Originally Posted by polyspheric
If the coil just pushes against a flat surface, one end or both will try to rotate as the spring compresses, but not smoothly (unless it's greased!).
The bearing assures smooth rotation so momentary binding will not give you a false picture.


Never really thought about that, haven't read about it or being discussed here.

But ir sure makes me wonder about the ramifications on valve springs, and in difference to OP and staying OT, i will not go farther, but would like to. work


Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.