FIRST POST secondary shaft chain super loose and makes loud noises at idle

I have a 1983 KZ550 M1 and the secondary shaft chain is super loose, and there is wear on the teeth of the gears connecting the crankshaft to the secondary shaft.

what would be the best course of action to not have this problem? The odometer reading is 79K km with possible extra 100K km. bike runs fine above 2K rpm but makes a noise like nickels in a washing machine below 2K rpm. Previous owners had kept up with maintenance religiously. every other part of this engine appears to be in perfect condition, so the oil filer has clearly been doing its job.

To the best of my knowledge there isn't a "tensioner" for this chain, at that mileage I guess the chain is just worn out and requires replacement.

The clutch basket uses rubber bumpers to absorb shock, and it's quite common for these bumpers to shrink with mileage, increasing lash in the system.  Between a loose basket and worn chain, noise will develop.