An interesting read about the Packard built Merlin engine.

Shortround6 · Jan 4, 2020

As usual there may be both elements of truth and elements of "not truth" in some of these positions.
Ford car engines were made of cast iron and would probably take a much higher level of abuse in assembly than an engine made of Aluminium. I had an Oldsmobile for a while that used an aluminium engine (later sold to Rover) and some friends that worked on American cars were astounded at the torque ratings on the head bolts compared to American. It was almost 50 years ago so I forget what the exact settings were but the Aluminium engine head bolts were torqued to a much lower setting than head bolts going into an iron engine.
I would also note that there may be a world of difference between an air tool used on an assembly line (more carefully adjusted or regulated?) and the ones used by tire changers at the local tire shop (I have broken several studs trying to remove a flat tire that was air wrenched on, that or the stud was already stretched/fractured?)

Point in bring up the weight of the piston-rod set was not to claim that RR was doing something others were not but to bring up that it might have been possible for a file to be used in some instances (like helping to lighten up one or two pistons out of 12) but not anywhere near most parts being filed to fit.
The whole filed to fit thing is fabrication as any file marks on any highly stressed part is a fatigue crack just waiting to start. Most parts. like con rods were highly polished and any blemishes could cause the part to rejected at inspection, well before assembly and there isn't a whole lot you can do with a file to adjust the fit of a con rod or crankshaft.

Also note that an American Ford 85-95hp Ford Flathead V-8 weighed about 525lbs or more than a 200hp DH Gipsey six engine or about the same as a Lycoming 9 cylinder R-680 225-300hp radial engine.

Tolerances for easy manufacture they may have had, but the margins of error in metallurgy and assembly were huge compared to even small aircraft engines,

Deleted member 68059 · Apr 30, 2020

Snowygrouch said:
Sorry update to issue, someone elsewhere pointed out that the Torque wrench part number was post-war, and it seems that booklet was re-printed in Nov 1945. So here is another Merlin manual page from 1944 to confirm wartime usage.

Here is page 189 from the Merlin-II Handbook, dated May 1938.

It seems that in that date they did NOT use torque wrenches.... they used "torque-slipping spanners"

In this very early manual, there ARE other bolts which are left in the manual as "by hand using a special spanner" (i.e. one with a tiny handle so you cant apply a gigantic torque and strip the threads), so I suspect this whole thing probably started off with taking what was done
in 1938 prewar condition before any of the shadow/licence factories were working on some less critical bolts and then taken as "thats what RR did for everything on the Merlin".

fastmongrel · Apr 30, 2020

Isnt the torque-slipping spanner a device to torque a fastener down to a set poundage. A torque wrench on the other hand is a device to torque a fastener down to a set poundage.

Tomato or Tomato I think.

pbehn · Apr 30, 2020

fastmongrel said:
Isnt the torque-slipping spanner a device to torque a fastener down to a set poundage. A torque wrench on the other hand is a device to torque a fastener down to a set poundage.

Tomato or Tomato I think.

Such things happen, I once worked on a project where the specification required SSCC (Sulphur Stress Corrosion Cracking) and "4 point bending" tests. In fact they are exactly the same test which confused the hell out of QC coordinators who deal in names and numbers only. For literally years various people talked about "Battelle" tests and "DWTT Drop Weight Tear Tests" when they are one and the same. A throwback to the war years is that a standard impact test in the English speaking world is a "Charpy test" whereas Mr Charpy was a French metallurgist, In France and most other European countries it is called by a description an Essai de resiliance, Prove de resiliance, kerbschlagbeigeversuch or other.

Reluctant Poster · May 1, 2020

Snowygrouch said:
Here is page 189 from the Merlin-II Handbook, dated May 1938.

It seems that in that date they did NOT use torque wrenches.... they used "torque-slipping spanners"

In this very early manual, there ARE other bolts which are left in the manual as "by hand using a special spanner" (i.e. one with a tiny handle so you cant apply a gigantic torque and strip the threads), so I suspect this whole thing probably started off with taking what was done
in 1938 prewar condition before any of the shadow/licence factories were working on some less critical bolts and then taken as "thats what RR did for everything on the Merlin".
View attachment 579459

I like the reference to "the convenience of the foothold which he may have". Anyone who has ever worked on a Volkswagen FWD will understand.

