Which country designed the best engines for WWII?

[Reluctant Poster]

Yes, they did laboriously hand lap the surfaces, and they were oil tight - only once.
As soon as they got out in the field and mechanics did what mechanics do, open up this hand fitted faces regularly, lever open faces with screwdrivers, they leaked like sieves for ever more.

It was a basic failing - Rolls Royce were not production engineering the engines as a mass market commodity.

Packard engineers took one look at a Merlin, burst out laughing and redesigned it like a car engine. Gang milled every surface and chucked a paper gasket in it, built them much faster, much cheaper and much easier to maintain.

Nonsensical Packard did not redesign the Merlin, they merely redrew it to American conventions. There have been plenty of discussions in this forum debunking this myth. Show us your comparative data for speed, cost and maintenance

 

[Reluctant Poster]

Part of Hooker's story was he was sitting in his office (shared with another RR official) when one of the men from Ford came in and said they could not build engines with the tolerances listed on drawings. Hooker asked if that was because Ford could not maintain the tolerances. (a bit being a snob about it as he explains in his auto-biography) The Ford man said no, it was because Ford needed much tighter tolerances in order to assemble engines using interchange parts.
You don't build cheap cars in quantity using semi-skilled labor and stay in business otherwise.

That said the Merlin needed pretty tight tolerances for it to work. Any high performance aircraft engine did. But the tight tolerances needed to be specified on the drawings to being with and maintained through manufacture of the parts and through dozens of inspections so that when the parts reach the assemblers 99% (or better) of the parts will fit together with no fitting or selecting. Selecting pistons and con rods gets a bit tricky as each assembly and each group of 12 pistons/con rods has a certain weight tolerance. You don't sit there and "file to fit" it the piston/con rod is too light or heavy it gets put aside and another one is weighed and if it "fits" with the group it is used. When you get enough light (or heavy) piston-con rod assemblies to make a complete engine you can assemble a light or heavy crankshaft assembly and put that in an engine. All the piston-conrod assemblies had a certain weight range they had to fit in in relation to the 12 cylinders used. However the total range of possible weights was larger.

A complete pair of assembled rods, pistons, pins and rings in an engine had a permissible variation was 1 oz. for Merlin II.
Permissible variation of pistons selected for one engine was 1/2 oz.
Permissible variation between any two pairs of connecting rods, pistons, pins and rings fitted to one engine was 1 oz.


There was a considerable amount of fitting/selecting even so, but the stories of "filing to fit" are not true.
The better the manufacturing and in a lot of cases that means better inspection, the more parts that make it to the fitters are in tolerance, and require less selection.

Tolerances are from "Aircraft Handbook" by Fred Colvin 1942 edition section III.

People that tell tales about loose tolerances or how engines were assembled need to look at handbooks that describe actual tolerances and how the engines were torn apart and reassembled. The book has 37 pages on overhauling a Merlin II had is pretty much "guidance" for a man who has gone to school to learn all the basic techniques.
Even with the book I am no more qualified to rebuild a Merlin engine than I am to launch a moon rocket.

The following video of Ford River Rouge pre WWII shows that Ford weighed not just each piston but each piston connection rod assembly. Start at the 18.00 mark

 

[Reluctant Poster]

One other issue is that a minute scratch on that perfect mirror finish is likely to seriously degrade fatigue life, much worse than a similar scratch on a normally finished surface.

From "The Merlin in Perspective":
"Because Packard were less flexible in embodiment of modification, engines from this source used the Mod 399 rod for much longer and ran into a number of characteristic failures. When examined the Packard rods appeared to be well finished with heavy polishing of the radius and associated areas. British experience was that rods free of finishing scores were far less prone to failure and this apparent contradiction was surprising. however , when rods were etched it was found that the polishing operation had swaged material into deep score marks , masking them from visual inspection, and failures could therefore be expected. it was a lesson in the effect of heavy over-polishing."

 

[pbehn]

Urban Legend. Early Merlins leaked glycol before the change to pressurized water cooling. Packard Merlims were all built after the change.

That was in the early days, some Derby housewives mistakenly used greaseproof paper reserved for Christmas cakes for gaskets, a memo with a bunch of flowers sorted it out.

 

[tomo pauk]

Really funny how R Reluctant Poster tries to put the facts ahead of the bed stories.

 

[Shortround6]

Urban Legend. Early Merlins leaked glycol before the change to pressurized water cooling. Packard Merlims were all built after the change.

Most (all ?) of the engines that used 100% glycol leaked. 70/30 solved a lot of glycol leak problems for engines that used it.

 

[Deleted member 68059]

Most (all ?) of the engines that used 100% glycol leaked. 70/30 solved a lot of glycol leak problems for engines that used it.

Pure Glycol has very low surface tension, so it just goes through gaps like they`re not there.

 

[Reluctant Poster]

Nonsensical Packard did not redesign the Merlin, they merely redrew it to American conventions. There have been plenty of discussions in this forum debunking this myth. Show us your comparative data for speed, cost and maintenance

For those are are genuinely interested in how Packard actually built Merlins here is an excerpt from Fedden's mission to America:

While I'm at it here is the Mission's appraisal of Allison:

 

[Reluctant Poster]

From "The Merlin in Perspective":
"Because Packard were less flexible in embodiment of modification, engines from this source used the Mod 399 rod for much longer and ran into a number of characteristic failures. When examined the Packard rods appeared to be well finished with heavy polishing of the radius and associated areas. British experience was that rods free of finishing scores were far less prone to failure and this apparent contradiction was surprising. however , when rods were etched it was found that the polishing operation had swaged material into deep score marks , masking them from visual inspection, and failures could therefore be expected. it was a lesson in the effect of heavy over-polishing."

