Originally Posted by Billy22Bob

So I'm trying to understand...forgive me if I'm a little slow on the uptake.
What is the cause of failure?....heat?
Why is heat a problem? Because it can make the backing plate brittle?
Where is the heat being generated from? Sliding on the magnet?
Why is it sliding? Too much gap?
Why is there too much gap? 1) Rivets not recessed?, 2) incorrect shims/setup?
What evidence is there that heat/sliding is a problem? - Burnishing on the rivets and backing plate (ultimately)

Please fill in any missing or wrong details/statements. And we'll come to a consensus.

Another thought....
Trying to understand the pulley itself......

When the magnet engages - the backing plate gets magnetized and lock step with the main magnet/rotors.
Of course the backing plate can't move - so this locking is purely magnetic...or is there movement and you get friction "grip"?
Now - all the force/resistance provided by the rotors in compressing the air - is fed back through the pulley to the belt.
This is transferred through the rivets and the attached arms....into the pulley.
The force required to pump at 74mm pulley is much less than a 65 or a 62mm pulley. We are talking something like a change from 25 to maybe 45-55kW of required energy in the Sc.
So - is this increase accounted for in the design? - is it reaching the limit of the material strength?...
Is all this I've said bull$hit?