MIflyer · May 3, 2020

One aspect of Merlin manufacturing I have wondered about is the definition of "quality." I don't think anyone would disagree with the idea that RR had better "quality" than most or all other companies, but how do you define it?

One of my college Masters professors flew P-51's and WWII and he said you could tell the difference between the RR and a Packard Merlin. He said the RR was much smoother, a consequence of the RR "craftsman" approach that they apparently are using even today. The pistons in each RR built Merlin were hand selected during assembly in order have them near the same weight.

When I was part of a DoD group that did a study of the MCAIR factory at St. Louis, we visited a local subcontractor factory. They said they were highly committed to quality. I asked them if "quality" meant taking a part specified to have a 125 finish and instead making it a 60 finish. The reply was no, that would cost too much. But there are people who would consider making a 60 finish where a 125 would do an example of better quality. In fact there was a famous case where RR did just that. Needing an electric starter, they purchased a Delco example along with the manufacturing rights and built their own version - which did not work. It turned out that RR had looked at the rough cast finish of a part of the Delco starter and decided they could do a lot better than that. But the rough cast finish of that part was a design feature, part of a clutch arrangement and needed to be rough. The "quality" was better, at least according to one definition, but the component did not work.

When RR first introduced automobile companies to the Merlin they got complaints that they could not build the parts to the tolerances specified on the RR drawings. Stanley Hooker asked if the tolerances were that much tighter than what the auto companies could do. The response was no, the problem was the RR tolerances were too loose! The automotive approach was to make the parts so close that the engine could be built by minimally skilled workers on a production line. So if Packard had to build Merlin parts to tighter tolerances than RR did, who had the better "quality?"

buffnut453 · May 3, 2020

MIflyer said:
One of my college Masters professors flew P-51's and WWII and he said you could tell the difference between the RR and a Packard Merlin. He said the RR was much smoother, a consequence of the RR "craftsman" approach that they apparently are using even today. The pistons in each RR built Merlin were hand selected during assembly in order have them near the same weight.

And here we go back to "RR Merlins were built by craftsmen with each part hand-selected and/or fettled to fit." There have been several threads on this myth. It would be impossible for the Merlin to be mass-produced if individual components were hand-picked on the production line. As others have pointed out, Merlin mass-production had been ongoing for a considerable time before Packard even saw a RR drawing.

Most pilots who flew Merlin-engined aircraft had no clue about where, when or how the engine in their aircraft was made. Given the well-known interchangeability between RR and Packard units, I find it really difficult to believe that a pilot would know from sound who made a particular engine.

MIflyer said:
In fact there was a famous case where RR did just that. Needing an electric starter, they purchased a Delco example along with the manufacturing rights and built their own version - which did not work. It turned out that RR had looked at the rough cast finish of a part of the Delco starter and decided they could do a lot better than that. But the rough cast finish of that part was a design feature, part of a clutch arrangement and needed to be rough. The "quality" was better, at least according to one definition, but the component did not work.

Do you have something more definitive than hearsay on that story? I find it hard to believe that RR would take a component from a supplier, buy the rights to it and then produce it on their own. That doesn't make financial or logistical sense when you could just buy the component from the supplier. I can search online auction houses and find Delco-stamped starters for use on RR vehicles so, clearly, at some time RR just ordered direct from Delco.

Please provide evidence of this story.

And here we are

MIflyer · May 3, 2020

I read that story about the RR starter over 50 years ago. It would have happened before 1920 and I find it all too believeable that they would have built their own rather than buy starters imported from the US.

buffnut453 · May 3, 2020

MIflyer said:
I read that story about the RR starter over 50 years ago. It would have happened before 1920 and I find it all too believeable that they would have built their own rather than buy starters imported from the US.

I really don't care what you find believable. I'd like to see evidence before making any kind of judgement. There are too many hoary old chestnuts related to RR and the Merlin that get trotted out with monotonous regularity but seldom with any actual proof.

