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I have heard people talk about the differences between the Rolls Royce Merlins and the Packard Merlins. Is there any obvious way to tell from the outside the aircraft which version of the Merlin this aircraft has? It is a P-51D, AAF sn 44-74009. Were the Packard Merlins used in the later airframes? The "D" model only? Now, this may be a moot point anyway because I am fairly sure this engine,[ch65279] regardless of which Merlin it is, has been worked over by the folks at Roush Racing.

I believe that all production Merlin-powered examples of the P-51 were fitted with the Packard-built engine. That would include your P-51D. There's no telling what the racing specialists get up to. I believe they prefer the Rolls-Royce originals if they can get their hands on them.

PS. The two engines were not interchangeable. The Packard version used some US-built accessories like the starter motor, generator, hoses & possibly fasteners with US standard thread sizes.

I believe that all production Merlin-powered examples of the P-51 were fitted with the Packard-built engine. That would include your P-51D. There's no telling what the racing specialists get up to. I believe they prefer the Rolls-Royce originals if they can get their hands on them.

PS. The two engines were not interchangeable. The Packard version used some US-built accessories like the starter motor, generator, hoses & possibly fasteners with US standard thread sizes.

So then the planes that have the Rolls Royce Merlins would have metric hardware, at least for the engine stuff...?

So then the planes that have the Rolls Royce Merlins would have metric hardware, at least for the engine stuff...?

I would expect Rolls-Royce to use British standard threads like BSW (Whitworth), BSF & BA. I could be wrong but always thought the Packard-built equivalents used US standard threads. I would also expect ancillary components like starter motors & pumps to be of local manufacture. The pipes & flexible hoses fitted to the Rolls-Royce manufactured engines probably have BSP threads & British components would use BA or BSF bolts & screws. If it's an original engine the information you need should be on the manufacturer's data plate.

This is a typical Rolls-Royce data plate.


Compared with the Packard plate.


I believe the rocker covers on British built engines had the name ROLLS-ROYCE engraved on them (see THIS PHOTO) while the Packard versions were plain. This would not be positive identification as the covers could be easily replaced or modified during restoration. Please note that I've never worked on a Merlin & I'm only going from what I've been told over the years.

PS. Just found this. Scroll right down to the bottom. http://www.enginehistory.org/british_fasteners.htm

[quote]

Packard Built Merlins

An often asked question is;

Wow, that is all very fascinating to me. I love historical things like that. So basically Rolls Royce gave Packard the specs for the Merlin and then Packard fabricated or sourced out all the components and built them from scratch or did they get some of the parts (blocks, cylinders, crank, rods, pistons, etc) from RR...? Hmmmmm...

Oh and by the way, thanks a million for your response and info. Much appreciated.

Wow, that is all very fascinating to me. I love historical things like that. So basically Rolls Royce gave Packard the specs for the Merlin and then Packard fabricated or sourced out all the components and built them from scratch or did they get some of the parts (blocks, cylinders, crank, rods, pistons, etc) from RR...? Hmmmmm...

I believe that Packard produced the complete engine. The idea was to set up a separate production line to increase output. Rolls-Royce