Originally Posted by
Olympia463
Here we go again. The myths that surround the Merlins built by Packard still swirl around. Believe me, I worked on Merlins in the 1950s (I was a graduate apprentice in the Rolls-Royce Hillington factory) and one day we decided to see if a supercharger built in America would fit an engine built in the UK. There had been a lot of nonsense talked about Packard 'tightening up the tolerances' etc. We had dozens of Packard 66s out in the yard in the original packing cases (the batch built right at the end of the war and never needed), and brought one into the experimental shop, and removed the supercharger. We brought a supercharger off one of our Merlins and having inserted the locating dowels, we offered it up to the Packard. Perfect fit - it just slid on to the dowels with no problems. We didn't go as far as bolting it on and testing the engine, but I have no doubt it would have worked fine. We overhauled a batch of these 66s and they were fitted to Heinkel 111s which the Spanish Airforce needed when the German engines reached the end of their lives, There was NO material difference between a Hillington engine and a Packard one if you excepted the makers plate. Packard were issued with a complete set of gauges for every part of the Merlin, and I have no doubt they used them.
If you read Stanley Hooker's autobiography it explains that the early Rolls-Royce Merlin engines were built to their own drawing/tolerance standards, but when the Ford factories were engaged to build Merlins they initially said that they couldn't to the RR drawings. RR staff (might have been Hooker himself) are reputed to have said "I suppose you find our tolerances too difficult" to which the Ford response was "on the contrary, your tolerances are far wider than we use in motor cars, if we build to them nothing will fit". As a result Ford redrew all the RR Merlin drawings to ensure proper mass-production tolerances and subsequently these were the drawings used by Packard. The increasing reliability of Merlins as WW2 carried on is probably indicative of these manufacturing improvements as well as the RR method of eliminating weaknesses serially by running at increased power until the next thing broke. The magneto-drive skewgear failures were later traced to the tolerance build-up of the assembly being inadequate.
Packard also provided a lot of information to Britain about the metals to use in the big-end plain bearing shells, at the time this was very secret stuff and even now there is a lot of incorrect information about. I had a long chat with one of the Shuttleworth collection engineers about it, he said that they use parts that are essentially identical to the Packard specification and have no more trouble whereas older engines such as the Kestrel in the Hawker Hind are much more problematic and subject to erosion if the engine runs too hot because the wind down radiator is not wound down far enough and doesn't provide enough cooling.