RR announced that all cars built after the end of WW1 would have an electric starter so, if your story is correct and happened pre-1920, it would be in a very short time period in 1919. Again, you're the one making the claim so please provide evidence to back it up.

Reluctant Poster · May 3, 2020

I am reminded of one of Strother Martins many great lines from "Cool Hand Luke". "Some men you just can't reach."
Snowy Grouch and Shortround have produced reems of documents showing that Merlins were not hand built, I guess the anecdotes are more entertaining and support preconceived notions.
For the record Rolls Royce was buying components from the US in WWI for the Eagle.
When RR started production in Springfield MA in 1920 they initially used British components but soon switched to American ones such as Bijur starters and Bosch magnetos. Royce thought they were better quality than Lucas. In fact in general RR liked CAV components over Lucas.
For the Merlin itself RR began importing components from the US early in WWII. Crankshafts are one such component.

pbehn · May 3, 2020

MIflyer said:
When RR first introduced automobile companies to the Merlin they got complaints that they could not build the parts to the tolerances specified on the RR drawings. Stanley Hooker asked if the tolerances were that much tighter than what the auto companies could do. The response was no, the problem was the RR tolerances were too loose! The automotive approach was to make the parts so close that the engine could be built by minimally skilled workers on a production line. So if Packard had to build Merlin parts to tighter tolerances than RR did, who had the better "quality?"

I believe that anecdote was reported by Hooker in a book, it was actually Lovesay that said it. RR was an automobile company itself (Mr Rolls was a car dealer and Mr Royce a car maker) and had been in contact with many companies for years. As far as the Merlin is concerned I believe they were in talks with Ford of France and UK about production. Lovesay was not a production engineer, he was a development engineer. At the time that the conversation took place his main experience had been with the Schneider trophy engines and setting up flight testing. He may well have just been trying to be polite and conversational. The R engine he was involved in in the racers must be the ultimate in low quantity production only 19 were made. When you are making an engine at such low numbers maybe you do machine one set of parts and then machine others to fit like barrels and pistons.

Reluctant Poster · May 3, 2020

pbehn said:
I believe that anecdote was reported by Hooker in a book, it was actually Lovesay that said it. RR was an automobile company itself (Mr Rolls was a car dealer and Mr Royce a car maker) and had been in contact with many companies for years. As far as the Merlin is concerned I believe they were in talks with Ford of France and UK about production. Lovesay was not a production engineer, he was a development engineer. At the time that the conversation took place his main experience had been with the Schneider trophy engines and setting up flight testing. He may well have just been trying to be polite and conversational. The R engine he was involved in in the racers must be the ultimate in low quantity production only 19 were made. When you are making an engine at such low numbers maybe you do machine one set of parts and then machine others to fit like barrels and pistons.

Hookers biography "Not much of an Engineer"
I would also point out the title is self explanatory. Hooker was a mathematician not an engineer. He was at that time responsible for the theoretical aspects of one part of a very complex engine. He was not involved in the design or production of the Merlin save for the supercharger.
He has attained deity status unjustly in my opinion, there is much more to the success of the Merlin than the worlds best supercharger (which i am not denying). Note that one of the keys to the Hooker designed supercharger was the central entry which RR was testing before Hooker joined the company.

pbehn · May 3, 2020

Reluctant Poster said:
Hookers biography "Not much of an Engineer"
I would also point out the title is self explanatory. Hooker was a mathematician not an engineer. He was at that time responsible for the theoretical aspects of one part of a very complex engine. He was not involved in the design or production of the Merlin save for the supercharger.
He has attained deity status unjustly in my opinion, there is much more to the success of the Merlin than the worlds best supercharger (which i am not denying). Note that one of the keys to the Hooker designed supercharger was the central entry which RR was testing before Hooker joined the company.

Oh there were many people involved but Hooker did study hydrodynamics and aerodynamics and got a PhD.

Reluctant Poster · May 3, 2020

pbehn said:
Oh there were many people involved but Hooker did study hydrodynamics and aerodynamics and got a PhD.

