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Packard Merlins were built to Rolls-Royce specs and standards.
No, they were not. There were built to more stringent standards.
Parts built by Packard were interchangeable with parts made by Rolls-Royce and Ford UK.
Not all parts in all equivalent engines. R-R still had many hand fit parts and much "File to fit" in their engines.
".... No, they were not. There were built to more stringent standards."
They most surely were built to different standards ..... BSI for the UK builds and American Standard for Packard builds (and De Havilland and AV Roe employment in Canada for Mossies and Lancs).
Packard Merlins were surely built to Rolls-Royce drawings, even if they had to be redrawn for American conventions. So I can't see why Packard Merlins were "built to more stringent standards".
Apart from the eronious term "file to fit", did Rolls-Royce production Merlins (as opposed to those built in the experimental shop) have parts individually fitted? I have my doubts, especially for engines built by Ford UK.
During the life of the Merlin almost 1,000 modifications were issued by Rolls-Royce to increase reliability or simplify manufacture. Packard initiated some of these as well as a number which applied only to Packard-built engines....A few of the more significant changes contributed by Packard were: Introduction of the two-piece cylinder block; introduction of a new design water pump with sealed ball bearings; use of a continuously variable ratio supercharger drive....Although it has been reported in some prior publications that the design of the Packard epicyclic two-speed supercharger drive was one derived from on in use by Wright Aeronautical, that is not the case...(page 7)
Here is an analysis of the Packard Merlin's construction; it should help answer several questions:
View attachment 246126
According to this, Rolls-Royce continually modified the Merlin to make it easier to build on both sides of the Atlantic; Packard helped contribute innovations to the overall design, as well as developing features unique to their version of the Merlin:
Also attached is a description of how R-R analysed early Merlin performance.
Introduction of the two-piece cylinder block
use of a continuously variable ratio supercharger drive
Thanks for those files Aozora.
A couple of things I would take issue with:
...they didn't design or develop the 2 piece cylinder block. Rolls-Royce did, and the only reason RR didn't introduce it earlier was because they were busy building engines for the war effort. RR waited until they started 60-series production before they went to the two piece block.
On 2 August 1940 three representatives from Rolls-Royce came to talk to Vincent about the engine and "almost immediately after their arrival they raised the question as to what type of engine block we were prepared to tool up for. Up to that time we had never heard of the two piece block....They showed us drawings of the two-piece cylinder block and stated that in their opinion we should tool up for this improved two-piece construction....(Actually the two-piece cylinder design was modified by Packard to facilitate manufacture and was used only in engines made by Packard. Rolls-Royce continued to use single-piece construction for some time before they were able to switch...when they finally did it was one designed by themselves and somewhat different from Packard's. For the sake of uniformity Packard switched to the Rolls-Royce design at that point.)
Packard Merlins did not have a continuously variable supercharger drive. They had two distinct ratios.
Did they sound any different or would that be a product of their mountings and exhaust systems?
Thanks for those files Aozora.
That's all good, but they didn't design or develop the 2 piece cylinder block. Rolls-Royce did, and the only reason RR didn't introduce it earlier was because they were busy building engines for the war effort. RR waited until they started 60-series production before they went to the two piece block.
No the 2 piece clock was introduced in the XX series (2 speed, single stage) engines. Later versions of the 45 (Spit 5, single speed, single stage) had it to.
True the XX (and 21) were 1 piece blocks. All the later were 2 piece. That's why I said XX series, should have made myself more clear.