Darrell Walker writes:
> So, is any of this worth-while? The theory behind the ceramic coating
> (which probably wasn't available them Kas Kastner wrote the comp prep
> manual) seems sound (keeping the combustion heat in the chamber), but then
> most snake oil sounds good when the salesman is talking :-).
My only experience with ceramic-coated pistons was for a bus customer in
the early `90s which had specified such in the Detroit Diesel engines
provided. Ultimately, the coated pistons were an enormous PITA. There may
have been improvements in such in the meantime, but for previous
flame-sprayed coatings, the great danger of them in any engine is chipping
or flaking. The ceramics used are typically very brittle and very, very
hard, and if the coating sheds or flakes, those very abrasive particles do
wind up in the engine.
Beyond that, the incremental improvement in thermal efficiency is actually
quite small.
As for dry lubricants, there, too, unless there have been improvements in
materials and process, I wonder about them. We've used dry-lubricated parts
in the past (these used a baked-on process at something like 400-450 deg.
F), and, if similar, max. piston temps would likely be higher than the
dry-lube application temp, so the coating could degrade. I would also
wonder about how this works in combination with what is already put on the
skirts by most piston manufacturers to avoid scuffing during break-in.
A really good polish of the top of the piston to the ring lands will help
minimize carbon deposition. It's also simple and cheap.
Cheers.
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