And that was a testament to the genius of Hives who hired an outsider with no aircraft engine experience to see if a totally different perspective could improve the product and it did

Shortround6 · May 3, 2020

Part of Hookers claims to fame (there are several, not just the Merlin Supercharger/S) was getting the Bristol jet engines to work, working on the Pegasus vector thrust engine and after returning to RR, helping straighten out the RB 211

pbehn · May 3, 2020

Shortround6 said:
Part of Hookers claims to fame (there are several, not just the Merlin Supercharger/S) was getting the Bristol jet engines to work, working on the Pegasus vector thrust engine and after returning to RR, helping straighten out the RB 211

But that is ONLY 4 engines/power systems, not much really.

MiTasol · May 3, 2020

buffnut453 said:
Do you have something more definitive than hearsay on that story? I find it hard to believe that RR would take a component from a supplier, buy the rights to it and then produce it on their own. That doesn't make financial or logistical sense when you could just buy the component from the supplier. I can search online auction houses and find Delco-stamped starters for use on RR vehicles so, clearly, at some time RR just ordered direct from Delco.
Please provide evidence of this story.
And here we are

In the early 1960's Rolls Royce bought the manufacturing rights to the Continental 0-200 light aircraft engine. The RR adverts claimed RR had made some 200 improvements.
Very soon after the Airworthiness Directives (ADs), started to appear, and most, maybe all, required the replacement of a RR part with the original TCM part.
And at least one of those ADs applied to the starter. I read the ADs as they came out but never worked on a RR 0-200 so never needed to fully comprehend them. RR production only lasted a few years, probably due to the ADs

Shortround6 · May 3, 2020

MIflyer said:
The pistons in each RR built Merlin were hand selected during assembly in order have them near the same weight.

actually "The pistons in each ~~RR built~~ Merlin were hand selected during assembly in order have them near the same weight."

This is no matter who built them and/or overhauled examples.

From "Aircraft Handbook" by Fred H. Colvin on page 89 of the book.

"The Permissible variation in weight for any one assembled pair of rods, pistons, pins, and rings, in an engine, is 1 oz."

Permissible weight variation for the pistons selected for one engine was 1/2 oz.

This is from a 37 page chapter on overhauling a Merlin Series II engine with a number of new and allowable used tolerances.

To get that kind of matched weight is going to call for a bit of trial and error and/or a bit of material removal from the heaviest piston/s.
But to go from that to "hand fitted" is a different story.

If Packard or Ford of England was NOT building to those standards there were some serious issues as that kind of weight matching was NOT optional. It was part of the design specification and calculations for vibration and stress.

Now if somebody can come up with a RR specification that calls for an even tighter tolerance then we can conclude that the RR built engines were different. But we need numbers on a chart, form, blueprint, a set of assembly instructions, Not just story that RR built higher quality.

12 pistons of the size and weight of Merlin pistons matched to 1/2 an ounce from lightest to heaviest is a pretty fine tolerance.

fastmongrel · May 3, 2020

If all pistons were matched for weight by the worker how were they matched. Your going to need hundreds of pistons to choose from and a very accurate set of scales for each worker. To assemble one engine how many pistons do you have to go through to find 12 that match and how lucky would you need to be for the first 12 you picked up to match. Instead of the hundreds of Merlins per day that British factories churned out the RAF would be lucky if they got one a day.

pbehn · May 3, 2020

Shortround6 said:
12 pistons of the size and weight of Merlin pistons matched to 1/2 an ounce from lightest to heaviest is a pretty fine tolerance.

Not only weight, Merlins and all engines of the type burn oil because there is a clearance between piston and bore. To maintain the correct clearance between piston and bore across the production need extremely tight control on maximum and minimum size for both because the compression rings need a clearance to maintain compression and scraper rings need another clearance to work. It isn't easy, it needs a lot of work to get right, the people making these engines weren't fools neither at RR or Alisson. I frequently see anecdotes saying that P-51 pilots could tell a Rolls Engine from a Packard, how many P-51s were fitted with Rolls Royce engines?

An interesting read about the Packard built Merlin engine.

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