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Piston Rings


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Graham Porcas23/08/2019 16:06:00
6 forum posts

I need to make some new rings for my 1500 Speedy, when I took it to bits there was virtually nothing left, just a few slivers of string!!

Coming from G1 I have used PTFE rings backed with Viton O rings which work very well, in my opinion much better than the long recommended graphite yarn.

I have a nice piece of filled PEEK which I was thinking of experimenting with, anyone have any experience with this compared with graphite filled PTFE?

For 5" I intend to make one piece rings as proposed by Artisan, any comments about how these compare with my G1 experience?

The PEEK clearly has some carbon loading, it's black, but whether this is enough to give good abrasion resistance I'm not sure, the cylinders are bronze so I'm concerned about wear.

The part was left over from an F1 application where wear was unimportant, as long as they made it to the finishing line!

The alternative would be to get hold of some 25% or 35% graphite filled PTFE but it looks like I have to buy a meter or two when I really only want 150mm max, and it's expensive.

The fallback option is braided graphite square yarn which a lot of friends still swear by.


Neil Wyatt23/08/2019 17:29:16
17088 forum posts
690 photos
76 articles

PEEK is very tough, but i don't think it is as slippy and therefore as wear resistant as PTFE.

In the past I have bought PTFE rod in 100mm lengths, can't remember where from.


Roger Woollett23/08/2019 18:16:43
110 forum posts
4 photos

Possibly from Direct Plastics

Direct Plastics

Not used them for a while but happy when I did.

Andrew Johnston23/08/2019 18:42:19
5115 forum posts
594 photos

PEEK is a high temperature plastic with excellent wear characteristics. Virgin PEEK machines very well, like delrin. If it's black then it probably contains carbon fibre, PTFE and graphite which improve the tribological properties. I've not machined carbon filled PTFE, but virgin PTFE is horrible stuff, creepier than Uruah Heep. Glass filled PTFE machines very nicely and is stable, but the glass fibres probably aren't a good idea in this application.

I'd go for the black PEEK. If you think PTFE is expensive sit down before you ask how much to buy PEEK.


julian atkins23/08/2019 22:24:53
1224 forum posts
353 photos

Hello Graham,

Bit of a can of worms here.

Assume "Pistons" as per your thread title, which previously had graphite asbestos packing instead of far superior square braided graphite asbestos packing.

You can still get square braided graphite asbestos packing on ebay - it crops up from time to time, and if properly selected and fitted ought to last 10 years hard use on regular passenger hauling. There is a bit of an art how to fit this type of packing.

I would recommend you investigate this route rather than having to make new pistons and rods etc and all the fuss required with PTFE, and consequent greater expense and time involved.

PEEK is an unknown quantity so far as piston rings are concerned on a miniature locomotive, and in any event how are you going to get them going onto the LBSC piston dimensions?

Of far more concern would be the piston valves and their bores on an old 'Speedy', if the piston packing in the cylinder bores is already 'shot'.



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