The major difference between aluminium and lead based bearings is the way
the material is applied to the backing. (This is basically the difference
between original Vandervall as specified by Triumph and cheaper aftermarket
Glacier never fitted or sold by Triumph) The lead based bearings have the
materail cast on, the aluminium type as done by sintering whereby an
aluminium based powder is pressed and then the whole thing heated to fuse it
all together. The result of this is that under extreme pressures the powder
type will tend to strip off as the bonding to the steel backing is nothing
like as strong, so for hard use (ie high revs) the cast type are essential.
For normal driving conditions it doesn't matter too much, and the softer
ones are more forgiving off bits of rubbish going round after an initial
build. However the ally ones are usless as thrust washers and shouldn't be
used under any circumstances (not for the rear one, front one doesn't
matter).
A fairly modern example of the differences between bearings, is in the ones
fitted to Ford Escorts in the UK - Ford, who aren't exactly noted for over
engineering anything, used Vandervalls in the turbocharged versions of the
engines knowing full well that aluminium ones would fail even within Fords
parsimonious warranty period.
John Kipping
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