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Crankcase Material DTD 424


Well Known and Active Forum Website User
Non-VOC Member
The post WW2 Vincent crankcases were castings of aluminium alloy DTD 424.

For aerospace material specifications DTD and D.T.D. represent 'Director(ate) of Technical Development'.

As a clarification, Document Type Definition (DTD) is also an abbreviation in software development/ markup languages

D.T.D. 424 is a material specification issued by the Air Ministry in 1940.
Reading the specification makes it clear that although some scrap may be used it has to be identified and approved by the inspector.
The exact wording can be seen in the Files Section / Materials of:


From time to time one reads slightly derogatory comments about the light alloy used for Vincent crankcases DTD424.
Suggestions that any old rubbish would do are mistaken.

I guess that those making these comments have been influenced by one of Phil Irving's throw away remarks on the lines of 'melted down saucepans'.
While PEI was noted for a dry sense of humour, that sort of casual remark should not be taken too seriously.
PEI Autobiography page 339, writing of the post WW2 era, refers to "a new alloy DTD424, which was a sort of metallic fruit salad made by melting all sorts of the available alloy scrap".
Well, it may have been new to PEI but not to others - DTD424 was issued in Jan1940.
In fact, The Directorate for Technical Development [DTD] was responsible for many of the specifications of materials used in military aircraft during WW2 and was certainly not going to lend its name to any old rubbish.
DTD424 was used in some Spitfire parts and also in some post WW2 car engines such as Jaguar.

Having survived the War, 'P7' was then sold for scrap to Messrs. John Dale Ltd in 1948 for the princely sum of £25; fortunately the historical significance of the aircraft was recognised and she was generously presented to the RAF museum at Colerne. Restored to flying condition in 1968 for the epic film 'The Battle of Britain', she was presented to the BBMF after filming was completed.

"For the Mkll Zephyr and Zodiac 6's, the head made and marketed by Rubery Owen and Co., LTD of Bourne, (designed and developed by the technical associates of Raymond Mays) was made of an aluminium alloy known as DTD 424, the same material as used by Jaguar as used on the XK series."


[http://keithclements.co.uk/jowettnet/dt/tech/jti/jav.pdf - SITE WITHDRAWN]
The following labour times are those recommended by Jowett Cars Ltd, for ..... The crankcase was of aluminium alloy to D.T.D. 424 specification, and wet liners ...
Post WW2 Jowett Javelin:
"The crankcase was of aluminium alloy to D.T.D. 424 specification, and wet liners sat on a joint
washer at the base and were clamped down by the detachable cylinder heads. "

10th July, 1940, when Lord Beaverbrook, the charismatic Minister for Aircraft Production, called on the good folk of the U.K. to help build more urgently needed Spitfires.
This was a PR campaign to get housewives to give up their aluminium saucepans.
Quite irrelevant to aircraft production. Britain could get plenty of aluminium from Canada - it was just short of money to pay for it.

Materials for the construction of aircraft was another of Beaverbrooks concerns. He thought up the idea of getting public participation, not only for the purpose of gathering as much alluminium as possible, but if we (the government) could involve the general public that by donating all the old alluminium saucepans, pots and pans and any other utensil that was made of alluminium, it would impress upon the people that they were 'doing their bit' and should if nothing else, boost public morale. So, the slogan "Saucepans to Spitfires" programme was started and it was a public relations programme that became an inspiration to all.

I hope that some of the above may encourage people to recognise that the Vincent crankcases were not made of any old scrap.

david bowen

Well Known and Active Forum Website User
Non-VOC Member
It must have been PEI sense of Humour! because the joke at the vincent factory was that he spent more time in John Dales drawing office than at vincents !948 /1949 but then came out the much improved Vincent embossed crankcases John Dales plant was 24kms from Stevenage, the home of the De Havilland Mosquito Museum


Well Known and Active Forum Website User
VOC Member
Melted down saucepans would have been a good start for the alloy mix, being that they were as good as pure aluminium. That`s the grade used for deep drawing and forming of such utensils.
What do you think happens to the scrap alloys collected nowadays. It gets melted, inspected, and modified to the required spec. I doubt it gets made back into saucepans, not pure enough, but plenty good for other specs.
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