Chain gets loose and then tight when rotating. Some specifics too...

GoldenMotor.com

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
1,211
113
CA
Chain gets loose and then tight when rotating. Some specifics too...

The tight and slack were simultaneously observed on both sides of the chain going to and from the sprockets on the two jackshafts. I checked to see that the alignment between the two gears were correct and the chain was centered on the teeth. I found it OK.

There are two jackshafts I have for a huge lowering ratio I want to achieve. I still use two belts with pulleys but they are not giving any problem. There was a belt between two pulleys and one was very small diameter 1.7 inch. I had slipping so I went with chain instead.

Before I got a 28 tooth sprocket that I was waiting to be mailed to me I used two 18 tooth sprockets. There would be no assistance in lowering the ratio with that but I wanted to see how it would work.

It had no problem other than I was only getting a 14:1 ratio from the pulleys and belts and I wanted more for off road trail and hill climbing. I also intend to have slow speeds under 5mph with out having to pulse the throttle for parade events.

Then I got the 28 tooth sprocket and the 18 tooth sprocket with a new chain on the two 5/8 inch diameter jackshafts with keys installed. This now added to my lowering ratio. 14 * 1.5 = 21:1 ratio.

I heard the chain making a sound and found it got tighter and looser as it turned. I was only turning it by hand. I would not trust running the engine with it this way.

Just to see I went back and set up the two 18 tooth sprockets and I noticed it did the same but very slightly. Nothing looked out of round on the sprockets, but I noticed it got the chain the most tight only when the keyways were opposite facing away from one another. Also visa/versa, when the keyways in the two jackshafts where closest adjacent to one another the chain slackened the most.

This would have me believe that the sprockets even though not out of round are not centered on the jackshaft exactly. The set screw pushes on the key into the jackshaft’s keyway. This then I think makes the side of the sprocket with the set screw, by the keyway, move a slight amount away from the center of the jackshaft. This essentially makes it an effective out of round. It could only happen if the fit of the sprocket was loose on the jackshaft.

With the two 18 tooth sprockets having this tightening and loosening effect, it was not anywhere as pronounced as with the 28 tooth sprocket and the 18 tooth sprocket. I had to fix this as I would no way be starting the engine and running it like this.

I noticed that my new 28 tooth sprocket fit tighter, so I think it is not the problem. I have a new chain, but will eventually set up with using the same older chain that did not have as much problem when used with the two 18 tooth sprockets.

Further I have bought two new jackshafts and got a newer 18 tooth gear also, so I’ll be giving it a try later.

I wondered if some brand new chain that looks fine and is lubed and nice and flexible could accentuate the effect of the keyway and off centering. This maybe if the links were not exact to standard of a #35 chain.

The 28th tooth sprocket and the older 18 tooth sprocket together have that thing about the keyways facing one another or opposite one another; I wish to know if this has ever been observed before by anyone.

With the two new jackshafts I hopefully eliminate the possibly of bent jackshafts. It should mean the newer 18 tooth gear and the 28 tooth gear being better centered in relation to the jackshaft.

I'll know in the next couple of days when I can get back to trying the new parts and see if the problem is solved. Then to see what 22:1 with a 3hp Briggs can climb.

MT

http://motorbicycling.com/showthread.php?p=528756#post528756
 
Last edited:

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
1,211
113
CA
I just thought of what I have done before with centering drive pulley on my rear wheel spokes. Some one else also mentioned to see if a sprocket were not true by doing this test. I will clamp my t-square ruler to the side bracket of the part that holds the jackshafts. Then adjust it far enough away from the sprocket as I turn it and it does not hit the ruler. I'd then see if the gap varies to any degree. I could check side to side wobble and out of round on both with the chain off.

I'll do this before trying the new parts so I may get an idea what is acceptable and works.

MT
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
for things that fit loosely on a shaft, I've taken an old feeler gauge and cut off a bit to use as a shim
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
1,211
113
CA
Thanks for reminding me of that.

I have some very thin brass sheet that I can use. It may be what I may use if otherwise it does not get fixed. I just have to make a cut away for the key way.

MT
 

racie35

Active Member
Nov 17, 2012
1,702
5
38
usa
to go from tight to loose the keyway wont be the problem....you could pull it and spin the thing and the problem will probably be there still.....sounds like an off center bore issue or bent shaft the sprockets on.
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
1,211
113
CA
http://motorbicycling.com/showthread.php?p=528756#post528756

See top of page at my thread: "
Art Fish Mobile Motor Bike prior Motor Bike DIY'er build to add side car maybe?"
page 15 at post 141 third picture.

Those are the two 18 tooth sprockets that only cause very minor tightening and loosening, but they are like I mentioned loose when keyways of the two jackshafts facing one another and tighter when facing away from one another.

I think that since when I use the 28 tooth gear with an 18 tooth gear and it does a lot more loosening and tightening in comparison, I know that it is that the chain length is shorter. This means you would naturally get the looser more loose and tighter more tight because there is less length of chain. I guess that is why I can get away with the two 18 tooth gears as the chain length is longer.

