Hi Nick I have used high grade aluminium for all sorts of wear parts from motorcycle disk brakes to plastic mould tools but they were all hard anodised and some were PTFE coated, not cheap but very light and wears well.

David

Problem with aluminiums is its picks up at no notice. Rotational will wear quick.

Intrigued by aluminium discs Dave, have had hard anodising and ptfe impregnated stuff done but were slow moving parts.

"The probem is that small particles of aluminium wear off and oxidise. Aluminium oxide is used to make grinding wheels.

Brian"

If this is the case, how come most IC engines are running with Aluminium pistons.

I see no problem with using Aluminium alloy for eccentrics, provided eccentric straps are made from case hardened steel. However, the environment beneath a Locomotive boiler is hardly conducive to longevity of nearing surfaces.

Many small engines use aluminum alloy rods running directly on a steel or cast iron crank, and aluminum pistons in the bores. However, these engines are closed crankcase designs and have a generous splash or pressure feed oil lubrication system, not exposed to dirt ash and grit generally. In addition the aluminum used is a special high silicon die casting alloy not generally available in bar form.

As Bob said the underside of the locomotive is not particularly free of dirt ash and grit. Oil supply to the eccentric is not a sure thing.

I would say any benefit of using aluminum in this case is negligible and there are some risks, I would also recommend the traditional steel/bronze or steel/ cast iron combination for eccentrics on locomotives. They are well proven in small and large locomotive bearing applications.

S.o.D: The rings need to be free in their grooves to work, and this means not constrained by having to act as location for the piston. (Which would mean that the back of the ring was in contact with the bottom of the groove, stopping the ring from moving freely). The aluminium doesn't touch the cylinder very often or very hard because there is a film of nice grit-free oil. Or did I misunderstand your meaning?

Bob R: Most engines (certainly those with aluminium pistons) run with their pistons in a spray of oil which is filtered and renewed. They are not in an atmosphere of ballast dust or ash. And the aluminium is indeed a fancy high-silicon alloy not easy to get even if you do want to make eccentrics out of it.

Cheers, Tim

Edited By Tim Stevens on 25/08/2018 18:42:55

If you must use aluminium for an eccentric strap, the crown of an old (reasonably large) piston (old truck, or tractor) would supply enough metal. If possible, use cast iron, much lower friction, and with a locomotive the usual thing is to try and get as much weight as you can for traction, there is nothing gained if you save a few grams in one place, and add blocks of lead for extra traction.

Ian S C