Chain tensioners

Bikeman08

New Member
Jun 19, 2008
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Hello world, I really flustered, i need another design for the chain tensioner that one that came with the kit really sucks, get to close to the sprokets gets kinda scary. any ideas. I looked on the site and saw some mods, but i dont know where to get the stuff. :rolleyes:
 

mralaska

New Member
Aug 16, 2008
42
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Deerfield, NH
The best thing I have done on my bike so far is remove the chain tensioner. One link is about 1 inch so you only need a half inch of engine movement to fully adjust the chain. I made three shims out of 1/8 in flat aluminum stock which gives me all the adjustment I will ever need. I cannot remember who I got the idea from, but he called the inserts 'T Shirts' because of their resemblance. Just loosen up the engine and drop them in place. If the chain gets too long just remove a link and start over again. The chain runs much smoother now and no more messing with the tensioner or worrying about it rolling into the spokes again.

Edit: I forgot to mention that you may need to lengthen your rear engine mount studs. I made mine longer when I replaced all the studs but I do not remember how much longer I went. I made the longer studs out of m6x1 8.8 threaded rod from mcmaster.com. The shim stock I got from the bin in a hardware store. I think it was an Ace but most hardware stores have it. With a sharp hacksaw blade and a vice to hold it in place you can whip them out in less than a minute each.
 

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Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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up north now
Here's a tip I discovered....put the tensioner wheel on facing outward, that way if the 'chain pulls the tensioner" it pulls it AWAY from the wheel.

That's usually caused by the chain being too tight.
 

Saddletramp1200

Custom MB Buiilder
May 7, 2008
1,445
51
48
Houston, Texas
I mounted my stock tensioner on the bathroom wall, adds that "homey" touch! My Huffy don't need one, and chains are plentyfull and the chain DAX supplies is a better chain anyway. My frame rails are tiny so it won't hold any how without some welding. It has not streched enough to worry about. (C)
 

Jimigunne

New Member
Mar 27, 2009
16
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Corpus Christi, Tx
I have have a cruisier with the 80cc 2-stroke gas engine mod. (the kit that is sold by many dealers on ebay). Am struggling trying to find a workable chain tensioner. Gave up on that stupid nylon roller. I like Saddletramps' idea of just dispensing with the tensioner altogether! But if the cheap Chinese chain is going to be stretching a lot, then one would have to constantly put in thicker shims.
Question is, how much slack do you want on the chain, when pushed in the middle of the longest span, for best performance? 1/2 inch? I am real paranoid about the chain coming up/off from the engine sprocket.... there is no clearance, and I have heard of this breaking the engine shaft keyway. With the stock unworkable nylon roller, and with it set for quite a lot of tension, this was happening. I was only rolling the bike forward with sparkplug removed, clutch pinned disengaged, so it didn't do any damage..... but after moving the bike forward a few feet, the chain started to come off engine sprocket a little bit. It sure jams it up totally! I don't really know why a high amount of tension was causing the chain to start coming off the engine sprocket...but it was. So it seems you can have too much tension, or too little.
 

2door

Moderator
Staff member
Sep 15, 2008
16,335
141
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Littleton, Colorado
Jimigunn,
You are correct. The chain can be too tight or too loose. You want to shoot for 1/2" to 3/4" slack measured at the center of the chain span. As for your tensioner problems do a little research here and you'll find plenty of discussion regarding tensioners. I happen to be a firm believer in them even when using upgraded chain such as #41 industrial chain. Two things you need to watch is proper alignment of the tensioner to the rear sprocket and rear sprocket to engine drive sprocket. I don't like to see much more than 1/4" out of alignment between the engine and rear sprocket but in a pinch 3/8" will work. Most of the clamp-on tensioner brackets will need a slight twist put in them to give you good alignment to the rear sprocket. They are typically straight and the chainstays will have a slight taper so if the tensioner is not aligned you will be guiding the chain off to one side or the other. Many of us have also secured that ugly tensioner bracket to the bike frame with a self tapping screw or a small bolt and nut through a hole drilled completely through the bracket and chain stay. You only need for that bracket to come loose once to appreciate the amount of damage it can do to your rear wheel and spokes. Another good suggestion is to replace the plastic pully with a skate board wheel. You'll need to find a method to cut a groove in the wheel wide and deep enough to allow the chain to pass around it smoothly. Most of the skateboard wheels have bearings instead of those cheezy bushings, they're made of polyurathane instead of plastic and run much quieter. One other thought about your chain coming off; Are you sure your rear sprocket is running true to the rear wheel hub. Lift the bike, clutch disengaged and spin the rear wheel. Watch for wobbles either side to side or vertically and correct any problems there. The sprocket must run concentric to the hub or it can cause the chain to wrap and that can cause all kinds of problems. Get back to us if none of this has cured your ills.
Tom
 
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abikerider

New Member
Jul 7, 2008
219
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Sacramento, CA
Here's the tensioner I just made. Very simple and guaranteed not to twist into the spokes.


Also, it's lighter than the stock chain tensioner!
 
