Jackshaft Swing arm relatinship

FOMOGO

FOMOGO

#1
#1
I am trying to figure out what is the best way to run a swing arm and the jackshaft in one mount. Along the way the Bonanza mounts work/look that OldMiniBikes sells. Is there a rule of thumb for the 2 points being to far away from one another? Or do they need to be as close as possible?

I fell like I am being a pain asking all these JS questions but this is my first attempt at this and I appreciate the knowledge base here at OldMiniBikes. Most of you have forgotten more than the little bit I know about minibikes...

So thanks for your input and your time.

Doug
 
H

Havasu Dave

Moderator
#2
#2
As close as possible so that the chain doesn't go loose and tight with swing arm movement. I recall a Taco 99 I had and that distance was around two inches.

There were many bikes produced which used an integral swing arm and jack shaft. Other members know, I forget stuff like that. If you go that route, your swing arm bushings need to be bearings, since bronze and the like wont stand up to JS rotation.

No rule of thumb though, since the effects on the drive chain are predicated by the length of the chain and the moment of angle. The chain will serve as an anti-squat device and limit your travel if your shock absorbers don't.
 
FirePowerMinis

FirePowerMinis

Active Member
#3
#3
MX bikes went through a chain-tossing era when travel doubled in the mid-70s.
Before, being in-line was enough, and on a short-travel mini, likely still is.
But, it should be pretty easy to incorporate JS and swingarm pivot.
 
P

PAP

Member
#5
#5
It will depend on the amount of movement and the length of the swing arm, but in most cases the swing arm on a mini is only 2-3 inches of travel at the axle. The pivot point should be on the same centerline as a straight line drawn between the center of the jack shaft and the center of the axle. Keep the distance between the jack shaft and the pivot point to 2" or less. If you draw out the arcs, you'll find that the distance changes very little with swing arm travel. For instance, with a 12" swing arm arc, and a 14" jack shaft arc, the amount of chain slack is .052" at 3 " of upward travel. The longer the swing arm arc, the less the slack.
Some of the early Taco 44's had a jack shaft swing arm, and it proved to be problematic, so the they went with a separate pivot.
 
125ccCrazy

125ccCrazy

Well-Known Member
#6
#6
I built a custom swingarm for a bike my son had, I put bearings in the swingarm and used the pivot shaft as the jackshaft..this set up worked great...no more chain tightening or loosening when the shock was compressed.. If a set up like this isn't an option do as PAP said above and keep the centerline between the jackshaft and swingarm pivot shaft on the parallel.
 
yankee-bears

yankee-bears

Member
#8
#8
Bird Mfg. had a good idea when they designed the roper series mini bikes . They had the whole motor plate pivot . Makes a really good rider without the chain problems .
 
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