Idea for chain tensioner fix

[TheNecromancer13]

So I'm installing a motor on my bike this weekend, and I've been reading up on all the problems I might run into. I noticed that the chain tensioner seems to be almost universally hated because it comes loose and falls into the spokes and makes you crash. So I've been trying to think of ways to fix it, and I thought of a few ideas and was wondering if anyone else has done this...

Once I try one, I'll post how it worked.

#1) Take a strip of metal, drill a hole through one end, and install the tensioner like the instructions say, except where the little pulley attaches to the metal arm, take that screw off, and put the metal strip on first, then put the other stuff back on (so that when I install it, the metal strip is on the outside and the pulley is on the inside). Then, when I install the tensioner, I put the metal arm on the horizontal bottom bracket, and then, once I've got the tension right, I attach the metal strip to the diagonal upper bracket, maybe with one of those clamps you use to fix a garden hose and some old inner tube or something (I'll have to see what works when I get the kit). That way, the pressure of the chain can't force the tensioner sideways into your spokes, and it will have to get a lot looser before it fails, and even if it does, the failure won't involve screwing up my spokes.

#2) Extend the metal arm on the stock chain tensioner, and mount it from the diagonal top bracket, so that it goes down past the top chain, and pulls (instead of pushes) the bottom chain up toward the diagonal top bracket. This would make it so that the pulling force of the chain does not exert leverage in a direction that would force the tensioner into the spokes, instead it just pulls it straight out, so again, even if it became loose, it would still function and I would notice it loosening before it got to the point where I crashed. Might have to bend the arm to move the metal out a bit so the top chain doesn't snag on it.

#3) Share your own ideas, if they're better than mine I'll use them.

 

[GoreWound]

Arched chain tensioner
I linked a place to buy them but I am sure you could make one of these yourself.

Also, if your frame has horizontal rear brackets and allows for it you might be able to not use the chain tensioner at all.
seen here, just managing it

 

[Davezilla]

I like that arched tensioner bracket... Use that bracket with a small sprocket on a real bearing, problem solved.

The tensioner wheel that comes in the kit really leaves a lot to be desired and the bearing wears out fast too... A lot of people have switched to a rollerblade wheel that's been shaved down, the plastic is softer so it rides quieter and the bearings are way better too. If I remember right, there is a member who makes these and sells them in the "for sale" section in here... The rollerbladde wheel type pulley will be the quietest running and the sprocket type will help with chain tracking if needed, but both work really well for what they do.

 

[2door]

The concept of spanning the seat and chain stay with a tensioner bracket isn't new. The idea has been around for a while. It is by far the best alternative to mounting the tensioner, if you must use one. Obviously the superior route would be to run without a tensioner but some bike frames don't lend themselves well to that method.

The hazards and short falls of the kit tensioner is well known and it has been discussed here at length. The OP's idea is a good one as long as the bracket is securely mounted. I'm not convinced that his hose clamp idea would be the best method of attaching a bracket that is under a surprisingly amout of stress when the bike is under engine power. Fabricating clamps and bolting the bracket would be a better alternative and of course welding would be the best.

Another idea that doesn't get much attention anymore is drilling a small hole through the tensioner bracket and the chain stay and using a small diameter bolt to secure the bracket from moving. I don't want to open a can or worms here because that method was hashed over time and again and usually ended in heated discussions both pro and con. Lets not get into that one.

One thing that must be addressed with any kit bracket is the need to bend or twist it so the tensioner wheel aligns with the chain path. The bracket, as recieved in the kit and installed without bending will almost without exception cause the wheel to bind against the chain, pull the chain out of alignment with the sprocket and usually end up in the spokes with the expected results. The wheel centerline must be aligned with the chain and that requires the bracket be twisted to take into account the front to rear taper built into most chain stays.

Tom

 

[Davezilla]

Very true... there's no way I'd trust those little hose clamps there... Personally I'd weld it into the frame, but some good billet clamps would be nice.

