Originally Posted by Roelof

Indeed, you would say when pinching you do create space between sleeve and crankcase which can be filled up by expansion. But the expansion is not determed by the amount of space but only by the specification of the material.

Pinching is actually deforming the material by squeezing it together to a smaller diameter but the expansion rate will be the same.

Yes, there is a kind of memory that the material wants to go back to the original shape, when doing a small pinch just as much that the piston fits right can be easily pushed back. You must see it as a piece of piano wire, you can bend it a bit and it will return to its original shape. Bending it further there comes a moment it will stay on an angle but again you did have to bend it further to get this mall angle as end result and in use there is a chance that it will go back a tiny bit to the original shape.

With pinching you can see that, With a tight pinch some sleeves do not need a long running in to get rid of the tight pinch. That spring effect together with the force of the piston is shaping back the sleeve a bit.

It seems the harder the sleeve the less spring effect there is.