Plain Bearing materials

[Mike Rometer]

Due to local domesticity I've been forced out of the w/shop, so work on the Twin is all but static. However I did find time to peruse the original drawings and noted that the material specified for the valve quadrant end bushes is something I hadn't come across before, "Iglidur", basically it's a self lubing plastic that comes in various grades but from what I've read seems to me to be completely over the top for this application. I'd have gone with gun-metal or P/bronze, or possibly PTFE. Self-lube is nice but I hadn't thought of these as a high wear point.

Has anyone else come across this stuff, and what have they found with it?

[RGSP]

I have come across it, and it's very good in a CLEAN environment. PTFE is generally a disaster in any application where there are metallic and other particulates floating about, because these embed into the plastic and can produce a very abrasive surface quite quickly. Iglidur is better, for reasons I've never been into, but I would still avoid it in a working steam engine.

Personally I'm very fond of sintered phosphor bronze, oil impregnated, but getting it to size with the bearing surface perfect needs a lot of care.

[Mike Rometer]

I've always found with sintered bushes it's best to stick with stock sizes, It does machine, but not too well, though it does ream Ok as long as the reamer is sharp. Always soak in oil overnight before fitting.

I've been reading around and found that PEEK is very similar to Iglidur in a lot of respects.

I can get PEEK and PTFE with various fillers locally.

[cyberbadger]

Personally I'm very fond of sintered phosphor bronze, oil impregnated, but getting it to size with the bearing surface perfect needs a lot of care.

I second the use of phosphor bronze, my 1902 Toledo engine has phosphor bronze used on the crosshead and some of the bearings.

-CB

[barts]

Sintered bronze works very well indeed, and is forgiving of a momentary loss of lubrication, which the solid bronze alloys are not, often scoring the journal if left to continue. A friend has had very good luck on his powerful steeple compound with bronze bearing shells with a thin layer of tin babbit, machined to fit precisely in both the bedplate (which was line bored for the shells) and the hard-chromed crank. Since it's a steeple, these are not split bearings, although that should not matter if the split halves register properly. The nice part is that since these are machined to fit, he was able to make an extra pair should they ever be needed.

Plastic materials work very well indeed in areas w/ low PV; in valve gear bushings they're ideal, and do much to hold down any noise. I've not tried the really high-tech (e.g. expensive) plastics, though.

Rainbow's compound engine came fitted with roller bearings; I've not had the bottom end apart, but the word is that it's quite difficult to reassemble properly. I think the AVL engine has needle rollers; if I remember correctly the crank is in two parts (each half D-shaped) at the center journal, held together with the inner needle roller race.

Plain bearings have the advantage of being much more tolerant of dirt and salt water; on some headings a cross sea + wind can send salt spray onto Rainbow's engine. Lots of lube before, during and after steaming is needed.

An engine made largely from nickle aluminum bronze would be ideal for salt water.

Rainbow's engine:

EngineStarboard_0858.jpg (138.58 KiB) Viewed 15265 times

- Bart

[steamboatjack]

I use Iglidur bushes on all my engines for these minor bearings, stock sizes (metric) and hard & ground pins make a good job.
Regards
Jack

[barts]

This is an interesting quick read:

https://polyfluoroltd.com/blog/demystifying-iglidur/

- Bart

[Mike Rometer]

Yes, a good one that Bart. I spotted it yesterday, it helped the understanding a great deal.