Need help with chain tension problem.

Misk

New Member
Jan 14, 2018
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0
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25
Okay, so I'm new to this website, and I was looking for some possible answers to my problem for my recent motorized bike build. I have had this build up and running plenty of times, and everything checks out. No leaks, no broken parts, and it idles fine; however, it cannot go above 20 mph. When I approach 21-22 mph, it forcibly slows down, and this is due to the chain tensioner not moving. This is because in order for me to get it aligned, I had to wedge some metal where the nut goes. Putting this now not-so-relevant information aside, I decided to just go without a chain tensioner, because it has been nothing but trouble. Now I have a new problem, the chain is much too loose, with around 3 inches of slack. Of course, I tried cutting down the chain just one link, and it was suddenly too tight to close, no matter what I tried. The wheel cannot be pushed back, as it is vertically taken out of the bike. If someone could please suggest anything to help, maybe a certain tensioner that doesn't cause a ton of frustration, or a way to get the chain the exact length, I would greatly appreciate it. I am able to send as many pictures as needed.
 

Chaz

Well-Known Member
Jun 3, 2012
1,004
70
48
Vancouver, British Columbia
I'm not sure what you mean about the tensioner moving or not moving. It shouldn't move unless it is a spring type design. You are much better off to get the chain to the right length so you can run without a tensioner at all.

The best tensioner I've ever seen is this "arch type":
http://custommotoredbicycles.com/pa..._chain_tensionerswhite_idler_wheel_415_chains

You can buy these half links to help fit your chain with more precision. https://www.gasbike.net/collections/bicycle-chains-sprockets/products/415-half-link-half-locks

There is some other reason that your bike speed is limited. I don't think it is because of the chain.
And yes, post a photo or two which can helps.
 

Nashville Kat

Well-Known Member
Apr 20, 2009
1,497
48
48
Jacksonville, Florida
https://www.ebay.com/itm/MTB-Bicycle-Bike-Single-Speed-Converter-Chain-Tensioner-Light-Weight-Aluminum/322580535278?_trkparms=aid=555018&algo=PL.SIM&ao=2&asc=49565&meid=1326bf336b7447bb981ce50cf30e5521&pid=100005&rk=2&rkt=6&sd=311984406060&_trksid=p2047675.c100005.m1851

You can also do one of these on the pedal side chain- probably have to get another longer chain for it, too. though. A derailleur on that side does the same thing - tensions the slack on that side- then you can just set the motor chain without matching the chains.

My two builds have never had tensioners- it helps to have smaller sprockets for chain stay clearance- a smaller circle. They are both cruisers too with wide stays.Matching chains can be tricky and the motor chain always stretches more than the pedal chain- so may need re-matching in a year or two. After much experience as a bike mechanic, cutting and setting the heavy motor chain is still the hardest aspect of motor bicycling. I always use a 415 industrial trike chain which as smaller plates and that makes it a little easier- much lighter and better rolling too.

If your drop outs are vertical that may be even more tricky- I'd look into a spring loaded chain tensioner that mounts to the motor- I think there are listings on ebay. That may be the cheapest and easiest solution though I've never used one, I hear they're good

https://www.ebay.com/sch/i.html?_fr...&_nkw=motorized+bike+chain+tensioner&_sacat=0
 
Last edited:

jolfstn

Member
Oct 30, 2011
112
1
18
Seattle, WA
I've come across this issue, I omit the chain tensioner on my builds, and adjust tension via the back motor mount shimmed on the seat post, using multiple washers on the mount bolts. I've had good luck with this and have not needed a chain tensioner. Also: A very tight chain will loosen during the break in to ideal tension.
 

Nashville Kat

Well-Known Member
Apr 20, 2009
1,497
48
48
Jacksonville, Florida
No problems with the motor shifting to the side then jolfstn? I've had that happen before with stock mounts- usually pulling it back toward the motor sprocket side.are you running anything special on the front mount?
I can't imagine you'd get more than a 16th of an inch with a shim or 1/8 tops.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
156
63
USA
before motor mounts were understood well, some folks used to fasten on a 'torque stop' to keep motor from rolling down to the left - haven't seen anyone mount one for many years now, but they work well

should be threads on the board somewhere