Upper chain tensioner

[SpikeFC]

Has anybody ever done this? I've seen only tensioners running on the lower part of the chain like here:

Question is - is it even possible? I might have a problem with a chain that can't clear the seat stays, and I want to avoid cutting the frame.

 

[MattiThundrrr]

Not sure I've ever seen one above the stay, but I found a few ideas. This is a motorized bike, but looks pretty cool

One like this looks like it could be flipped to tension the chain above the stay

Or a ghost ring might work for you, and they mess with people's heads!

 

[Psychographic]

When you pedal a bike all the slack is on the lower part. You pull a chain, not push it.

 

[SpikeFC]

When you pedal a bike all the slack is on the lower part. You pull a chain, not push it.

Yes, but the problem lies somwhere else...

I will make a thread for this baby in the Builds section by the way. Originally I wanted to wait with it for the Build-Off #15, but... I just can't wait, and I probably would not finish it in 4 months time And I'm also so excited about it, that I sometimes can't go to sleep if I don't solve some problem with it.

The problem is right here:

This frame is designed for 10-12 year old's and for super rare 22" wheels. I installed an MTB fork & 26" in front, and a 26" electric wheel in the rear using a subframe. I don't want to modify the existing frame, and if the subframe is straight basically this thing looks like a monster truck, and not like a 1910's racing motorcycle. The problem is in two places:

*below the place where the subframe connects to the dropouts - but there I can use a tensioner.

*above the same place. In a normal bike there should be a sprocket there, but this babe has it's tire there. (marked with red)

My idea was to buy two engine chain tensioners like this:

And run one on the seatstay to tension the upper part of the chain, and one on the chainstay so it would pass the original dropouts. (So the chain would go like the grean lines. I'll be running a 16T on the wheel and 40T on the crankset.)

I know that I'm kind doing this "the hard way" I could just cut the original frame & re weld it to a new shape, but.... no "buts". Just no easy way for me.

 

[Grant]

Not sure I've ever seen one above the stay, but I found a few ideas. This is a motorized bike, but looks pretty cool
View attachment 113455
One like this looks like it could be flipped to tension the chain above the stay
View attachment 113456
Or a ghost ring might work for you, and they mess with people's heads!View attachment 113457

A ghost ring only works with small chainrings like mountain bike ones. Big ghost rings rub against the chainstay.

 

[Grant]

https://ratrodbikes.com/forum/index.php?threads/has-anyone-else-used-a-ghost-ring.108106/

 

[SpikeFC]

In my case the ghost ring would not work. It makes the chain go higher, while I need to make it go lower

I've seen upper chain tensioners, mostly on freeride or BMX bikes, but they are mounted just next to the crankset, and that gives me basically nothing.

Question is - will it affect pedaling if i put an upper tensioner in the middle of the chain? Make it harder, or make loud noises? I know that 90% of the work will be done by the electric motor, but still...

 

[Psychographic]

I don't know if I would trust that nylon wheel. Maybe you could use the bracket and swap the nylon wheel with a jockey wheel that uses a bearing.

https://www.ebay.com/itm/1pc-Bicycl...var=631955719350&_trksid=p2057872.m2749.l2649

 

[pebblewurm]

It looks like what you need is an idler pulley or sprocket, not a chain tensioner. The idler is not spring loaded- it is fixed to hold the chain in place. A sprocket spinning on a bearing held in a fixed location will give you the chainline you need and not too much frictional losses. A quick search turned up the Polish term "
rolka napinacza" for something similar on a belt accessory drive.

 

[SpikeFC]

It looks like what you need is an idler pulley or sprocket, not a chain tensioner. The idler is not spring loaded- it is fixed to hold the chain in place. A sprocket spinning on a bearing held in a fixed location will give you the chainline you need and not too much frictional losses. A quick search turned up the Polish term "
rolka napinacza" for something similar on a belt accessory drive.

Exactly what I was thinking of. This thing is not spring loaded

I don't know if I would trust that nylon wheel. Maybe you could use the bracket and swap the nylon wheel with a jockey wheel that uses a bearing.

https://www.ebay.com/itm/1pc-Bicycle-Rear-Derailleur-Pulley-Jockey-Wheel-Road-Bike-Guide-Roller/362804100310?ssPageName=STRK:MEBIDX:IT&var=631955719350&_trksid=p2057872.m2749.l2649

Well it's made for a bicycle engine, so I think it should withstand use of a normal chain.

 

[Psychographic]

I did the same thing as you are doing. I used a second BB, mounted a trike freewheel adapter with two sprockets on it and two chains. It makes a very clean looking setup.

 

[SpikeFC]

I did the same thing as you are doing. I used a second BB, mounted a trike freewheel adapter with two sprockets on it and two chains. It makes a very clean looking setup.

View attachment 113556

Technically this would be the best option, but I don't have the space to mount that second BB. The only option would be to mount it super low, thus leaving even less clearence than it already has...

 

[Dizzle Problems]

Just throwing it out there, but does the electric set up you’re using have a throttle? Would skipping the chain/pedaling be an option?
Like instead of a crank, use the bb are to mount foot pegs.

 

[SpikeFC]

Just throwing it out there, but does the electric set up you’re using have a throttle? Would skipping the chain/pedaling be an option?
Like instead of a crank, use the bb are to mount foot pegs.

Not an option. It's illegal in PL.

 

[Wildcat]

I agree with the above idea, a fixed guide on top. Solid with no slack. Then a tensioner on the bottom should take up the slack and solve the problem.

I tried a tensioner on the bottom, but with a coaster brake. Failed. There's too much pull on the drive side (or the brake side of a coaster) of the chain for a tensioner to handle. It won't last a day.

I'd like to see what you finished setup looks like.

 

[Grant]

Look at the welded on rear tensioner on this one.

 

[HuffnPuff]

Can you put a rear hub in there and run two cogs on it then run a double chain? Could change the ratio for better gearing by using different sized cogs.

Edit: Scratch hat, I see a tyre in the way.

 

[SpikeFC]

Can you put a rear hub in there and run two cogs on it then run a double chain? Could change the ratio for better gearing by using different sized cogs.

Edit: Scratch hat, I see a tyre in the way.

Eyup, tire is in the wat, that's one, and the second - it will become to complicated. I want it to run, a single speed.

I already managed to put the BB & cranks in place, and figure out the lower tensioning (with a derailleur), and tommorow I will do some work on trying to tension it with an upper tensioner.

 

[SpikeFC]

It works!