Material for pistons?

[MiLyNielsen]

Hello HMEM, i am a 1st year machinist, who have recently bought the plans for the V12-factory V8 (I know it is gonna be hard one to make, but i have many years to finish it ) And am starting to make the pistons (Have turned 2 blanks down to OD on the same rod), but then my 'supervisor' (I work at a university, and sometimes there is not enough work, so i either have to come up with my own projects, or sit in the front of a computer doing nothing), came and said that i shouldn't be using aluminium for the pistons.
But after having browsed this website and others, i was pretty sure that aluminium was the best choice for the pistons.

So my questions in short is; Is aluminium the best choice for the pistons?
I tried a quick google and on here the most common material was 7075 aluminium T6

(Sorry if my english is hard to understand, it's not my native language)

Kindly
MiLyNielsen

 

[lohring]

It depends on many factors. High performance small engines use a combination of high silicon aluminum alloy pistons with plated aluminum or brass cylinder liners. Some also use chrome plated steel liners. Nikasil plating on aluminum is the preferred method for aluminum, though chrome plating is used as well. The idea is to match the thermal expansion of the piston and liner. High silicon aluminum has a comparatively low expansion and plating gives a smooth, long wearing liner surface. It is also important to have a light piston that dissipates heat well. All have been used with ringed as well as ringless piston and sleeve combinations.

In the past many engines used cast iron pistons with steel liners. That combination works well with a ringless piston that is a lapped fit in the liner. You need a lot of castor oil in the fuel for lubrication and sealing. I believe that that system is easier to work with. Read through the 1/4 scale Merlin thread for details on building a complicated V 12 engine.

Lohring Miller

 

[stevehuckss396]

7075 is great for pistons. my typical combination is . .

12L14 steel cylinder
7075 aluminum piston
Gray cast iron rings

I have models with this combination that have been running for almost 8 years without a problem. I do put a small amount of wd40 in my fuel.

 

[Brian Rupnow]

For slower running engines, one of the best combinations is grey cast iron for both piston and cylinders because of it's high graphite content. It is self lubricating to a large extent because of this high graphite content. For fast running engines, aluminum is great as a piston because it is much lighter, so there is less inertia to overcome. The caveat with aluminum pistons is that they pretty well must be ran with cast iron or viton rings, and have some clearance in the cylinder. Aluminum has a higher expansion factor than steel, so if you try to run aluminum pistons with a lapped fit (0 clearance) in the cylinder, they will expand and seize in the bore..