About the drilling into the frame to steady the stock type tensioner... I wouldn't do it but others have done it successfully. I'm just using the standard 2 bolt tensioner myself and the way to get to not slip is to install it where it needs to go but make sure the bolts won't bottom out or the clamp isn't shut on both sides just running the bolts down by hand. Some prefer that both bolts go down evenly, but I prefer to set the clamp where I want it and tighten the top bolt all the way down and torque it, this alone will steady it, then go and tighten and torque the bottom bolt, there should be a gap down there after torquing, if there's no gap, it bottomed out first and will also be able to slip.

Now look at the roller position with the chain installed and tensioned loosely for now. Is the roller parallel with the chain? if so, good, your done and can set tension. If not, then you'll need to put a twist in the bracket so the wheel will be inline and parallel with the chain. This bracket is pretty tough but it will bend a little without applying heat to it.
I found the best way to bend or twist something like this is with a 12" or larger crescent wrench, set the jaws so they'll fit over the bracket and now ya got enough leverage to do the twist. If you see the frame moving instead of the bracket twisting, stop here, remove the bracket and put it in a vice. You can also heat it up with a propane or map torch if it's still too tough to twist or if you're trying to be really precise with it. the amount of twist needed is trial and error when off the bike so try and get a good idea how far it needs to go before removing, you'll only know if it's right or not by reinstalling so definitely pay attention here when eyeballing it...

Of course, if you can run the chain without a tensioner, this is best, quietest, and the most reliable since there's one less part that can fail, if the tensioner is definitely needed, then there are some good ideas you can use to get yours where ya need it.

 

[Trey]

13- What frame are you building on? As mentioned, some require a tensioner. For others you have the option of using none at all.
I only use them if the owner demands it. I explain the dangers, about how you described them, and do whatever they want. Once, it was a 1/8" thru rod, and that is still in good working order after many miles. I would not drill a hole in my frame, but this guy tows a trailer and loves WOT, and I see no cracks, bending or wear in the hole.
If you choose to do away with the tensioner, pay attention to gear/chain alignment and tension, and you should be able to work it out without too much worry. Both topics are well covered here, just use the search bar at the top.
If you can, post pictures. We love those!

 

[mapbike]

Like 2door said we don't want a huge debate, but I can say that I for one have no issue with a small hole drilled through the indler/tensioner bracket and then on into the frame to secure the bracket, much less chance of the tiny little hole causing an issue than there is if the tensioner rotates into the spokes and destroys the wheel and possibly sends the rider over the bars.

On my Kulana bikes the lower frame tube is oval instead of round and the bracket can't rotate on it at all unless it became so loose in could almost fall off.

As it has been said multiple times, no tensioner at all is best if possible but its best to do whatever is necessary to secure it solid if one is used even if that mean a small hole in the frame and a small sheet metal screw to insure the bracket doesn't move.

 

[woogie_man]

I was able to make a tensioner with a shaft collar, with two nuts welded to it. Then I used a small skate board wheel as the actual tensioner. The layout of the bike allowed me to attach it to the seat post tube. Plenty of adjustability, and it looks good to boot.

 

[maniac57]

The single biggest issue I see from newcomers is the twist that Davezilla mentioned...
Once you get this right, tack welding the bracket is my preferred method.

 

[cannonball2]

I was fortunate enough for the chain line to allow the idler to be mounted under the engine. Look how the stock idler bracket fit the 1" tube, like it was made for it. Look at the size of the chain stay in the pic. There is no way this stock unit would have clamped that properly! If you are going to use the stock bracket, for sure weld it once the chain line is established! http://motorbicycling.com/showpost.php?p=593005&postcount=13

 

[mapbike]

May not be the best place to put this but just in case someone reading this may be interested, I just thought I'd throw this in and hope no one cares.

