Jackshaft Problem

MrLarkins

MrLarkins

HS Math Teacher
Yep, I'm back after a few years off.

I wiped the dust of the ol' motorbicycle today and decided to give it a whorl. I hadn't ridden it since I installed the jackshaft kit and had too many problem with a chain derailing. But today, I think I worked out the angles and actually took it for a spin around the block. At mile 1.5 , the front freewheel wasn't anymore. For some reason the motor turned the pedals and I couldn't stop it. I earned some scratches on my right knee from the force. So I am curious, what should I be looking at? Bearings? or something else?
 
I remember you...you got into MBs when I lived in Arkansas. I'm back in Colorado but do miss the warmer weather during the winter.

Here are some tips I've learned from building and riding shifter kit bikes.
1. Don't waste your time with stock freewheel hub. Get the heavy duty one from SBPs. The stock one lasts about 5 months than fails in the same way yours did. Heavy duty one hasn't yet.
2. I had many issues with chain jumping off the jackshaft. I now use a Sram chain and keep the tension very tight. Sram chain has very little stretch and the tight tension has allowed me to enjoy the shifter kit. The tight tension is very hard on the freewheel hub but the heavy duty one can handle it with no problems.
 
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MrLarkins said:
At mile 1.5 , the front freewheel wasn't anymore. For some reason the motor turned the pedals and I couldn't stop it.
Click to expand...
Since the right pedal crank connects directly to the freewheel and the sprockets to it the only thing it can be is the freewheel seized.

It is hard to help with anything without pics but I have built a few jackshafted bikes now with parts for another one on the way so I can share this with you.

1. If you are using derailer gears, especially one over 5 speeds or old, expect chain jump. As your chain moves down to the smaller sprockets it moves the angle of the chain out, and with the poor tension the pedal chain will slap the motor drive chain on the outer sprockets.

In short, a JS works best by far with internal hub gears in every way.

2. The freewheel bearing that is attached to both front sprockets rides on the right pedal crank to the BB shaft. If that BB shaft itself is loose, the sprockets cock-eyed, whatever, the freewheel will go first if not the whole BB assembly.

3. The 'Jump Stop' guard in the kit is not fluff, it has a purpose, which is to keep the pedal chain from jumping inside if it gets loose and or slapped by the the JS drive chain because it is loose.
Placing the Jump Stop 'just so' is not rocket science, but there is a proper way it needs to be installed to actually do it's job.

The trick is to get the JS shaft and gear itself aligned vertical best as possible for the outside sprocket as well as with the inner pedal chainring with the drive wheel.

I agree that SBP's new ver 2 HD kit is the one to buy, but even though I upgraded the 3 piece ver 1 mount to a ver 2 one piece I am still running the same BB and despite my best efforts to break it with power it is still as sweet as ever after nearly a year.

The bottom line is any loose or poorly aligned anything in a chain and sprocket setup will always be a problem that only gets worse.

Detailed Pics would help.
 
yea, the freewheel was the original setup, ie, not heavy duty...so Jim from SickBikeParts is sending me a HD setup...I'll post results after the swich.

Thanks!
 
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