# Piston and Cylinder materials?



## Greebe (Jan 30, 2010)

I haven't built any steam engines but am planning on putting together one of the Launch style steam engines like in my post here:http://www.homemodelenginemachinist.com/index.php?topic=8083.0

One of the questions I have is about the piston and cylinder materials. Can they both be brass or should they be of different materials? I.e., should the cylinder be brass and the piston aluminum or mild steel?

I didn't know if there would be galling of the cylinder and piston if they are both made of brass.

Thanks
Greebe


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## Metal Butcher (Jan 30, 2010)

Its a good idea to use dissimilar metal for piston and cylinder combination's.

Brass on brass is a bad choice. It will gall for sure.

With a brass cylinder I would use. From the top, starting with the best choice.

1) cast iron.
2) 12L14 steel, or other steel
3) delrin (acetal)
4) 6061 aluminum

-MB


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## Maryak (Jan 30, 2010)

Greebe,

There's a great thread running on this subject. Have a look at:

http://www.homemodelenginemachinist.com/index.php?topic=8088.msg85452#msg85452

Best Regards
Bob


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## ironman (Jan 30, 2010)

The plans call for Cylinder=Aluminum, Piston=Steel, Cylinder Head=Aluminum, Valve and Valve Bearing Blocks=Steel. On my second one, I changed the piston to brass in aluminum cylinder. Doesn't wear the cylinder as much as the steel piston. ironman


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## Blogwitch (Jan 30, 2010)

The best thing to do in a situation like this is to find your matching material pair, then make the most complicated one out of the harder material.

It is much easier to make a new piston rather than a cylinder. So make the cylinder out of the least wear material.


Blogs


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## GWRdriver (Jan 30, 2010)

Blogwitch  said:
			
		

> The best thing to do in a situation like this is to find your matching material pair


That sums it up nicely.


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## Greebe (Jan 31, 2010)

Cool. Perhaps I will go with an aluminum cylinder and a brass piston. The aluminum is cheaper anyhow.

Thanks
Greebe


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## Kaleb (Jan 31, 2010)

I have thought of using a copper cylinder with an aluminium piston, how well will that work?


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## Deanofid (Jan 31, 2010)

Metal Butcher  said:
			
		

> Brass on brass is a bad choice. It will gall for sure.
> -MB



Sorry to disagree with this bit, but brass in brass works very well in a piston/cylinder relationship for steam/air engines.  I have a few engines built this way, and they do not show any signs of galling. I also have a number of plan sets by well known model engineers that use a brass piston in a brass cylinder.

On things that spin, like when using a close fitting brass axle or shaft rotating in a brass sleeve, then you may have a galling problem.

Aluminum will run very well in a brass or CI cylinder, as well. I would avoid steel for a piston in a steam engine simply because it will rust. If the engine will only run on air, you probably won't have that problem.

I agree, appropriate dis-similar metals usually work well. Take expansion factors into consideration if the engine will run hot. 

Dean


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## Jadecy (Jan 31, 2010)

I'm not sure copper is a good choice. I've used the following:

steel in cast iron cylinder (steam and internal combustion)
cast iron in brass cylinder (flame eater and stirling)
aluminum in cast iron cylinder (internal combustion)
brass in brass cylinder (small steam)

I'm sure there are others but this is what I have used.


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## GWRdriver (Feb 3, 2010)

Deanofid  said:
			
		

> I also have a number of plan sets by well known model engineers that use a brass piston in a brass cylinder.


In the cases which come immediately to my mind, IMHO they haven't done it that way because it's the best combination of metals, . . . they've done it because it's the easiest, least expensive, and most convenient path for builders and suppliers and therefore encourages more builders and suppliers to participate. That's not a bad thing of course and hopefully leads those builders to learn more about metals and better bearing combinations.


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## Artie (Feb 3, 2010)

Metal Butcher  said:
			
		

> Brass on brass is a bad choice. It will gall for sure.
> 
> -MB



A further question in the same vein then, the actual slide valve and steam chest. Ive already decided to make my piston from Aluminium as I have brass cylinders.... but...... the slide valve itself. Using the same logic, should it not also be of a dissimilar metal for the same reasons?

Cheers

Rob


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## mklotz (Feb 3, 2010)

> Brass on brass is a bad choice. It will gall for sure.



I'm with Dean on this one. I too have brass on brass engines that have never exhibited any galling. Like Dean, I would avoid brass on brass rotating joints and go for dissimilar metals where convenient.

There must be thousands of model steam engines out there (including most of Elmer Verburg's designs) that use a brass D-valve against a brass valve plate or brass cylinder. Anecdotes aren't evidence, but I've never heard of one exhibiting galling.


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## kcmillin (Feb 4, 2010)

Whay hasn't anybody mentioned bronze? There are many different types. Is bronze a bad idea? Ive heard of leather being used for piston rings in air compressors, why not a steam engine? Or how about a hard wood??? Or a soft wood?? Just throwing out ideas now. Ime not really an expert or anything, Ive always just used whatever I have in the shop. 

kel


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