I make the idler/tensioner wheels from skate board wheels, I use high quality bearings and I use bearing spacer between the bearings which prevent crushing the bearings, I do leave my rollers larger diameter for better contact area, I sell mine for $12.00 shipped anywhere in lower 48 for free with an axle bolt, nuts and washers.

The price I charge, mainly just covers wheel & hardware parts, postage, packaging and about $3 for my labor.

I haven't advertised much on here, but a few members here have got one from me and as far as I know they're still working great just like all of mine are.

The rollers made from the tough urethane wheels are much better than the kit rollers.

Map

 

[2door]

Just a word or caution about 'skateboard wheels'. They are by far the best alternative for a tensioner wheel but you need to watch out for what you plan to use.

Some of the cheaper wheels are two layer, laminated wheels. The outer skin, or layer will come off like a truck tire retread when you try to cut a chain groove in them leaving you with a hard plastic inner core that is no better than the kit tensioner wheel.
If you opt for making your own look for skateboard wheels that are one piece urathane usually molded in a translucient color and not the black ones with a white inner rim.

Just thought I'd toss that out there to keep you from making the same mistake I did a few years ago.
Incidentally there is a very old thread here somewhere about making tensioner wheels from skateboards. If I find it I'll post it here. The advantages are, hardle any wear, less noise and the good ones usually come with bearings as opposed to cheap steel bushings.

Tom

 

[Trey]

Here's the link Tom.
I hope this is the one you mean, you gave a couple good links in this one...

http://motorbicycling.com/showthread.php.?t=39610

Trey

 

[mapbike]

The wheels I use are one piece although I have made some from two color wheels that have been working fine for several years.

The bearings that come with a lot of the wheels aren't that good so I order the bearings separately and they don't normally come with spacers to keep tension off of bearings so I order those separate also because they really need it, all I buy now though is the solid wheels like Tom mentioned, I like them better and the density of the plastic is better, you can tell a difference in how they cut on the lathe when shaving down the sides and cutting the chain groove.

Another thing you have to watch out for when buying skateboard wheel bearings is the one that look good but have plastic inner races and only have a seal on one side, I've ordered bearings and got some of those once.... they're loose and wouldn't last very long.

The right wheel, machined down right for proper alignment and good quality bearings and you can have a very durable idler wheel for the tensioner.

 

[2door]

Thanks Trey. Seems that second link is dead but here's another one > http://www.google.com/cse?cx=partne...#gsc.tab=0&gsc.q=Skateboard wheels&gsc.page=1

Tom

 

[Trey]

That was just a couple of months before I was able to get back online. Missed the whole thing
And thanks for the fix.

Map- People say good things here about your work!

 

[maniac57]

Were you selling the blue grooved roller map? I bought one off ebay some time back and it's still in service on my lawn mower as a belt tensioner! Very nice part for $10...

 

[mapbike]

Were you selling the blue grooved roller map? I bought one off ebay some time back and it's still in service on my lawn mower as a belt tensioner! Very nice part for $10...

No sir, I haven't put any on ebay, I've thought about it but just never done it, if what you got has bearings in it like I use it should be a good one for sure, I also pop the seals off the bearing I use and pack them with good grease since none of them come with hardly any lube in them.

 

[maniac57]

Yeah it has very good bearings. Only issue I ever had was finding a proper preload spacer to prevent the bearings from crushing when you tightened it. Once I got the right part it has been bulletproof. I used it on two or three bikes and aside from the grease, it looks the same as the day I got it.
I live in Memphis and my mower gets used two times a week all summer. You can almost WATCH the grass grow.

 

[TheNecromancer13]

Fixed it! So I came up with a really simple solution: I mounted the chain tensioner like it said to, except I put the chain under the roller instead of over it. Also I took a hammer and slid the teeth of the nail puller on either side of the bar and used that to get some leverage to bend the pulley so that it was aligned with the chain instead of the bar it was attached to. Now it works great, and I don't have to worry about it falling into the spokes if it becomes loose.