Scout generator chain - tension varies !!

I think I opened the proverbal can of worms today ! I was re fitting the generator to the bike after a thorough overhaul and while setting the drive chain tension/play I noticed it go tight then over 1/2" of slack on turning the motor over. Could a knackered chain do this ? Generator sprocket appears to be running concentric and looks fairly new. Looks like a fair old strip down to check the crankshaft sprocket.
Just when I thought I was on the home straight
Regards
Paul

Hopefully it's an uneven worn sprocket on your crank and not the crank itself. Can you borrow a dial guage to check sprocket or crankpin runout?I've had sprockets rebanded before(not Indian stuff).

Paul
Check your generator sprocket, it will be the culprit. I am guessing it is an original sprocket as they are often eccentric. Set your 1/2" play at the tightest spot on the generator sprocket, then keep rotating the motor using he rear wheel to check and recheck (there will be chain slap at an idle). or re machine the taper for a proper fix.

Hamish