it's part of the chainguard extension mounting assembly - https://andover-norton.co.uk/en/shop-drawing/137/swinging-arm-suspension-units-chainguardCan I ask what that compression spring is for pinched between the guard side plates....
Thanks Bill. This sounds like the right approach. Get the sprockets aligned first as that is the most critical item. Then figue out a way to get the chain guard clearance without moving the sprockets. Any good tips tools or methods for checking the alignment of the sprockets?The alignment of the 2 final drive sprockets should be the prime consideration; this can be checked with a string or any number of laser projection tools which are inexpensive and readily available or suitable straight edge types of stock. You do not have to install the wheel, but if not you will need sufficient spacers to simulate the width of the hub, speedo drive, yada, yada.
When you are satisfied with the sprocket alignment you can install the chain guard and see how much clearance you have with the rear sprocket. If you find it too far off center you can, as Concours mentioned, do some bending which can be very satisfying especially if you don't ruin the guard. I have found that there is some wiggle room to be had by tweaking the front guard fixing bolt with the oiler/spacer fastener slack. If the guard is tight to the chain run to the right a washer/spacer can be placed between the shock mount and the "slotted cage" the rear guard mounting bolt slips into. If you use this solution be sure to use, and shape, a larger enough washer/shim to give the "slotted cage" sufficient contact/support such that it doesn't vibrate and tear.
Unlikely I would think as not only is the pre-71 a bolt-up drum with a different dummy axle assembly but because the 71-on drum assembly includes a (double-row) ball bearing and the pre-'71 doesn't.One other thing, the sprocket/drum assembly part number for a 1970 versus that for a 74 are different. Maybe the prior owner swapped out sprocket/drum not realizing (and they have different dimensions)?