Looking to rebuild a few engines and would get the piston or cylinder chromed. Some manufactures chrome the sleeves others (K&B for one) chromed the piston (usually the top half of the piston). Question, any option on which is better for performance?

GMA use to chrome sleeves and would use a rather course hone to hold oil, Super Tiger did chrome sleeves in some models of their ringed engines, K&B in their speed engines (Series 61 & 64) chromed that top half of the piston. Both approaches produced top competitive engines. Seems the piston is easier to do does anyone have experience with doing either?

Best, DennisT

Lauri,
I understand your point for aluminum pistons but if they can chrome the aluminum sleeves (AAC) why not do the piston instead?

Lauri told you, but you didn't pick it up.  In an AAC engine, the piston and cylinder are made out of different alloys of aluminum.

The piston is a hypereutectic silicon-aluminum alloy -- "hypereutectic" means that there's more silicon in the mix than will stay dissolved when the metal solidifies out of the melt.  I'm not sure of the details, but the result is a solid that's a mix of solid aluminum with as much silicon as will stay dissolved, and little grains of whatever the other stuff is (?).

The cylinder is made of a more ordinary aluminum alloy.

This, by the way, is the secret sauce to AAC and ABC engines -- hypereutectic silicon-aluminum alloy has a lower coefficient of thermal expansion than either brass or boring old aluminum -- so when the engine gets hot, the fit stays the same or even gets looser.  So an AAC or ABC engine will survive overheating better than iron/steel combinations.  And chrome and hypereutectic silicon-aluminum are both resistant to wear, so the engine lasts forever, the engine market collapses, and we all end up flying electric.

That's what Lauri didn't tell you.

What he did tell you is that the stuff the piston's made out of is hard to chrome, and has a better coefficient of friction against chrome than the stuff the cylinder's made out of.  So it's better to leave it un-chromed.

The stuff the cylinder liner is made out of is easier to chrome, and has a worse coefficient of friction against chrome than the stuff the piston's made out of.  So it's better to chrome it.

I think Lauri pointed the way for you.  Cast iron and steel are very different materials, both in coefficient of friction and in how easy they're going to be to plate.  I would do some internet digging for the answers to how easy they are to plate and how low the friction will be, and go from there.

You're not mentioning piston materials for your old-time examples, and I'm not enough in the know to, well -- know.

I'm guessing that steel is easier to plate in general than cast iron -- or at least most steel alloys.  Cast iron is also a hyperutectic alloy, only carbon-iron.  This makes it inherently granular I know from reading about it -- and working with the stuff just bears this out -- cast iron normally has little flakes of graphite, possible little crystals of iron carbide, all in a relatively soft steel matrix. But there's all sorts of other alloying materials, process variations, and heat treatments to confuse things, so saying something is "cast iron" puts it into a pretty broad class -- but every kind of cast iron involves an intimate mix of steel and other stuff, and you'd want the chrome to stick to all of that.

I also have personal experience with my dad's shop selling cast hinges for antique cars (both cast iron and cast bronze).  It was pretty much luck of the draw on whether a part would come out of the casting shop looking good, or with little pinholes all over it.  This probably doesn't apply to what you're doing, because in that case it was due to variations in the process at the small casting company that we employed, leading to surface porosity in the otherwise perfectly good castings that they sold us.

On the other hand I know that it's harder to electroplate the inside of a cylinder, because you need to get an electrode inside the length of the cylinder, and you probably need to circulate your electroplate solution -- where those two difficulties balance, I don't know.

Will you be chrome-plating these yourself, or will you be going to a shop?  If the latter, I'd say you should go to the shop with a piston and a sleeve in hand, and ask.  If they'll deal with you at all, they'll tell you which one they'd rather work with, and if it's a shop that does hard chrome for industrial uses (which is what you're looking for) they'll probably also know what has the lowest coefficient of friction, to boot.  If the former -- you have a long road ahead of you, and keep in mind that hexavalent chromium really is toxic, and any chromium is a boogeyman in the eyes of the (somewhat) environmentally conscious public.  To me it'd be worth it to take stuff to a shop, just so the shop can bear the burden of filling out all the paperwork.