Assuming the correct spring was used when my boxer was rebuilt
how much should the belt move by when I press it with my thumb more or less.
As i know these springs can't be ordered anymore, and they are not part of the
belt tensioner or the complete cambelt+tensioner set either.
Probably you still have the factory ones.
The force of the tensioner spring in my '92 and '94 33s is not enough anymore to set
the necessary belt tension by itself. I have tested springs from a '96 146 1.6 boxer,
but those was weak too, i have to "override" the spring loaded belt tension while i was
tightened the nuts.
(Just a note: in many cases there's no need to replace the tensioner arm,
just the caster. Some cash can be saved because you can get a caster with
SKF bearing about half of the price of the complete tensioner arm.
But i agree, it's much easier to replace the whole tensioner.)