[Joe K]

Elsewhere I have described the issue of both aluminum fan hubs (the hole was done as an "as cast" form and tend to "wasp waisted" reverse barrel shape) and the pump shafts (many shafts were provided with an actual "barrel shape" as in two different tapers.)

Its all a matter of "quality."

The issue(s) are overcome somewhat by repeated tightening which "stretches" the aluminum hub over the barrel shaped taper, galling the aluminum and possibly the shaft. In effect what one achieves by repeated tightening is what the machinists call an "interference fit." Hence the difficulty of removal. While a locking type material MAY have been used, it likely was not, and the interference would force it out if it were.

It's not like a "real" fit in this case where the aluminum hub stretches uniformly over the uniformly tapered shaft. Instead you tend to get "point contact." (line contact?)

The use of a washer compensates somewhat for the point (or line) contact thus formed, and the washer gives you some freedom of motion for additional tightening without bottoming out the nut.

The later shafts and hubs are better - more uniform in taper and a step up in quality - but I'm considering the issue is far from solved.

Joe K