Here's an excerpt from the Fedden mission to America on Allison conrods:

 

[special ed]

For those are are genuinely interested in how Packard actually built Merlins here is an excerpt from Fedden's mission to America:

View attachment 665520

While I'm at it here is the Mission's appraisal of Allison:

View attachment 665521
View attachment 665522
View attachment 665524

Who was Col. Vincent?

 

[Deleted member 68059]

Who was Col. Vincent?

Possibly ?

J. G. Vincent
Vice president of engineering
Packard Motor Company.

 

[special ed]

One assumes:

J. G. Vincent
Vice president of engineering
Packard Motor Company.

Many thanks.

 

[wuzak]

Most (all ?) of the engines that used 100% glycol leaked. 70/30 solved a lot of glycol leak problems for engines that used it.

Pure Glycol has very low surface tension, so it just goes through gaps like they`re not there.

Weren't there also sealing issues with the sleeves inside the single piece blocks, hence the move to a separate head design?

 

[Reluctant Poster]

Weren't there also sealing issues with the sleeves inside the single piece blocks, hence the move to a separate head design?

You are correct. From The Merlin in Perspective by Alec Harvey-Bailey:

"External coolant leaks at the base of the cylinder block were overcome by Mod 231 which provided a triple seal ring instead of a single bootlace seal.
A picture tends to be painted of single piece block engines with top joints leaking like colanders and being a risk to the pilots . In fact most engines did not have blocks changed for leaks in the course of a normal life and when engines were pulled for leaks, their total was not a major cause of engine removals, although probably in the top 5. The leaks tended to be more prevalent in fighter operations where engines were subjected to constantly changing conditions."

 

[Reluctant Poster]

PT boats did not use Rolls-Royce engines; they used a marine derivative of a Packard engine designed before the Merlin

Actually, the prototype for the Elco boats was PT-9 which was built in England as British Power Boats PV70. It was powered by three marinized Merlins.

From "The Magic of a Name" by Harold Nockolds.
"The fame of the Merlin was already extending beyond aviation circles, and in the years immediately before the war Rolls-Royce was asked by Power Boats, Ltd., to co-operate in producing a high speed motor torpedo boat in which they planned to fit three Merlins. It proved quite simple to adapt the engine for marine work- the power output was adjusted to suit the different operating conditions, the airscrew reduction gear was removed, a special air intake was fitted, and a salt-water cooled heat exchanger was added to allow the engine to retain the normal fresh water in the cylinder jackets, pipes and circulating pumps. The Merlin was as successful in this new element as it was in the air, and the prototype M.T.B caused immense enthusiasm by averaging almost exactly 60 m.p.h. in a trial run from Southampton to Cherbourg. The Admiralty ordered a large number of theee boats, which were to give splendid service in various theaters of war, but when hostilities finally broke out the Government instructed Rolls-Royce to drop all marine work and concentrate on making engines for aircraft."

The prototype mentioned was British Power Boats PV70 which was the template for the BPB MGBs used by the Royal Navy, but also was sent to the United States where it became PT9.
Quite a few of the early BPB boats were powered by Merlins as this site lists.
Motor Gun Boats – Spitfires of the Sea
As an aside Vosper's pre war boats used Isotta –Fraschini engines which were twice the displacement of a Merlin

 

[Shortround6]

As an aside Vosper's pre war boats used Isotta –Fraschini engines which were twice the displacement of a Merlin

The displacement doesn't actually matter.

It is interesting but too many of us have been indoctrinated into assessing engines by displacement due to car and motorcycle racing rules.

Things that matter more for practical use are the weight per hp and volume of the engine (space occupied by the engine) per hp.

There were no rules for engine displacement in war planes and there none for MTBs.

The W-18 Isotta-Fraschini engines were within a few hundred pounds of of the Merlin, this depends on supercharger and reduction gears although a marine Merlin needs a new gear box.
In high speed boats the max continuous power (1 hour or 4 hours or 8 hours) was often more important than max peak power or a 5 minute rating.

 

[Deleted member 68059]

I think I`ve already nailed this coffin shut, but for the notion of British "hand finished" aero-engines in WW2, this I hope adds the full treatment of exhumation and burial at sea.

 

[Deleted member 68059]

and for good measure, I just found this memo about Parkard-Merlin / RR Merlin spare parts interchangeability.

Whilst certain parts of the letter are illegible, its obvious that there is no engineering difficulty in fitting of either.

Its almost as if, there was no difference at all in the tolerances... well I never. (actually I already knew this perfectly well
but just didnt have a letter proving it).

I suspect the letter reads:

"Mr Sidgreaves mentioned the interchangability of Packard/Merlin spares, and it was agreed that it might be
these should be used in the repair of Rolls Royce engines so certain Dominions should be supplied with Packard
items from America in lieu of Rolls Royce made items. It was pointed out, however, that this would still leave the same quantity
of these items to be delivered by Rolls Royce because even the Packard engines in this country might have to be fitted with
Rolls Royce made spares. In other words, whatever comes from the stock of Packard items would eventually have to be produced
and repaid, so that the repair of Packard engines need not be prejudiced."

Letter is dated 25th May 1943

 

[GrauGeist]

Just out of curiosity, what was the cost comparison between a Packard Merlin and a Rolls-Royce Merlin?

And I am asking about a complete turn-key engine, ready to be installed.

 

[Deleted member 68059]

Just out of curiosity, what was the cost comparison between a Packard Merlin and a Rolls-Royce Merlin?

And I am asking about a complete turn-key engine, ready to be installed.

I dont know ! (if/when I find documentation I will post here)