Rolls-Royce Merlin Engine Numbers

Amen to that P&P.

Oracal, thank you for the Bristol Aerospace reference.  Thank God for people who save things from rubbish bins! Eternal damnation for tidiness freaks that throw everything out! May hell for them be an eternity in a compulsive hoarders basement!  

Thanks Oracal, mmm strange as it’s definitely a merlin block, i’ll double check the number 

Hi P&P. 

Thank you for that info. The AID instruction regarding engine number stamping was published during the 1930s, but my evidence shows it had been going on since at least 1926.

To quote RR Heritage;

“The master registers of engine numbers was held and maintained by the contemporary ministry. The engines given in the following listing are from the volume covering the period 1918 to 1963. This was rescued from scrapping by MoD employee Tim Mason; sadly the previous volume(s) were not saved, making it unlikely that a fully complete 
listing of all ministry numbers allocated to military engines will ever be known. 

The Rolls-Royce Heritage Trust considered the book to be of such historical value, and recognising its worn state undertook to have its pages digitally scanned to ensure that its contents were preserved in an accessible format.”

Yes, the Dagger and Kestrel engines are listed.

I obtained my copy on CD c/o Aerospace Bristol. It has their reference no: KEM PH/CD/17 . The price was £10, but that was a few years ago.

Oracal, I can concur thar RR practice was to repeat its engine number an the AM Axxxxx number on the port front foot of RR Kestrels. Napiers repeated their engine number on the port front side of the crankcase, also repeating the AM Axxxxx number on Daggers, so it seems this was Service Contract practice from the prewar. Not sure if the system persisted in the later war years, but hopefully your AM list will illuminate this aspect with more clarity. Does this list include Kestrels and Daggers? 

Re numbering of AM and manufacturers number on an engine. There was an A.I.D requirement that the manufacturer’s engine number was required to be stamped on the crankcase. Anecdotally, I have seen it it placed on the forward port side of the crankcase and aft of any propeller gearbox. I have seen the Air Ministry number stamped on the manufacturers engine plate and usually, but not always, proceeded by an ‘A’ – eg A194403, a Pobjoy R [#133] impressed by the Air Ministry during WW2, and now fitted to the Comper Swift at RAF Cosford. 

Anonymous (if you’re still here). “For example, P9374 had a Merlin III numbered 13769 but it also had an A-prefixed number which was 143668.”

[AM] 143668, a Merlin III, one of 200 built to contract 819222/38.

Hi Booomer. 

I have a copy of the Air Ministry list of engine numbers and looked up the details recorded for “307101”. According to the official list you have part of a Bristol Hercules VI, one of the 3,000 ordered under contract B. 33820/39. 

However, had it been 317101 …

My boss has a merlin block that has been made into the mother of all coffee tables and bears the serial number 307101. Just wondering if anybody could shed any light on it’s history. 

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.

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

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?

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

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?

Thank you!

You have no idea how helpful that has been.

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

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

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

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.

“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.