Rolls-Royce Merlin Engine Numbers

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Perhaps this is one for Merlin Pete?

Can anyone clarify why the two engine numbers on RR Merlins?

For example, P9374 had a Merlin III numbered 13769 but it also had an A-prefixed number which was 143668.

I have always thought the second number was an RAF or Air Min number (hence "A"?) but would welcome some clarification.

Which was the official engine number - or was one the RR number and 't other an RAF number??

Original post

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14 years 10 months

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I think that is the case. Bristol aero-engines carry two numbers; one from the manufacturer and another from the Air Ministry.

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The best person to clarify the numbers on Merlin's is to speak to Ian at RR Heritage .They have a full listing of every Merlin built and what it was first fitted to he should be able to tell you what is what as they are extremely helpfull.

Mike E

Mike

Thanks.

Yes, I have the full history of the engine already.

Just need to clarify what the two numbers are!! Both are given as engine numbers, but the AM Form 78 for P9374 quotes just one number. I can only conclude one is the RR number and one the RAF numbr.

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Where did you locate the two numbers; on the engine or in the aircraft’s paperwork?

I once tried to confirm that part of a Bristol Hercules engine I had was definitely from a particular aircraft but the ‘loss card’ for the aircraft only listed the Air Ministry number (five digits, starting with a one, no letter prefix) and not the engine number I had (possibly) found stamped on the engine part.

CD

No, both numbers are recorded on the engine plates.

One is shown as the Merlin Engine number, the other as the 'A' number.

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Sorry, our posts overlapped a bit there I think.

Unfortunately I didn’t have the engine plate for my Hercules part; just an engine number stamped on a casting, but the number on the AM Form 78 was the Air Ministry number (similar in format to one of your numbers) not the (prefixed) Bristol one. Not conclusive I know...

...better wait until a Merlin expert lets us know! :o

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"A" numbers are recorded on engines built by all manufacturers, I've certainly always taken it to be a sequentially allocated number issued by the Air Ministry because of that cross manufacturer use. Sometimes both numbers are recorded on 1180s but more often than not it is one or the other number.

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I don’t remember an ‘A’ prefix on the numbers on the AM Form 78 I had but I could be wrong; definitely not a Bristol engine number though.

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Andy.
The A prefix is the Air Ministry contract number, the other is the Rolls-Royce engine numer, which is always an odd number on right-hand rotation Merlins. Both numbers are unique to that particular engine.

Pete

Pete

I knew that you'd know!

Thank you very much indeed. I didn't want to get it wrong when I go to print!!!

You have saved my red face.

Just one query though....

Can you clarify "contract number"? Did this relate to the overall contract for that batch of engines?

Sorry to keep asking questions!

Andy

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The A-number is unique to the engine and was used across the board, so Hercules engines as mentioned would also have a unique A-prefixed contract number.
On paper, the engines were built in batches to Air Ministry contracts which had another number, for example, Merlin III, No 19407 / A144641 was one of a batch of 600 built to contract No 974105/38 (1938), and also an order No 4950, which I think is a Rolls-Royce order number. The only way all these numbers relate is on paper. I don`t know if there is any logic to the AM number stamped on the engine, they appear to have been issued roughly serially, earlier engines have a lower number.
People do sometimes quote the AM number as the "engine number", which is often done on Air Ministry records, but with Merlin engines, the true engine number is agreed to be the Rolls-Royce one.

Pete

Thank you!

You have no idea how helpful that has been.

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The A-number is unique to the engine and was used across the board, so Hercules engines as mentioned would also have a unique A-prefixed contract number.

I don't suppose there is an existing central register that cross-references all these numbers is there?
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I don't suppose there is an existing central register that cross-references all these numbers is there?

Not really, just information that is with Hendon and the PRO at Kew. That`s as far as I am aware anyway.
I think the Rolls-Royce heritage Trust at Bristol may keep production records for the Hercules.
It`s also not usually possible to say which aircraft serial number a particular engine was fitted to, again because there is no database to cross-reference with.

Pete

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Would either of the Rolls-Royce Merlin engine numbers have been marked anywhere else on the engine apart from the engine plate; individual engine components or castings for example?

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Would either of the Rolls-Royce Merlin engine numbers have been marked anywhere else on the engine apart from the engine plate; individual engine components or castings for example?

Yes, both numbers appear on the plate and the port front mounting foot, the Rolls-Royce engine number usually appears in many places. There are exceptions to this, but it's nearly always the case.
The sectioned Merlin Peter Vallance has at Gatwick doesn't appear to have any recognisable numbers.

Pete

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The Hercules seems to have the Bristol engine number stamped on most of the major engine components including the cylinder-barrels and the cylinder-junkheads; pity I haven’t been able to cross-reference that with the Air Ministry number.