Difference in front drive sprocket thickness causes rubbing on inner primary case

[jimbo]

After getting the MK3 engine in the frame, I am starting the primary assembly. I had rubbing from the sprocket and rebuilt the transmission because the sleeve gear bearing fit was loose. I still have rubbing with a different trans case and the 21 th sprocket I used before. I compared a 20 tooth I have with the thickness of the 21 tooth and found the 21 toother is much thicker causing rubbing and maybe a chain misalignment. Confused again......

 

[concours]

I would call that “hub offset”, based on the side view.

 

[Craig]

Pretty sure I have 22T and 19T sprockets in shed , do want thickness measurements , the 21T is on bike ....

 

[jimbo]

As the 20 thoother fits with no rubbing I think I'll go with the 20 , as we don't run on the interstate much any more, and the bike was real happy at 65+mph but not at 55 , so I'll drop the happiness down to about 60 +. Its a big mystery , they only thing I can think of is the sleeve gear and bearing moved away from the inner primary cover enough to allow me to ride it for years that way, because the bearing fit was loose. Now that I have the bearing tight in another case it rubs more.

 

[L.A.B.]

The sprocket on the left in the 1st photo looks like a typical AMC/Commando item.
https://andover-norton.co.uk/en/shop-details/15387


The sprocket on the right could be for an earlier gearbox?
https://andover-norton.co.uk/en/shop-details/18446

 

[justin scroope]

Had this problem back in the eighties. Turned out that the rubbing sprocket was mean,t for a featherbed.

 

[jimbo]

Had this problem back in the eighties. Turned out that the rubbing sprocket was mean,t for a featherbed.

funny thing is , I ran it for years on the MK3,when I removed the inner primary it showed rubbing, but not so much and I never noticed a resistance or noise.But it rubbed big time when I rebuilt the trans. So I am thinking the looseness in the old trans sleeve bearing fit allowed it to move away from the inner primary cover and the drive chain just ran where it wanted moving the sprocket away.Keeping it from rubbing. Kind of weird .