Well, the Merlin had a bad habit of its conrods failing (typical 'skimpy' R/R design) & took over a decade for crank end oil-feed,
something Napier (along with oil-jet to piston underside) had in their Lion, from 1918. (R/R Merlin racers tend to trust Allison conrods.
I do have a question you may be able to answer Calum; Do you know why, since Butch Harris was running a 'Merlins to Germany export
programme' for years (at the rate of hundreds a night, sometimes) why didn't the Germans re-use the valve & piston alloys from them,
to solve their own problems in that area?
They ran out of Nickel and after operation torch more or less ran out of Cobalt too.
Without those you cant make Merlin valves or Brightray/Stellite coatings even if you know what they`re made of. I would think
the Germans already knew perfectly well what to use, they just couldnt.
They got just about all their pistons from Mahle, who exclusively favoured very high silicon (i.e. low expansion) pistons over
our high copper alloys. This is a matter of some slightly subjective conjecture about what is best, I have discussed this
with two very senior F1 & ex: F1 piston metallurgists. There are pro`s and cons to both, and it is not definitively clear
which is best at high temperatures. It may be that the available test data does not show up the "slight" edge
the high copper alloys probably have at high temperature as they are not fatigue tests, the former head of
Cosworth tells me that the high copper alloy has the advantage over high silicon in terms of its properties
at high temperature under actual reversing load fatigue (which you wont see on a static test).
On the other hand the inverted V12`s probably had to use high silicon alloys beause you can of course
run a much lower piston to bore clearance when cold compared to high copper, which would have
been highly advantageous with the potential oil into chamber issues (oil in the chamber significantly
lowers the knock limit, right before you`re about to apply full boost for take off).
British reports tend to be derisive of the German high silicon alloys, but we almost exclusively used
high copper alloys, so it is fairly typical for that kind of attitude to develop.
In my opinion, the high copper probably has a very slight edge in high temperature mechanical strength
over the German silicon but it is not a large difference.
There are some erronious British reports which some people have picked up on where they noticed
that the DB 605 had suddenly put in pistons with thicker crowns, this was interpreted as "piston weaknes",
in fact this was done as a somewhat feeble attempt to prolong the life of the pistons when the Germans
were having their "detonation catastrphe" between 1941 and late 1942 due to the use of low Nickel
exhaust valves. The pistons were however not weak, the idea was to conduct a bit more heat out of the
piston through the skirts and thus alleviate a bit of the detonation by helping keep the piston crown a
little bit cooler.
This was eventually just about solved (to a degree, but always capped the allowable boost) by
very elaborate chrome plating of the valves instead of Stellite/Brightray coating and high nickel
base alloy for the valve itself.
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