On Sun, 25 Mar 2012 13:26:37 -0700, Bill Martin wrote:

On 03/24/2012 12:05 PM, Tim Wescott wrote:
On Sat, 24 Mar 2012 10:57:03 -0700, durabol wrote:

I'm new to electroplating and was wondering if anyone could provide
some insight (and save me from reinventing the wheel) in the following
methods of electroplating an aluminium cylinder bore both for
protective reasons and also restoring a worn cylinder bore back to
spec. so don't need oversize pistons. This is for a homemade two-
stroke engine, see http://groups.yahoo.com/group/DIY_2S/ for more
information.

Cylinder Bore Protective Plating:
-Hard Anodizing, high silicon aluminium, easiest -Electroless
Nickel-Phosphorous/NiP: can do it in one step, hardness close to
chrome -Nickel Cobalt: not sure if can get enough cobalt in nickel to
be useful?
-Nickel/Suspended Particles: trapping hard particles suspended in
solution into nickel plating
-Nitride: similar to how some metal tools are protected, not sure if
possible/practical
-Hard Chrome: tested and proven but an involved process

Plating Cylinder Bore Back to Spec., need thick deposit, these are
some metal I thought would be possible: -copper -nickel
-iron
-zinc
-tin: have heard of pistons being plated with tin for less friction

How big of an engine? What's it for? Will you find joy when it
finishes first in a 1000 mile race, or when it manages to run once on a
test stand?


Does anyone still hard anodize cylinder bores? I know there was a
brief rage for it around 2000 or so with model airplane engines, but it
seems that everyone doing it went back to hard chrome or nickel.

Keep in mind that anodizing is not a plating process. The surface does
grow, because given the same amount of aluminum, aluminum oxide is
bigger than just aluminum -- but the anodizing penetrates into the
parent material as much as it grows out of it. The anodizing is way
hard (it's basically sapphire), but if it were such a hot-s**t way of
doing it, why isn't it still done by model airplane engine
manufacturers?

Maybe heat transfer is not so good? Insulators are not usually good heat
conductors. Some exceptions..diamond comes to mind.

It could be. Or maybe it doesn't stand up so well when you abuse the
engine. Or maybe it's because it was pioneered by a Russian company that
ended up having typical Russian QA problems (Norvel, now NV engines --
they got a reputation as being really good engines as long as you
stripped your brand new engine down to the component parts, washed off
all the chips left in the engine, and reassembled).

OS Engines, who is The Name in reliable mid-priced model airplane engines
these days, toyed with it but rapidly went back to nickel plated brass or
aluminum cylinder liners.

(The state of the art seems to be hard-chromed brass or aluminum liner,
and a high-silicon piston. Sometimes the brass or aluminum liner is
nickel plated. A normal engine, when cold, has a slightly too-tight fit
at TDC. As the engine heats, the cylinder liner expands ever so slightly
more than the piston, and the fit becomes perfect. If you adjust the
thing too lean and get a too-hot run, you get low power, excessive blow-
by, and when things cool down an undamaged engine. Most other piston/
liner combinations that have good wear qualities will let the piston
expand more than the cylinder, so at the end of that same really lean run
you'll have a galled piston or liner, or a loose piston/cylinder fit,
neither of which is a Good Thing).

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com