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Mojo

New Member
Dec 26, 2011
60
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33755 Clearwater Florida
hello 2door, i am new here, i am having some issues with my front motor mount not fitting and my Chain tensioner, i also have the schwinn Clairmont, with a RAW brand 80/66cc 2 Stroke engine mounted to it, currently i am using the stock chain tensioner and the issue i am having is that when i start it and ride, or i hold in the clutch and push or ride the bike the tensioner moves toward the inside of the spokes, i have tried using some rubber grip lining the frame of the bike where you mount a stock chain tensioner and it had a slight effect but yet it still went toward the spoke at about 6MPH, the front motor mount is the stock one made for V style frames like any normal mtn bike and the front of the motor sits about an inch from the down tube where it needs to be mounted so i am in need of advise on how to mount it, we have the same frame so i assume you can help, also i would like to get links to where i can buy the items required to craft the chain tensioner you have made, it is well made btw Cuddos !
 
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abikerider

New Member
Jul 7, 2008
219
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Sacramento, CA
Love that design! That's the one I'm currently thinking of making, simple and effective.
How thick is the metal you used? It's steel, correct?
It's made out of 3/16" thick by 1-1/2" aluminum which is strong enough for the application. Also I don't have to worry about rust,it's nice and shiny and it's easy to cut and drill. It's attached to the frame with vinyl coated straps from the local hardware store and 1/4" bolts. I made the slot by drilling a hole at each end and then using a sabre saw to cut the slot between the two holes. The lower end is cut at a 45 degree angle and the upper end is cut to match the contour of the seatstay. The next time I make one it will be a little longer so that the idler wheel rolls on the chain closer to the middle of its length.
Depending on the frame, you will probably need to mount the end straps facing opposite directions like mine so that the idler is in line with the chain. You may also have to twist the tensioner with pliers slightly to get the chain alignment perfect. 2door is right, the alignment between the front sprocket, rear sprocket and chain tensioner is very important and so is getting all the wobble out of the rear sprocket. Good luck.
 

culvercityclassic

Well-Known Member
Sep 27, 2009
3,115
152
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Culver City, Ca
You guys ever think of running no tensioner on the drive side and add one to the pedal side...that’s what I have done to my china doll bikes...works like a charm...learned it from Venice Motor Bikes...

Check out some of my local riders bikes...
 
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Saddletramp1200

Custom MB Buiilder
May 7, 2008
1,445
51
48
Houston, Texas
There is the Your going to work method. You need a vice, and a medium hammer :) Gently flatten the curve in the steel to allow a very tight fit to your frame. Both sides if needed. It's going to be out of alignment. Put the roller pully on it and fit the chain. LOOK at it. It needs to be tweeked. Put it in the vice and use a large cresent wrench to make the angle of the wheel line up with the chain. It must be straight. Sit on the ground and look at it. Works everytime. (c)
 

2door

Moderator
Staff member
Sep 15, 2008
16,335
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Littleton, Colorado
You guys ever think of running no tensioner on the drive side and add one to the pedal side...that’s what I have done to my china doll bikes...works like a charm...learned it from Venice Motor Bikes...

Check out some of my local riders bikes...
Not every bike frame will allow not using a tensioner or some means of guiding the chain onto the rear sprocket without interference with the frame. Also if the bike doesn't have horizontal drop-outs maintaining chain tension can be a problem. Shimming the engine is not a good idea and shortening the chain doesn't always work. A tensioner will make keeping the chain tight much easier than most methods.

As been posted here countless times; IF you can run without a tensioner, good for you, but, if you need one, and some folks do, then it has to be installed in such a way as to keep it from moving and the wheel/pully/sprocket must be properly aligned with the chain path.


Tom


Edit: What we have to keep in mind here is that the majority of builders do not have access to a machine/welding shop or have the mechanical skills to fabricate custom parts such as tensioner brackets. The kit supplied bracket leaves a little to be desired but can be made to work with only a little common sense. Custom brackets are better but not always within the reach of everyone who attempts to motorize a bicycle. This is why I advocate to the newbie ways of making what came with his kit work and not expect him to run out to his garage and build something that he doesn't have the tools or skills to do.
 
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Mike B

New Member
Mar 23, 2011
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Central CA
Yup.

I tried to do without it and it just didn't work.

Bicycles are not designed with the idea of accomidating aftermarket motor kits.
 

abikerider

New Member
Jul 7, 2008
219
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Sacramento, CA
Edit: What we have to keep in mind here is that the majority of builders do not have access to a machine/welding shop or have the mechanical skills to fabricate custom parts such as tensioner brackets. The kit supplied bracket leaves a little to be desired but can be made to work with only a little common sense. Custom brackets are better but not always within the reach of everyone who attempts to motorize a bicycle. This is why I advocate to the newbie ways of making what came with his kit work and not expect him to run out to his garage and build something that he doesn't have the tools or skills to do.
I don't have a machine shop but I do have some tools. All that is required for the tensioner I made is a drill and some bits, a sabre saw, workbench, c-clamp and a file, not much really. The ability to measure and use these tools is needed of course. I would hope most people attempting to make an MB would have some ability to make things, maybe I'm wrong. I think it's well worth the effort to avoid using that tensioner that comes with the kits.