Annoying wobble

jspbtown

Active Member
#1
!970 Rupp Scramber...10" wheels

What would cause a slight wobble in the sprocket that causes the chain to loosen and tighten as it rotates. Used a marker, laying on the swingarm and rotated the wheel, and got about a 6" line (it got closer to the swingarm) on the sprocket. I can see the slightest of wobbles but I had no idea it needed to be so true.

Plus how the chain gets tight and then loose, and then tight again as it rotates is causing me a brain fart.

Thought maybe a bent rim so I swapped the front and the rear and it does the same thing.

Bent sprocket? It seemed to lay flat when I had it off. Thoughts?

Thank you
 

jspbtown

Active Member
#3
Chain is brand new. Any way I could tell if it was "bad" from the supplier?

And "screwed up teeth"? Would that be possible to see somehow? The teeth look fine. One had a little lip which I filed slightly.
 

pomfish

Well-Known Member
#4
how tight do you have the chain also?
Have had bikes that do the same it is annoying for sure. Too tight they bind too loose they derail.
Possible the engine plate is not on an even plane compared to sprocket

If chain is new it probably is good. Side to side friction from warpage can cause binding as well.
Different brands of chain seem to have better spacing as well.
Gotta remember these sprockets we buy are not exactly high precision and in some cases are made on old worn equipment.

Anyone old timer here will tell you the real old Azuza wheels were a whole lot better than the stuff of the last decade for an example.
Best of luck
 

jspbtown

Active Member
#5
I have the chain pretty tight. I rotated the wheel until the chain was on the "loose" side of the rotation and then tightened it so it does seem to have a little bind at the "tight" part of the rotation.

Sprocket is not attached to the engine. It is attached to a stationary jackshaft. Bdone1.jpg done3.jpg
 

jspbtown

Active Member
#8
Hmmm...Interesting. Thanks guys.

When I looked at the sprocket that Black Widow is offering I see that it has 6 mounting holes. But when I look at my sprocket the mounting "holes" are actually shaped like a U. I have no idea why, but I guess that could be the reason for it being off centered on the hub by a little right?

The hub is a very good fit (bolt hole wise) on the rim...and as I said I tried both rims. None of the holes are wallowed out at all and the bolts fit perfectly and are snug.

I appreciate the help. I just don't want to fire up the parts cannon without putting some thought around it
 

mustangfrank

Well-Known Member
#9
Hmmm...Interesting. Thanks guys.

When I looked at the sprocket that Black Widow is offering I see that it has 6 mounting holes. But when I look at my sprocket the mounting "holes" are actually shaped like a U. I have no idea why, but I guess that could be the reason for it being off centered on the hub by a little right?

The hub is a very good fit (bolt hole wise) on the rim...and as I said I tried both rims. None of the holes are wallowed out at all and the bolts fit perfectly and are snug.

I appreciate the help. I just don't want to fire up the parts cannon without putting some thought around it
The sprocket is an easy check, measure from the hub flange to the teeth at several points around.
 
#10
Will do. Any thoughts as to what type of variance would make an impact? Just by looking at the back of the junction between the hub and the U shaped holes on the sprocket it looks pretty close.

Also.....do you think its possible the sprocket is warped as there is the wobble which was not improved by swapping the wheels. But would that cause the tightening and loosing of the chain as the wheel rotates?
 

mustangfrank

Well-Known Member
#11
Either could cause it...warped could but it seems like it'd have to be really bad. Wouldn't take much sprocket off-center to change tension. Assuming this is new or smooth running chain?
 
#12
Yes, brand new #35 chain. It is running very smoothly on the motor to jackshaft side of the engine.

The wobble is very slight...and as you look down the chain you can see the chain aim a little left, then come back to center. As I said..if I take a marker and lay it on the swingarm and start the motor and let the wheel spin I can slowly bring the marker in until I have contact and it will create about a 6" line on the sprocket itself.

I thought maybe a bent wheel so I swapped the front to the back and got the same result in the same spot. So that leaves me with the sprocket or the hub I guess right?
 

DaddyJohn

Well-Known Member
#13
I have the chain pretty tight. I rotated the wheel until the chain was on the "loose" side of the rotation and then tightened it so it does seem to have a little bind at the "tight" part of the rotation.
You want to adjust your chain at it's tightest spot, rather than the loosest.

This may or may not be the solution to your problem, but it is how chain adjustments should be done in general...

Otherwise, it could be possible that you got a new bad chain. Not particularly likely, but possible.
 

Doc1976

Active Member
#14
This is a very common problem. As said already, the hub and the sprocket are not concentric. I explained in pretty good detail how to remedy this in another post a while back. Let me see if I can find it and I'll post a link.
 
#17
I appreciate the links. Decided to pick up a new sprocket as I wanted to get some rear adjuster washers anyways. If it gets above 0 degrees this weekend I might venture out!

As a side note... I just want to say that BlackWidowMotorsports.net is a great vendor for parts. Really fast shipping and some really good stuff.
 
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