On Tuesday 18th 2004f May 2004, Philippe Cabon wrote:

I am very new at diesel engines,interrested particularly in the smallest.I have been gathering information (internet)on them in the past months.
This is the first site which is quite complete and on (the,a) subject.At least on a specimen!Impressive one!BRAVO!
Here is my questions:
I know american and english(europeans) engines differ on the metal combination between cylinder and piston:
-steel/steel on americans.
-steel/cast iron on europeans.
What are the advantages/disadvantages?
Which last longer?.
What differences in running in?
I learned much when practising vintage scale replicas 0.32c and 0.36cc.These are having a cast iron piston.I discovered something strange:
When started (a little bit rich on the prime),you have to increase compression on little diesels, whereas many say to reduce it(when speaking diesels generally).Why?

Philippe,

Neither soft steel cylinders nor pistons are ideal for diesels.

Hardened steel is a good cylinder choice.

Both cast-iron and hardened steel pistons have merit.
When hot, a cast-iron piston will expand less than the steel cylinder. This can give good seal when cold and low friction when hot. It can be, and generally is, fitted tightly when new so as to "wear" in to fit.

A hardened steel piston (at a different hardness from the cylinder) is fitted close to ideal clearance when new. It will be free when both cold and hot, will always have an oil film and will thus have a longer life. It is much more exacting to make. In a cooler running diesel, it will have good seal both cold and hot, start readily both cold and hot, have low friction both cold and hot and run well at both low and high RPM.

When starting, I prefer to back the compression off slightly. The engine will start at lower RPM and it is being cautious. A small engine can be damaged when overcompressed or flooded.
Advancing the compression when starting could allow for you to partially compensate for a looser piston fit or a slower flick of the propeller.

Peter