I do think and i stress think, you are quite right. But....thinking is not facts in this case.
And you do not bring them. Logical yes. Facts no.
Please provide a source thats supports your thinking.
The Merlin production figures for each plant are so well known they`re all neatly listed even on Wikipedia.
Rolls-Royce Merlin - Wikipedia
As for my confidence in my assertions, I have been to Rolls-Royce Derby archives, Rolls-Royce corporate archives, Rolls-Royce Bristol archives, and
read all the personal correspondance of Ernest Hives himself - and in addition been invited to lecture at Rolls-Royce about the German
opinion of the Merlin engine.
So I dont have any time for nonsense history like that article.
The notion of each engine from Britain being some sort of cobbled together junk-heap with each bit fettled to fit is dispelled by a simple mathematics
excersize in looking at the number of engines, and the time in which they were built. Everything in Britain from about 1940 onwards was being mass produced,
if it hadn`t been, there`d have been no Merlins, during the Battle-of-Britain every single Merlin came from one production line at Derby, as the output
from the other factories (also RR run) hadnt come online yet.
I would imagine that a lot of hand fettling happened in Britain, as we were getting bombed, and the Merlin needed a lot of early modifications to cure
all sorts of defects, so changes would have been happening constantly. But this is all totally misrepresented by one quote about tolerances, which
has been used to create a historical nonsense. In addition most repairs and modifications were made by RR to each engine when they came back
to the factory for a rebuild. The whole system was exceptionally well organized and RR had total control, when the RAF tried to have their people
take care of the engines, Hives overruled the Air Ministry and said he would only supply engines if RR had full control of field servicing by RR
personell. These people imagining the British at the time were bumbling about like simpletons have no idea. RR had an utterly ruthless grip on aero
engine design, manufacture repair and servicing from start to finish - to an extent which in some respects makes the Germans appear amateurish
(that doesnt meant I`m suggesting the Americans were less professional, I`m simply stating that saying Packard were wonderfully professional
and did a marvellous job DOESNT mean the Brits were floundering about like blind lambs.
The number of sub-contractors supplying Merlin bits for all the RR run factories in England also shows the "hand fitting" story to be nonsense,
all these shadow plants and suppliers would never have time to get hundreds of rejects sent back, and would have been fined and lost their
contracts. They managed to do all this because they all had proper drawings whereby people with no aero engine experience whatsoever
could make Merlin parts. How it is imagined that this all happened by any other means is a total mystery to me.
I also happen to have all the Merlin reliabilty data, and it shows he RR built engines to be excellent, again, making a nonsense of how
else 80,000 Merlins were somehow all "hand-made" by magic, when Packard needed a perfect production plant operating like a swiss
watch to make 55,000. Quite obviously, both firms did a world-class job of mass producing their variants, the Packard effort being
impressive as they made many improvements and did so without the expereince of RR staff at as close a hand as they were in Britain.
As for the tolerances, Available at Kew National Archives in London
AIR-10/2175 "Merlin-I Fits and Clearances October 1938"
Merlin I Aero-Engine: Part II Schedule of Fits, Clearance and Repair Tolerances | The National Archives
Even in 1938 the Merlin crank (for example) had a limit on the journal diameter of +/-0.00025 of an inch,
and the tolerance stack on the clearance was 0.75 thousandths.
This is not far off modern automotive steet tuning best practice.
https://www.mahle-aftermarket.com/media/local-media-north-america/pdfs-&-thumbnails/cl77-1-205r.pdf (Mahle Powertrain / Clevite are one of the worlds largest
manufacturers of automotive crank bearings today)
"Let's pick some typical manufacturing tolerances and look at the potential clearance range that results. A tolerance range (from min. to max. sizes) of .0010" is typical for most crankshaft journals"
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So let me condense that down. A Merlin Crank from 1938 in Britain, before the production even really got started had a crank journal diameter grind limit 50% tighter than a current automotive production car engine (mahle document dated 2005, so: 67 years later.....we`re half as good 1938 Merlin.).
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A page from the Merlin XX "fits and tolerances" manual dated May 1945.... its the same. So apparently no improvement was needed either....although the clearance has been cut a bit
all the tolerances remain identical from the Merlin-1 in 1938 to 1945.
Source:
Merlin XX, 21, 22, 22A, 23, 23A, 24 and 25 Aero-Engines | The National Archives
I`m not suggesting that Packard didnt change any tolerances to suit themselves, but I am proving that its utter nonsense to suggest that even the Merlin-I wasnt toleranced to a level necessary for mass production, even by todays standards.
We can also compare to Daimler-Benz DB600 series, with the German reputation for prescision, the DB605 crankshaft drawing for example shows
the crank main bearing journal grind tolerance at +/- 0.0004"
So the 1938 Merlin-1 crank journal grind limit is also not only better than a modern engine but tighter than a Daimler-Benz.
Before anyone says "yea but wartime Germany..." thats the same tolerance as the Swedish licence drawings for the DB605 dated November 1945 (which
are not DB drawings, but entirely redrawn).
(Kurbelwelle = Crankshaft)
"D" is the crank journal diameter, and its 100mm g6, which you can look up in the table at the end, its in "mm" so you`ll have to convert.... -0.034 -0.012mm = 0.022mm delta
= 0.022/25.4 = 0.00086" = +/- 0.00043"