New Merlins

168,000, give or take a few; cyl heads may be relatively easy to produce, but they’re not what will be needed, its crankcases, crankshafts, camshafts, reduction gears, and cam covers with “Rolls-Royce” cast into them!

many thanks for the number stuart, i thought it wouldve been much more!

i think there may be one or two manufacturers making Merlin cranks, cams ect already, certainly though crankcases may be a problem, considering how many decent crankcases get grenaded at Reno each year

well i dont think were quite on the verge of a shortage of Merlins yet.

something in the order of half a million were built and many found non-aviation uses after the war, so i doubt we’ll be in trouble for some time yet.

168,000, give or take a few; cyl heads may be relatively easy to produce, but they’re not what will be needed, its crankcases, crankshafts, camshafts, reduction gears, and cam covers with “Rolls-Royce” cast into them!

merlins

I know a historian who a few wees ago, “Santa” visited, and dumped a merlin on his drive, cor wish I had a tooth fairy like that !!, :diablo:

We will run out of petrol, before we run out of Merlins…..

at first thats what i thought but when i sat down a thought about it does that mean the number of merlins in the world is dropping off???
i know even very worn engines can be rebuilt (linning the block and rewelding heads!) but there are cases were some engines are 2 far gone (cracked block, warped heads!) there can only be so many spare blocks and heads knocking about??

well i dont think were quite on the verge of a shortage of Merlins yet.

something in the order of half a million were built and many found non-aviation uses after the war, so i doubt we’ll be in trouble for some time yet.

Living in California there doesn’t appear to be a shortage of Merlins, the place is almost awash with them. I think there were 5 of them in hangar for a while a few weeks back during 2 P51 engine changes.
Roush are making internals & it’s wouldn’t be that big of an engineering exercise to knock out some new heads on a 5axis CNC mill….

Anything can be made for sufficient $$$$;)

Maybe the guy was thinking of zero-timed O/H’d engines?

The tank version (Meteor engine) seems to be quite cheap, I’ve heard about $7K for a runner…

at first thats what i thought but when i sat down a thought about it does that mean the number of merlins in the world is dropping off???
i know even very worn engines can be rebuilt (linning the block and rewelding heads!) but there are cases were some engines are 2 far gone (cracked block, warped heads!) there can only be so many spare blocks and heads knocking about??

does this mean there is a company in the use who is casting new merlin engines?

Nope.

He’s either winding you up, or he’s a plank.

After years of doing it without a second thought assembly and disassembly have always been treated as two processes aimed at achieving a goal, you apply the same process in reverse to take the shaft caps out of the motor as you do too put them in, this way you avoid any chance of distortion or stress in either the caps or the studs, I have seen more than few broken in my time, mostly while trying too slacken cap stub nuts off in prepration for seperation, they are a pig too drill out and re-tap for new ones as they almost invariably break 2 mm below surface, it,s time consuming and bad practice on the part of the engineer to try and get around this process by using short cuts however using a dial gauge is a little extreme, a simple torque plate is all thats required and any engineer worth his salt could knock one up in a few minutes marked off in degrees to assist in disassembly.

In one of the RR service manuals, it describes undoing the main bearing nuts to remove the crankshaft, the procedure requires a dial gauge to be located on the main bolt stud, and to slacken off a few thou at a time on each bolt (in a set order); I can just about understand the need for a dial gauge on assembly, but disassembly….

Possible distortion of the cap, it’s not unusual to have rather solid looking assemblies distort if they are dismantled wrongly.

How about Casa built examples?

(sorry for throwing a spaniard in the works…:rolleyes: )

& I’ve seen “Buick” cast into Merlin cylinder blocks in the US….

drawings

I think it was just Ford updating the drawings to bring them online with the rest of their manufacturing lines.They were one of the leading mass manufacturers of the early 20th century.The merlin is a complicated engine by American standards and I always thought it was the metallurgy that wasn,t as good as the RR counterparts.I think Damiler was better at close tolerances than RR during the early part of the war.

In one of the RR service manuals, it describes undoing the main bearing nuts to remove the crankshaft, the procedure requires a dial gauge to be located on the main bolt stud, and to slacken off a few thou at a time on each bolt (in a set order); I can just about understand the need for a dial gauge on assembly, but disassembly….

All aero engines everywhere were more or less hand-built prior to the late 30’s when manufacturers geared up for mass production. In order to get the volumes necessary to meet demand, and to be able to use a less skilled workforce meant producing drawings that allowed less deviation from the nominal dimension…

Some manufacturers were ahead of others, Allison and Bristol engines were certainly designed for mass production with completely interchangeable components early on. I’m not sure about other manufacturers but, as you say, the key thing here may be the volumes produced (for the RAF), particularly pre-war, and the number of (British, military) engine manufacturers.

I tend to think that buried deep in th RR folklore, there are some truths, I do wonder given RR’s eliteist nature , whether the re drawing issue, wasn’t “payback” from companies (such as Fords UK), that hither to, RR would have had no truck with.

