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Model Engineering Glossary: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Pistons and Liners

There are many different materials that you can use for pistons and liners, some work better than others.

Cast IronSteelThis is the easiest to machine and get a running engine.
Cast IronCast IronFavoured by ET Westbury. Works well as expansion rates match
AluminiumCast IronThis is quite common, especially with cast iron rings. The piston mass is low which reduces vibration.
SteelSteelA good combination to make
SteelPhosphor BronzeHave used this in a small steam engine
AluminiumSteelCommon with cast iron rings
Phosphor BronzeCast IronQuite a few steam engines with PB pistons with cast iron rings

Aluminium Piston and Cast Iron Cylinder

This shows the cylinder and piston from my wood and metal beam engine.

As you can see from this obscure view of the piston I did not use piston rings and even so the engine has kept compression.

With steam engines it is quite common to lag the cylinder to insulate it.

Aluminium pistons reduce the reciprocating mass and so reduce vibration (this particular example is rather poor as I offset that advantage by making a brass connecting rod).

Steel Piston and Phosphor Bronze Cylinder

This combination took quite a lot of time to hone, but this was partly due to the fact that the cylinder and head are one piece.

After a few hours of running time this now runs as sweet as sweet

I must note that I have only ever run this on compressed air and not on steam and so not sure how well this combination will work at higher temperatures.

Aluminium Piston and Steel Cylinder

This is quite a common combination.

This shows the cylinders and liners from my 5 cylinder rotary engine.

The piston and master conrod are shown on the far left.

In this particular case the pistons are plain with no rings.

You need to take care honing the cylinders and you must wash them to remove any grinding paste before fitting the piston. After I got a good fit I then ran the engine with lots of oil to bed the pistons in.

Phosphor Bronze Piston and Cast Iron Cylinder

This is quite a favourite of Stuart Models and many others.

The piston is quite shallow in most double acting steam engines - this is due to the fact that the piston does not need to react any side loads as the conrod is supported in a bearing in the cylinder end cap.

This piston has two cast iron rings in the one groove.

This particular cylinder and pistone combination belong to a Stuart Beam engine.

See also: Aluminium, Cast Iron, Pistons.

Model Engineering Glossary: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z