCvale · Sep 10, 2010

DudeZXT said:
This kid posted one time in May and has apparently never returned. I wonder how his motorbicycling experience is going, nowadays...

Hahaha, just noticed that once you mentioned it.
Not uncommon I suppose.
Still not a bad idea to see if Wally would just replace the bike, they only pay like $50 for them.

slugmustang · Oct 23, 2010

DudeZXT said:
This kid posted one time in May and has apparently never returned. I wonder how his motorbicycling experience is going, nowadays...

As a matter of fact, I stole the rear rim off my dirt bike...which had the right carriage for the schwinn and im back in businitz. however the clutch is now slipping like a mo fo, but im cruizin like none other with the solid chain tensioner that I fabricated (when I can get the motor started after several attempts of poppin the clutch)hehhe. Rock on, thanks for the advice. PS this is my second post, and yes im still around! auflg

allen_okc · Oct 27, 2010

hey kip harley - do you have a photo of the bike so i can see how the frame structure is shaped.

i do know that a clamp style tension pulley is doomed to fail, unless it has been mount top and bottom so it cant spin on the frame...

allen_okc · Oct 27, 2010

i agree with you kip - the tensioner shoud be mounted with the structure of the motor - that dangerous item they give with motor kits is very dangerous, thats why i went with a different set up. i saw the way they wanted us to install the tensioner, i didnt like it all...

happycheapskate · Oct 31, 2010

I installed the stock tensioner on the pedal side, aimed down toward the ground. It works very well on the thick beach bike frame and stays tight. The wheel would contact the rim at worst if it did loosen, not the spokes.

The stock idler can work well on some frames, but seems to be very dangerous on road and mountain bike frames because of the clamp shape.

I recommend welding it to a steel frame, or making the brace type chain tensioner if you don't want to get involved with spring types.

Elixys · Oct 31, 2010

WHOA WHOA WHOA!!! stop for a second. firstly you got the bike at walmart. take the motor, gas tank and any evidence of it being motorized off the bike, load it up in a pickup truck, and take the whole bike back to walmart (with the receipt of course) and claim that the bike was defective. this should get you a new bike to work with rather than trying to peicemeal a new back tire.....

huh....i didnt notice how old this post origionally was......

kipharley · Oct 31, 2010

Wouldn't that be illegal?Kip.
[email protected]

kipharley · Oct 31, 2010

allen_okc said:
hey kip harley - do you have a photo of the bike so i can see how the frame structure is shaped.

i do know that a clamp style tension pulley is doomed to fail, unless it has been mount top and bottom so it cant spin on the frame...

Here's a pic of the bike before I designed and built the motor mounted tensioner. Kip.
[email protected]

allen_okc · Nov 1, 2010

good lookin bike - the simplest thing to do would be to drill a hole into the bracket and into the frame maybe go all the way through and nut and bolt it. that should help hold it in place...

as far as a new rim, a pond shop should be the cheapst way to get bike parts... buy the whole bike for 30 to 50 dollars...

Chain Tensioner Destroyed Rear Rim

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