"Roger (K8RI)" wrote in
:

On Fri, 19 Oct 2007 11:05:32 +0000 (UTC), Bertie the Bunyip
wrote:

Matt Whiting wrote in
:

J.Kahn wrote:

It's not a problem when heating because the head expands faster
than the steel parts so the stress effects are reversed. This is
why the manufacturers have no problem with going from idle to full
power as soon as the engine will take it without stumbling. There
is no such thing as shock heating...

What about the aluminum piston in the steel cylinder?


That can happen too! But the clearances are cgrater ther than it would
be in a valve stem or head to cylinder seat.

If we had that kind of piston to cylinder clearance in an automotive
engine we'd think it was worn out. :-)) At least in the "old days".



Yes, some air cooled engines have tapered bores (when cold) to allow for
different rates of expansion in cylinder base-to-head so that it's
perfectly cylindrical when up to temp, but i don't know of any aircraft
engines that have that feature.



Bertie