# Bronze vs brass vs cast iron for cylinders and Pistons



## Chris.srch (Sep 16, 2015)

Looking for some feedback as to why bronze cylinders and Pistons with o rings seem so much more popular on scale models compared to Castiron

As far as I can tell cast iron to cast iron has low drag is cheaper and easy to machine. 
What am I missing here

My friend wants me to make him a simple pair of cylinders 1.75 bore 2 inch stroke. 

If cast iron is suitable would it also be safe to use on the D valve as well? 

I have only worked with steel and brass/bronze in the past


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## placitassteam (Jan 2, 2008)

I have only worked in 1/20 scale with brass and bronze and don't know anybody that uses cast iron in that scale. However I would guess that in the size you are talking about that cast iron would be more common. The main problem I see with cast iron is that it can rust.


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## Chris.srch (Sep 16, 2015)

In smaller scale can you think of any real reasons why bronze seems more popular other then rust? 


Do you know if o rings can still be used?

I am tryin to save him some money since this isn't a detailed project... He wants to toss these on the back of his bike... 
Basically I'm just going to scale up the pensy a3 switcher plans


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## Totalwrecker (Feb 26, 2009)

A steam bike? 
Or are you thinking infernal combustion with a spark plug?
I think Cast Iron is too porous, they use steel liners in car motors.
John


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## Chris.srch (Sep 16, 2015)

Yes a steam bike. Using a watertube boiler. 

And I like this because it gives me an opportunity to try some cost-cutting ideas so I might be able to use on my G gauge live steamers Since brass and bronze A rather pricey around me


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## Totalwrecker (Feb 26, 2009)

you have company....


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## BigRedOne (Dec 13, 2012)

In a commercially viable model, design has to account for the cost of materials, but also the cost of labor and tooling. The material also has to have properties which work for the size of the part (for instance, can it take tapped threads in 2mm, if that's needed for the scale?)

I've seen cast iron cylinders in 5 inch gauge models at the size you propose, so (as far as I'm aware) it's a fine choice for cylinder castings. I didn't see the pistons, so don't know what they were made out of.


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## xo18thfa (Jan 2, 2008)

In the Gauge 1 hobby, brass cylinders with O-rings are the norm. We run at lower pressures then the ride-on guys. maybe 60 or 70 PSI max, but usually around 40. Use a free machining type of brass (like 360). Bore the cylinder to a few thou under, ream and then a very light lap. That's all. the ring is the least friction fit possible and still maintain a seal. D-valves on brass cylinders should be bronze.

Sounds like you are going to operate at higher pressures. Cast iron is a better choice. It is more durable, it will last longer. Pretty easy to machine. Cast iron rings are widely used. Although bronze rings should work too. Bronze D-valve will work just fine. Use a reliable mechanical lubricator with steam oil. If the lubricator craps out and portface on a cast iron D-Valve dries out, you will have big problems (how do I know that).

Many years ago, Bob Maynard did a ride-on steam loco series (the Clishay) where he used cold roll steel for cylinders. That was a popular engine and the CRS cylinders worked well.

As far as rusting cast iron a good shut down procedure prevents that. Shut off the boiler fire, let the pressure cool/drop to 40 PSI, open the blow downs and let it drain. Connect an air compressor line to the down down and briefly run the engine on air. It will dry out and the lubricator will pump in some oil. Sometime the top cover has a screw in it, so you can squirt in some oil for storage.

1.750 x 2.000 on a bike. That will be so cool.


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## lotsasteam (Jan 3, 2008)

*Thats what youre building?*

http://motherboard.vice.com/de/read...mpfmaschine-angetrieben-243?utm_source=vicefb


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## seadawg (Jan 2, 2008)

Yep, I *NEED *one!!


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