3-speed Jackshaft Build Chain Tensioner

I set out to build my first SickBikeParts Jackshaft shifter kit bike on a nice new Giant Suede 3-speed coaster.

It is a heavy duty beach cruiser with front and seat shocks, but a low top bar clearance to bar and the pedal crank is forward of the seat post.

I ordered the 2010 model in the top pic but the only thing they had that was black was the 2009 in the lower pic.

I love the bike and it looked like everything would fit.

I got the JackShaft kit assembled fine too.

Yes, I painted the mounts to match the shiny new Grubee black 66cc GT5 motor with 11 coats of engine paint ;-}

But when I went to install it with the crank so far forward and as low as I have to mount the motor the chain hits the motor!

As mentioned I can't go up, there is no room.

I love the motor where it is, and though I could move it up if I mounted the carb off to the side, that just didn't make any sense to me.

Now I hate putting any tensioner/idler pulley on a main chain drive, but I don't have a choice here so I looked at my options.

I figured I would just see if I could use the otherwise stock kit tensioner pully and I can, but there is a small window I can place it in so it doesn't hit the motor or the now to be main drive pedal chain!

I pondered this problem for two days thinking of how I could add something to the motor to support a pulley and all looked bad until it dawned on me

All I need is a modified right side JackShaft mounting plate like this.

It would look like this from the left where it mounts to the back of the clutch housing.

And from the right side it looks normal and the pulley can move the length of of the bottom of the motor without touching it.

I think with this setup you could even use a crank mounted forward AND above of the final JackShaft motor drive sprocket.

I e-mailed Jim at SickBikes this morning to see if they could offer this plate design as an option with their kits.

What the heck right?
It is just a couple more cuts on a little bigger piece of steel, you can use the otherwise unused kit tensioner pulley, and with the 3 point mount to the motor it sure as heck won't flop around like the stock mount can on a chain rail.

What do you think?

KC's Kruisers.

 

[Fabian]

My solution; you may be able to adapt the idea or just create a new concept that might be useful for everyone else.

http://www.motoredbikes.com/showthread.php?t=23130&highlight=sickbikeparts+chain+tensioner

Fabian

 

[Fabian]

Just thought of another concept.
You could drill into the end of the jackshaft and insert a roller bearing, then place a pin inside the I.D. of the roller bearing and use the pin to hang a dual (spring loaded) idler roller system.
This would have the advantage of being self aligning and not needing to modify the jackshaft plates.

I'll try and draw up an image of the concept.


Fabian

 

[professor]

I think you did real good Kc!
I love seeing the creative side come out in solving these problems.

 

[KCvale]

Thanks ;-}

I heard back from Jim at Sick Bikes, he suggested this:

"In theory I could make you one but to be honest I just don't have time. All you wonderful customers are keeping me and my partner all asses and elbows.

I think you can get away maybe just moving the sprocket to the right. I run mine outside of true alignment anyway to increase the clearance between the two chains. Give it a try."

So I gave it a try.

There is enough room on the shaft no problem and it just clears the clutch plate, but it looks like it will rub on the clear plastic chainring cover.

If so I imagine just a washer or two between the chain guard and sprocket will solve that.
The trick will be to see if the chain wants to jump or wear the sprocket too much.

Only one way to find out, finish building it and try it out.
I sure hope it works, it's killing me bringing it this close and not finishing ;-}

About the link bike with tensioner
I don't see any reason a right mount for that dual sprocket like a derailer coult not be made as well.

Certainly a lot less parts and work.
Cheap too if you have a standard derailer shifter laying around too.

If I had a metal shop I would have made my design, still might, it will sure be easier to adjust the chain tension without having to move the motor up.

Actually, if the plate went down on the topic link page you could use the stock pulley and tighten a straight down chain in a jiffy too.

If I had a bike like that, I could whip up a poster board model for that in no time.
A single flat piece of metal is pretty cheap to make, and you get the tensioner in the bike kit.

KC's Kruisers Glendale Arizona, USA

 

[gasbikeproject]

Shiftkit tensioner

this is what I came up with. Fits on bottom u-bolt of shift kit

 

[Fabian]

Hi gasbikeproject

I like your variation on the theme of using the U-bolt as a pickup point for the chain tensioner. In my opinion it's the only practical method that doesn't involve modifying the shift kit plates.

There seems to be a need for a decent chain tensioner for the SickBikeParts shift kit.
We should start a sticky thread for the things, to get everyone's solution in the same place on the site.

Fabian

 

[Ghost0]

Well in my opinion, and I think I deserve to have one since I designed the thing, if you need a tensioner then you are masking a problem that you shouldn't have. I have never needed one and most other customers have not needed one either. I will admit it is a bit of a balancing act getting the engine at the correct height and the chain length correct. Every bike will have a sweet spot where the engine just likes to sit and if you can achieve the correct chain length in that position you should not need a tensioner. KC's issue is a bit different as he is using a bike that is a bit different with his bottom bracket far in front of the seat tube. Now don't get me wrong I am not saying don't do it or that for odd applications it may be warranted but for most applications it is not necessary.

 

[Fabian]

I agree with your assessment Ghost on any misalignment issues or bad installation masking problems, requiring a need for a tensioner.

I'm coming from a different viewpoint though: the point being convenience: set the engine in the frame and never have to bother with readjusting chain tension, as the tensioner keeps compensating for chain wear.
As a side consequence of installing the tensioner, a source of vibration coming from the chain was reduced.

As you said, and i do agree; a chain tensioner is not needed, but it makes things somewhat more convenient.

Fabian

 

[Ghost0]

One other thing to be mindful of when installing a tensioner is that it should not be a spring loaded tensioner. If it is and your chain still has too much slack when you try and start the engine it will tighten the tensioner side of the chain causes the backside to go slack which may cause chain derailment during the starting process. Just something to be mindful of.