Piston material for gunmetal cylinder

[StewAParticipant @stewa]

I’ve bought some castings from a well known auction site to build a Stuart S50. The cylinder is gunmetal and I’m not sure what material to use for the piston and slide valve. I have the plans for an S50 but they show a cast iron cylinder so the parts list isn’t much help. Has anyone built an S50 with gunmetal cylinder that can shed some light.

[JasonBModerator @jasonb]

Are you going to run on steal or air?

Aluminium would be my choice particularly if just air running for less reciprocating weight. If going for steam then a piece of cast iron bar or brass would be OK

[StewAParticipant @stewa]

Intention is to run on steam. Would you run cast iron for both piston and slide valve?

[Thor 🇳🇴Participant @thor]

I have used stainless steel (303) for pistons and slide valves when running on steam (gunmetal cylinders).

Thor

[JasonBModerator @jasonb]

I would most likely opt for brass for the slide valve

[StewAParticipant @stewa]

<p style=”text-align: left;”>@thor do you know what grade of stainless steel you used? My experience of using stainless nuts and bolts is they tend to gall and seize up.</p>

[JasonBModerator @jasonb]

There is a clue in his post – 303

Unlike a nut and bolt you won’t be running stainless on stainless so should not gall. Many a stainless steel piston or valve rod running through GM glands without problem.303 is easy to machine.

[StewAParticipant @stewa]

JasonB

Is it OK to run 2 soft metals together?

[StewAParticipant @stewa]

JasonB sorry I didn’t spot the 303 in the post.

[BazyleParticipant @bazyle]

Brass is ‘nearer’ to gunmetal to reduce electrolytic corrosion.

[JasonBModerator @jasonb]

Brass and GM/Bronze are quite commonly run together. Many a stationary engine model with GM cylinders will have brass piston and valve specified. A lot of Anthony Mounts designs do as well as some of Reeves. Engines like the Stuart Progress osscilator runs GM cylinder against a GM valve face.

[Clive Brown 1Participant @clivebrown1]

I suspect material choice is not at all critical, especially for such a small bore, but I’d go for brass. Easily obtained, easy to machine, corrosion-free, good bearing properties, similar expansion to cylinder material. What’s not to like?

[StewAParticipant @stewa]

<p style=”text-align: left;”>Consensus of opinion seems to be brass so that’s what I’ll go with. Thanks everyone for your help.</p>

[StewAParticipant @stewa]

Does anyone know why I’m getting all the extra characters at the beginning and end of some of my posts?

[duncan webster 1Participant @duncanwebster1]

I would not use cast iron in a bronze cylinder. If you ever run on steam you then have to go through the rigmarole of getting the condensate out or run the risk of it rusting up.

[Tim StevensParticipant @timstevens64731]

A response about the ‘extra characters’ that StewA is suffering:

All computer text starts with instructions about the typeface, the size, the spacing, and so on. Then comes the binary code for the letters, punctuation etc. The computer turns this long string of ones & zeros into what you see on the screen, and should not show any of the coding messages. Here, there is a fault in any of:

a) the program in which the text was originally keyed-in;

b) the program in which it was sent to ME-HQ;

c) the program which turned that text into what we now see on our screens.

d) and perhaps at least some of our own system which allows the electronic message via wire or fibre to appear on our screens. But this is doubtful, as it seems others get the same effect or at least something similar.

And I doubt whether you or I will have ready access to all of these potential sources.

 

Sorry – I did not design any of these systems – Tim

 

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