Yes, I think it speaks volumes that Rolls-Royce assumed that ‘humble’ Ford wouldn’t be able to meet their tolerances!

With regard to the tightening up of tolerences, clearly, closing up any running clearances wouldn’t have been acceptable…

Agreed, but tightening tolerances makes this less likely.

I have heard it said that RR engine builders never used a torque wrench, instead relying on their experience of bolt sizes and just how tight they should be…

I can well believe that, there are probably relatively few bolts on a Merlin where the torque is critical and torque wrenches need careful handling to ensure accuracy.

I tend to think that buried deep in th RR folklore, there are some truths, I do wonder given RR’s eliteist nature , whether the re drawing issue, wasn’t “payback” from companies (such as Fords UK), that hither to, RR would have had no truck with.

With regard to the tightening up of tolerences, clearly, closing up any running clearances wouldn’t have been acceptable; I have heard it said that RR engine builders never used a torque wrench, instead relying on their experience of bolt sizes and just how tight they should be , obviously that would be a recipe for disaster, with an unskilled workforce, but that merely needs a spec sheet drawn up (and adhered to!)

For the sake of argument, if Ford (UK) built a Merlin and some (or all) of the Ford tolerances were ‘tighter’ than the Rolls-Royce tolerances, then the Ford Merlin would fit together and run perfectly without the need to modify anything else on the drawings…

…also any part of the Ford Merlin could be used as a spare part on a Rolls-Royce built Merlin. The Rolls-Royce parts could not be guaranteed to fit the Ford Merlin however.

But if Rolls-Royce were ‘hand-building’ the Merlin and selectively fitting parts together (or modifying parts out of tolerance) then this would not necessarily be the case.

I suspect what we have here is not an issue of tolerances alone but a rather more complex situation regarding the differing working practices, drawing standards and workforces employed by Rolls-Royce, Ford and Packard.

All aero engines everywhere were more or less hand-built prior to the late 30’s when manufacturers geared up for mass production. In order to get the volumes necessary to meet demand, and to be able to use a less skilled workforce meant producing drawings that allowed less deviation from the nominal dimension, which for many components on the Merlin did not alter from first to last. Perhaps today we read too much into the tolerances between RR and the shadow manufacturers. It certainly adds intrigue if nothing else.

Engineering Tolerances

…begging the question, if both Packards and Fords (UK) had to redraw the Merlin (because the original RR tolerances were too wide) why does it all fit?

For the sake of argument, if Ford (UK) built a Merlin and some (or all) of the Ford tolerances were ‘tighter’ than the Rolls-Royce tolerances, then the Ford Merlin would fit together and run perfectly without the need to modify anything else on the drawings…

…also any part of the Ford Merlin could be used as a spare part on a Rolls-Royce built Merlin. The Rolls-Royce parts could not be guaranteed to fit the Ford Merlin however.

But if Rolls-Royce were ‘hand-building’ the Merlin and selectively fitting parts together (or modifying parts out of tolerance) then this would not necessarily be the case.

I suspect what we have here is not an issue of tolerances alone but a rather more complex situation regarding the differing working practices, drawing standards and workforces employed by Rolls-Royce, Ford and Packard.

There’s an article in one of the Warbirds World Wide issues about the redrawing of the Merlin information before putting it in production by Packard.
Isn’t it that the differences between the British and American engines are in the accessories? Pumps, carburettors etc?

Cheers

Cees

I think you are correct here. I have read this also I believe in one of the RR heritage books. The fact that the engine was redrawn has often been miss-interpreted as it was “Americanised” or “Metricated”, when in fact it remained identical.

Ford did redraw the Merlin. (Sir) Stanley Hooker said they came to him saying they couldn’t build them because the tolerances were too wide. He had expected the opposite reason. 🙂
In his words “it took them a year and after that they came out like shelling peas, and very good engines they were”.

From “Not Much Of An Engineer”.

I find it hard to believe Packard engines were AF as opposed to BSW/BSF when they’d gone to all the trouble of making British taps and dies.
I’ve heard before that the Packard toolkit was extremely comprehensive and of superb quality compared to what came with a Rolls-Royce engine.

I agree, after speaking to a reliable source at RRHT this evening, Ford certainly did redraw it, sorry!
As per my previous post, Packard Merlins share the same BSF and BA threads as Rolls-Royce engines, but most of the specialist tools I have come across are indeed different to the British ones, so they designed these themselves with little reference to what we had I suppose. All our Packard tools have an AT prefix which does not appear on R-R tools.

It is a BIG subject 😉

Pete

Ford did redraw the Merlin. (Sir) Stanley Hooker said they came to him saying they couldn’t build them because the tolerances were too wide. He had expected the opposite reason. 🙂
In his words “it took them a year and after that they came out like shelling peas, and very good engines they were”.

From “Not Much Of An Engineer”.

I find it hard to believe Packard engines were AF as opposed to BSW/BSF when they’d gone to all the trouble of making British taps and dies.
I’ve heard before that the Packard toolkit was extremely comprehensive and of superb quality compared to what came with a Rolls-Royce engine.