Aviation History

The Story of when Ford UK Refused to Build Rolls Royce Merlin Engines because the Tolerances Rolls Royce allowed were Looser than Ford was Willing to Work With

Ford re-drew the blue-prints for the Merlin, making it more suitable for mass production, and by 1944, over 400 engines a week were flowing out of the plants.

The Rolls Royce Merlin is a direct descendant of the Kestrel engine, the power unit from the Hawker Hart and its many variants; an enlarged version of which powered the Supermarine S6 which won the Schneider Trophy for Britain in 1929. This led directly to the Spitfire aircraft powered by the new engine now called the Merlin.

According to ShortFinals.org, in 1941, in Trafford Park, Manchester, Ford UK had two assembly plants where they were told to build Rolls-Royce Merlins – lots of them! At the time, this engine was in the vast majority of British fighters and bombers, including the two which had just won the Battle of Britain, the Supermarine Spitfire and the Hawker Hurricane.

In his book Not Much Of An Engineer, Rolls Royce supercharger designer Stanley Hooker states that Ford UK looked at the Merlin engine drawings and said “we can’t build an engine to those tolerances.” Hooker said loftily (his words) “I suppose the tolerances are too tight for you?” ” No, they are much too loose – we use much tighter tolerances for car engines so all the parts are truly interchangeable without any hand adjustment needed.”

Ford re-drew the blue-prints for the Merlin, making it more suitable for mass production, and by 1944, over 400 engines a week were flowing out of the plants.

This print is available in multiple sizes from AircraftProfilePrints.com – CLICK HERE TO GET YOURS. Supermarine Spitfire Mk Vb – W3257 E-FY – 1941

“And they were very good engines too” said Hooker.

The final total came to 30,428. This was only 2,000 less than the main Rolls-Royce plant at Nightingale Road, Derby (although there were several other plants producing Merlins in the UK).

The first Merlin engine developed 880hp but by the time the last mark of Merlin was produced the power output was 2030hp.

The Merlin engine was then enlarged still further and named the Griffon. Aircraft which were powered by the Merlin engine include the Lancaster, Spitfire, Halifax, Hurricane, Battle, Defiant, Whitley, Mosquito, Hornet, York, Lincoln and North American Mustang.

Hooker’s book is an excellent read about the development of the Merlin engine and then the early jet engines. Hooker eventually saved Rolls Royce after it went broke developing the RB211 three-shaft jet engine, which became today’s very powerful and very fuel-efficient Trent engine.

Photo credit: Crown Copyright

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Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

View Comments

  • The Griffon engine was NOT a direct evolution of the Merlin. To start with the Griffon rotated in the opposite direction to the Merlin. While the Merlin might have been derived from the Kestrel, the Griffon engine was actually a development of the engine that powered the Supermarine S6B.

  • Ford/Briggs later made combustion chamber assemblies for early jet engines. The original collector ring design was a welded assembly of several parts, Ford made a tool to make it in one piece!

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