I have checked out enginehistory.com and other sites - and none of them answers my questions directly. My original question centered around the use of O-rings in the Merlin engine(s).
After a lot of senseless work, I have developed a theory. Mind you, this is only my own guess - there is no guarantee that it is correct. But it makes a rough sort of sense to me, poor fool.
First, I need to refine the basic issue: it appears that the Merlin engines could withstand the extreme temperatures and pressures of incredibly high supercharger boost, while the Allisons could not. IF - this is true, then why should it be so?
What I have divined - after a long and winding road - is that the Merlin's advantage came about as the happy accident of an unfortunate decision. It was not due to any genius or foresight on the part of Rolls-Royce management or engineering. It was simply dumb luck.
To put this in perspective, we might consider the common ancestor of the the RR-Merlin and the Allison V-1710 to to be the Curtiss D-12. This engine was developed in the 1920's and powered the winners of the 1923 and 1925 Schneider Trophy races.
When Allison developed their V-12 engine around 1931, they used the Curtiss D-12 as "inspiration " for their design. The Allison appeared to be basically a Curtiss D-12, scaled up, with a supercharger added. Like the Curtiss, it had Dry Cylinder Liners.
The immediate ancestor of the RR Merlin engine was the RR Kestrel engine. Rolls Royce also used the Curtiss D-12 engine as "inspiration" for their Kestrel design. They made 3 critical differences from the D-12 design, however. One of these was the use of Wet Cylinder Liners, instead of the Curtiss's original Dry Cyliner Liners.
Herein lies the difference: Dry Cylinder Liners are reinforced and supported by the cylinder block metal - Wet Cylinder Liners are not. Therefore, in general, Wet Liners must be made stronger and more robust than Dry Liners.
The Dry Liners of the Allison engine could therefore be made of *relatively* slight and willowy metal shells. The Wet Liners of the RR Kestrel engine were forced to be more massive.
Understand that in the 1920's and 1930's that nobody, absolutely nobody, could anticipate the extreme demands of supercharger boost that were available in the 1940's. It was simply terra incognita.
Therefore, just by the accident of using thicker, stronger Wet Liners, the Rolls-Royce engines had more resilient cylinder liners that were able to stand up to the rigors of super-duper supercharging.
The later generation of Merlin engines, beginning with Merlin Mark 61, used dry liners. I suspect that RR just carried over the design of the earlier Merlin Mark II's wet cylinder liners. The use of O-rings may have had little if anything to do with the robustness of the Merlin engines. It was just the strength and robustness of the cylinder liners.
Some people have commented that the development of the Merlin engine(s) was a triumph of development over design. That is to say that Rolls-Royce management had their heads up their butts. My theory supports this case. If it were not for the "happy" concatenation of more-or-less random events and mistakes, the Merlin engine might never have been fully developed, the Battle of Britain may have been lost, and European history may have been very, very different.
For the want of a nail, a horseshoe was lost. For the want of a horseshoe, a horse was lost. For the want of a horse, a knight was lost. For the want of a knight, a battle was lost. For the want of a battle, a kingdom was lost. Eh?
The Postscript is that the performance of the Allison engine might have been vastly improved by the use of more robust cylinder liners. Alas, by the time this issue became pertinent, the piston engine was on its way out in favor of the jet.
