tricky drive chain adjustment

With both rear axels loose, I adjusted chain to 1 ¼” slack. After I tighten timing side axel, somehow the chain tension has been changed to 5/8” slack. While tightening timing side nut there is no movement of axel relative to swing arm but there is movement of the rear sprocket relative to swing arm. Both were checked with dial indicator.

Does anyone have any ideas on what could cause this?

I moved axel in 2 flats and now get ¾’ slack when tight. Uniform around the chain rotation, so it is within spec, but this is not how my other Commandos behave.
1973 750.

Possibly the swing arm has a slight bend in the axle plate area so one tab is bent in or out so when tightened, the axle is trying to go 90 degrees to the tab.
Another possibility is that the axle is not really straight in the frame no matter how careful you are and again, the axle is looking for 90 degrees to the axle plate.
The way I align the wheel and axle is to use a pair of old time 10" or 12" dividers and find the distance from the axle to the swing arm pivot or the rear isolastic bolt. All three should be parallel. Find one side then match the other. The wheel will be very straight in the frame. Works on every bike. Norton is a bit awkward but doable. I found a set of dividers on ebay for $30. Well worth the price..."STARRETT 12" DIVIDER - FIRM JOINT - GREAT CONDITION" Take a look, this is the right type of divider. Maybe you can find it cheaper elsewhere....they want $15 for shipping. I was lucky to find a pair in a yard sale.

NickZ said:

With both rear axels loose, I adjusted chain to 1 ¼” slack. After I tighten timing side axel, somehow the chain tension has been changed to 5/8” slack. While tightening timing side nut there is no movement of axel relative to swing arm but there is movement of the rear sprocket relative to swing arm. Both were checked with dial indicator.

Does anyone have any ideas on what could cause this?

I moved axel in 2 flats and now get ¾’ slack when tight. Uniform around the chain rotation, so it is within spec, but this is not how my other Commandos behave.
1973 750.

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I usualy have trouble keeping the axle where I adjusted it when torquing the axle nuts. What seems to work best is getting the nuts slightly tightened, then using a rubber mallet to knock the axle forward against the adjuster bolts, then tweaking the axle nuts a little more, re-knocking axles forward, repeat until fully torqued to the 45-50 ft-lbs recommend value, not the workshop 70 ft-lbs (that will squash the speedo drive casing).
Also, be sure you are measuring chain slack with rear suspension supporting bike weight plus rider weight. One trick is to rig a bit of wire or string around chain up to seat, then see how much slack is pulled up while sitting on bike.

Of course you can also set slack bike on CS, by increasing the slack required to I think 1 1/4", vs 3/4" for compressed suspension.

do not tighten the right timeing first the left drum drake dummy axel must be tightend first or you will damage the wheel bearings