Hello

I think the principle of ABC-engine should be described to give some idea WHY to break engine in at a reasonable hot temperature

A) Aluminum piston
B) Bronze cylinder
C) Chrome plating on a cylinder

Chrome is for strengthening the bronze surface.

Aluminum /Bronze is a clever pair for an engine. Bronze expanses more when heated than aluminum. So when the engine heats, the tolerance grows, the friction reduces. I can imagine an overheat situation the Piston/Cylinder gap even leaks part of the compression and so limits some of the top power which is a good balancing thing when an engine is overheated. Looks like someone has planned this! Maybe the same clever person have planned the cylinder conical. The gap is smallest at the top. So put the piston to its lowest point when cooling!

Aluminum/Bronze kind of balances the engine tolerance. Imagine opposite way working engine (doesn't exist i hope) : when hot, the friction grows and the engine heats more. This situation would also happen when the materials are both the same if the piston heats most and the cylinder is well cooled. So put the piston to its lowest point when cooling! another reason to put the piston to its lowest point when cooling!

Imagine now, you try to 'help' your engine by extra cooling fan over a cylinder: You cool the cylinder head. The cylinder shrinks, pistons expanded, and you ADDED friction.

When cold, a new ABC engine is sometimes terribly tight! At once it is heated, it will have more gap and it turns more easily. Now, when you start first time your engine, you should get it to hot (lease friction) running environment. This should be easy, because you have the new engine and so the maximum friction, which heats your engine ALOT!

So, run it in a short burst to get the normal running environment, but then stop it because you would overheat because of the great friction.

Slowly after some time the piston worns (breaks in) to its best dimensions and shape and this reduces the friction to normal level. At this point you can run the engine constantly. And you are done.

Imagine you break it in cool: you have maximum tightness and friction and your engine is worn too quickly.

So break it in hot, but reasonable! You don't want to melt the piston.

One more thing I want to say: I believe Castor oil conforms a polymer surface like varnish over a piston at a long time sequence. It has brown color and it feels like Teflon plating when you touch it. I think Castor oil tightens the piston gap quite alot.

Sorry if my technical English is limited. I just hope this clears some confusion. If someone wants to correct or disagree with my ideas, please feel free to. If you are 'other school' please try to explain a bit.

Jyrki