I will post more pictures, but I have to get time again to be working on it.

I will lay to the two old jackshafts out on a flat surface and roll and see if bent. The two new ones as well.

MT
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
22
0
memphis Tn
Can you rotate one shaft 180 deg to keep the offset consistent? It would travel in a small oval, but if they line up right, it should stay tight while wobbling, so to speak.
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
1,211
113
CA
Can you rotate one shaft 180 deg to keep the offset consistent? It would travel in a small oval, but if they line up right, it should stay tight while wobbling, so to speak.
I thought of that. Its like two wrongs make a right. Only that when I use two of the same size gears it stays in sync, ie the two 18 tooth gears that worked OK.

When I use the 28 tooth gear and the 18 tooth gear it takes a while but eventually the keyways will be both opposite or adjacent. They at best would be somewhere in between for a while, but when it gets too tight or loose and risk of chain snap, bend link, or what ever not so good stuff to happen, I can't risk that.

If they could stay 90 degrees off that would be best. That is how I would do it when there are two of the same size gears as it can work that way. I could use other pulleys on my first driven pulley and make it smaller for higher ratio, like land speed record (less than 14:1 ratio) on desert flats.

But for lower ratio I am already using the 1st drive pulley of about 10 inches diameter and the rear wheel drive pulley is also the same about 10 inches in diameter.

I crammed a bunch of gears and pulleys just behind the seat post tube at the back of the engine platform and when using pulley and belts there was not a problem as they stretch and retract again.

The problem is that a small pulley at 1.7 inch just can't take the load without slipping. 3hp of the Briggs 4 stroke did actually hop the front wheel when I gassed it from idle before.

When I get this working with no slip by switching to gears and fix the tightening / slackening issue maybe wheelies!

I though am going to get the 28 tooth gear to work, but time to work outside is limited by daylight. Next chance I get, but working into the morning hours outside is going to be chilly. I don't mind the 50's but they say high 20's for a few days here in CA. Gonna cover the orange tree and use a 25 watt incandescent bulb.

MT

PS:

Thanks and I wish I could use all your ideas right away, but I really don't have any inside space to work, so it may be some time. Thanks though all the responses!

Some attached pics from last outing. The rusted iron, not my bike, although until painted yea it too, I found looks like farm equipment on the side of the trail. Not moonshine still stuff, but antique I would bet. Fun to explore!
 

Attachments

Last edited:

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
1,211
113
CA
I found the problem not to be of any worn or broken part, but was alignment not done very exacting. The two jack shafts have to be parallel. I had used 4 shims before when I adjusted the bottom jack shaft to align with the top immovable jack shaft.

I had not created new ones and spent some time seeing that they were parallel, but obviously not enough time. That is why I made the shims before so it would not have to be figured out each time.

Anyway I did get a new bottom jack shaft in place and I checked the new chain for how much and arc it had when it resisted bending side ways as part of the test.

It turns out the old chain I found being thrown out (made in USA), had half the amount of distance in the middle of the arc in relation to a straight chain, than the new chain. New chain supposedly not the best then.

I used the new chain anyway and soon when I won't wake people up, I can be starting the engine I can test it for real riding it.

I also checked the revolutions of the bell on the centrifugal clutch for the valve on the rear wheel to go around once. It was 22 times. I expect this should climb the hills a bit better than the 14:1 ratio.

I also tapped the end of the top jack shaft and used a 1/4-20 bolt, washer, and lock washer to add to holding the 1st driven 10 inch pulley on better. I also sandwiched it on the other side with a split collar.

Later when I get a chance I will need to take the engine off the frame to get access to putting in a new recoil cord. I will also get access to the back idler pulley that I want to shim. I want it to be better centered on the belt going from the centrifugal clutch to the first driven pulley.

MT
 

Attachments

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
1,211
113
CA
I have not yet has a chance to test ride the bike yet.

I think I know why I thought the keyways of the two jackshafts when facing each other or away from one another had something that coincided with the chain getting tight or loosened respectively.

When I put the chain master link on I put it by links that were just near a sprockets teeth near the keyway. I did this just as a coincidence. I found it easier to put the master link clip in place when it was on teeth of a sprocket. That is rather than in between sprockets where the chain would move making it harder to do.

I can tell the master link will tend to bind more than any other area of the chain on the sprocket teeth if the chain is at an angle between the two sprockets.

Since I did not at first have the bottom adjustable jackshaft exactly parallel to the top jackshaft, there was this angle causing a bind as was it turned.

The chain tries to climb the edge of the teeth when not aligned right.

I found this and to be and as a test I corrected it at first temporarily by pushing the chain on one side to try to keep it in line while I rotated the chain. When I did this it did not catch. Since it worked I went back to making the bottom jackshaft more in alignment with the top jackshaft.

Additionally I put a washer to shim one of the sprocket sideways so I was more in line with the other sprocket.

In any case tightening and loosening and catching sprocket teeth on links of the chain on the side inside edge stopped all together when I got the two jackshaft parallel to a more perfect degree.

MT
 

Attachments

Last edited: