Forum

[NicoV]

In the gearbox there is a brass bushing. Why is it brass ? I thought brass was a weak metal that easily wears out.....

[Dennis C]

Brass work hardens and is far tougher than people think, however it is more likely to be phosphor bronze.

[PeteF]

Bronze makes a very good bearing surface for the steel shaft that runs in it. Eventually it will wear and be replaced but the shaft will not so you just replace the cheap bit. This is the same theory as white metal bearings and old babbit bearings. The bearing surface is made of softer metal so it wears rather than the shaft. Of course, this only works if everything is kept lubricated.
Interestingly, it's the same theory as making gearwheel teeth in windmills out of timber. They are the bits that wear out (or break) but are easily and cheaply replaced and by relatively unskilled workers.

[neddy]

Brass can be better than Phosphur bronze in some circumstances as bearing material

[jefrs]

Having had to hacksaw through a 3-in bar of naval brass (which is technically bronze) I can assure you that brass (or bronze) is a very hard material. Brass is copper/zinc, bronze is copper/tin, naval brass is copper/tin/zinc with a little lead; phosphor-bronze obviously includes phosphorous, both lead and phosphorous in the alloys can act as self-lubricant.

Regarding white metal bearings, these are usually fabricated with hard and soft material so that the softer metal gouges out to provide 'natural' oil-ways, and the bearing deforms to provide a perfect fit to the shaft; so there is some method to the old madness.

[p]

My experience of old engines was that, so long as they didn't run short of oil, the crank pins wore more than the white metal bearings; my understanding at the time was that microscopic abrasive contaminants would embed themselves in the softer material whilst abrading the harder one. Certainly in memory, unless a bearing "ran", there was little gain in renewing shells (or re-metalling bearings) without attention to the crankshaft.
Sorry, not really relevant to the op's question about yellow metal bushes!

[nickbarber]

A bronze bush is used with a steel shaft. It is obviously softer so it does not mark/wear out the steel, rather it does the opposite. so if/when the bronze bush is worn, it is cheap to replace, instead of the expensive steel shaft ie, crankshaft, camshaft, etc etc

[papasmurf]

Look what happened to Fred Dibnah's traction engine front wheel bearings that he made from "some unknown stuff from the breaker's yard".
Brass is no good as a bearing.

[NicoV]

Thanks to everyone for the replies. Very interesting to read. I really didn't know