Mark lll Rear Sprocket

My new 42 tooth sprocket for my Mark lll does not lie flat against the cush hub.

At issue is the shallow inset on the back of the sprocket thus not allowing the cush hub lock nut to properly seat against the sprocket.

My solution will likely be to machine the back of the sprocket to fix it.

Has anyone seen this before, and am I on the right track?
Thanks!
Stephen

I think there is supposed to be a small gap between the sprocket and the cush hub. At least that's what I was told when I mentioned mine was the same as yours.

Here is a pic of mine

To clarify, the old rear sprocket does lie flat against the cush hub, hence my question to the group.

It has a deeper inset on the back.

That said, I wonder why the possibly improper inset on the new one?? Would it be offshore vs. UK manufacture?

Or, could it be to make sure there is a gap?
Stephen

The sprocket shown below is 11+ years old. The sprocket vanes certainly appear to fully engage with the 066232 "drive centre" slots.

Mine also has the gap, if you think how this works metal to metal contact would not be good and you would soon see aluminium swarf as the two surfaces move relative to each other as the drive is taken up. Though it may seem strange to see the gap, it is good providing the wheel is fitted correctly as the spacing is determined along the wheel axis bolt when correctly tightened into the cush drive side.

Thanks All, and sorry for more questions.

I can see it makes sense to have a small gap. But, I wonder why the original sprocket seemed to have a zero to small gap?

The other issue I did not mention clearly is that the back of the sprocket seems to rest upon the lockring, causing a very wobbly feel. It also caused the chain to be out of line with the sprocket.

It seems to me the lockring needs to fit enough into the back of the sprocket to avoid it being the contact point. I understand that the ONLY contact should be the sprocket splines into the cush drive rubbers.

Thanks for the photos. I hope L.A.B. did not dis-assemble just for this explanation! If you did, thank you for going over the top!!
Stephen

chasesa said:

I can see it makes sense to have a small gap. But, I wonder why the original sprocket seemed to have a zero to small gap?

The other issue I did not mention clearly is that the back of the sprocket seems to rest upon the lockring, causing a very wobbly feel. It also caused the chain to be out of line with the sprocket.

It seems to me the lockring needs to fit enough into the back of the sprocket to avoid it being the contact point. I understand that the ONLY contact should be the sprocket splines into the cush drive rubbers.

Click to expand...

"New" sprocket, of unknown age-but not recently manufactured.

chasesa said:

I hope L.A.B. did not dis-assemble just for this explanation!

Click to expand...

No-it wasn't necessary this time! :wink:

I machined a bit off the spacer many years ago to reduce the gap and replaced the sprocket last year without any issues.

I hope this helps ?

Cash

I've got a new (it looks like recent production) Andover sprocket waiting to be fitted. It has a chemical black finish rather than paint.

L.A.B.'s measurement of .130" from flange to inside recess ties in with mine as well.

I suppose that I should get round to swapping over and checking the difference.

I machined the rear sprocket in the lathe yesterday according to L.A.B.s figures.

Two changes were necessary. First, to true-up the splines so they are each the parallel and the same height from the "flats" that rest against the cush hub drive centre. In doing this, I had to ensure the splines "height" was less than the depth of each of the 5 drive slots. They weren't, but they are now.

Secondly, in order to clear the lock ring in the centre (.090 high) I had to machine the centre of the sprocket by around .100 to obtain .125 (not .130, not needed).

That done the sprocket now lies flat against the cush hub drive centre and all should be fine.

Not sure how I got into this, but I am betting the sprocket was offshore manufacture. In any case, it's now better than OK.

Thanks L.A.B & gang!
Stephen