Bad Steel in the Rolls-Royce Merlin?

[Koopernic]

Note that the original 100 octane that the RAF used to replace 87 octane really was only 100 octane ie more like 100/100 and purchased or "free" lend lease supplied from American refineries. It did not have as significant rich mixture response. The latter 100/130 came from the addition of synthetic alkylate produced from acid alkylation. Hence the RAF can thank Major Jimmie Doolittle for winning the BoB because it was he who apart from BeeGee racing, and heading the Tokyo air raid from the Aircraft carrier Hornet was responsible for aviation fuels development at shell in the 1930s and make sure there was refinery capacity to produce 100 octane. The process of catalytic cracking with regenerative catalysts was used. The rich mixture techniques developed and tested in Schneider floatplane trophy racing must have come into use well after BoB.

Without the 100 octane fuel Merlin power was around 1030 rather than 1280.

The Germans struggled as their investment was directed at coal to oil technology. They used a different way of producing octane from syngas to upgrade their fuel but latter also added alkylation.

 

[GregP]

It cannot be like you said Shortround. If all Rolls Royce did was sort through bins of parts, they would have had a huge mountain of scrap parts that didn't exist. And they didn't have that when Merlin production ended. Not all their parts fit other required parts, and they DID had fit and had file. They just tried to start with a part closer to what was needed to reduce the hand-fitting process. That's why they call it hand fitting. If the production process produced parts as loose as you contend, then they HAD no process.

Can't buy it, but there is NOTHING wrong with a hand-fitted Merlin ... until you needs spares and don't have the skills available to re-fit new parts. Then you sell it to someone who has the expertise and go get a Packard, so you can get parts that work without all the hand fitting. You STILL have to hand-lap the main, rod, and cam bearings, but not hand-fit EVERYTHING. If you can't do that, you can't fly a big V-12 airplane from WWII that experiences wear unless and until you find someone who CAN do it.

I can tell you from personal experience that main bearings for Allisons and Merlins do NOT fit today when brand new (because ALL are remanufactured ... no NEW mains for a LOT of years), or the manufacturing process is just plain old wrong. They remanufacture the bearings oversize so they require hand-lapping, plastigage, and go-no go gauges for fitting crankshafts fitted with plain bearings of any kind. To get away from that, you need to go to ball-bearing mains. Neither the Merlin nor the Allison have ball bearing mains.

On page 135 of the Rolls Royce Merlin Service Manual for Series II engines (1938), the clearance for the main bearings is .004 - .00475. for new bearings (hand lapped) and .006 when it reaches the service limit. If you try to run it with larger clearances, you lose too much oil pressure and it falls out of flight limits. Other version have similar clearances.

Same for an Allison, but the actual clearance may be slightly different. Haven't checked in a couple of years ... I seem to recall .003 - .005.

The actual spec calls for installing a crankshaft gauge tool and tightening the main studs to full torque. You MUST be able to rotate the tool by hand (yes, there IS a torque spec). Trial and error for some years sets the actual clearances that you must scrape to, and they are covered in a separate maintenance instruction so that if the manual falls into enemy hands, they can't assemble it successfully without a complete set of manuals. No single manual had ALL the specs. The guys who do Allisons HAVE all the specs today a,d share them among themselves.

 

[pbehn]

It cannot be like you said Shortround. If all Rolls Royce did was sort through bins of parts, they would have had a huge mountain of scrap parts that didn't exist. And they didn't have that when Merlin production ended. Not all their parts fit other required parts, and they DID had fit and had file. They just tried to start with a part closer to what was needed to reduce the hand-fitting process. That's why they call it hand fitting. If the production process produced parts as loose as you contend, then they HAD no process.
.

I don't believe they had bins full of parts as in finished parts but blanks or part machined pieces awaiting the final cut. In the early days RR needed to make Merlins for themselves to get an engine that worked and could be tested. Then they needed engines for prototype Spitfires Hurricanes Defiants and Battles. The early orders for these aircraft were in hundreds not thousands and you do not set up or use mass production techniques for small production runs.

 

[Shortround6]

Note that the original 100 octane that the RAF used to replace 87 octane really was only 100 octane ie more like 100/100 and purchased or "free" lend lease supplied from American refineries. It did not have as significant rich mixture response. The latter 100/130 came from the addition of synthetic alkylate produced from acid alkylation. Hence the RAF can thank Major Jimmie Doolittle for winning the BoB because it was he who apart from BeeGee racing, and heading the Tokyo air raid from the Aircraft carrier Hornet was responsible for aviation fuels development at shell in the 1930s and make sure there was refinery capacity to produce 100 octane. The process of catalytic cracking with regenerative catalysts was used. The rich mixture techniques developed and tested in Schneider floatplane trophy racing must have come into use well after BoB.

Without the 100 octane fuel Merlin power was around 1030 rather than 1280.

The Germans struggled as their investment was directed at coal to oil technology. They used a different way of producing octane from syngas to upgrade their fuel but latter also added alkylation.

You are in error about the British 100 octane fuel. It did have a rich mixture response. We have been over this many times. The British were NOT saved by American 100 octane fuel.
American 100 octane fuel could NOT have more than 2% aromatic compounds.
British 100 octane fuel could NOT have less than 20% aromatic compounds.

This was included in the list of specifications for the fuels by the respective governments/buying agents. The British may have bought fuel from "American" refineries but it was to their specification and not American specification. The British also had refinery/s in the Americas, such as the one/s in Trinidad that reached a capacity of 285,000 bbl/day in 1940. There were also refineries in England capable of making 100 octane fuel from imported feed stocks.

British 100 octane fuel during the Battle of Britain did vary from batch to batch but was usually between 115 to 120 for rich response when tested later after the invention/development of the Performance Number Scale.

American 100 octane was just about 100PN for rich mixture response although it to could vary a few points up or down from 100. A few batches were 100 octane lean and in high 90s running rich.

The Schneider floatplane trophy racers in the last of the 1920s and in the 30s didn't even run on gasoline but some rather exotic fuel blends cooked up by Francis Rodwell Banks. Try googling him before you give ALL the credit for 100 octane fuel to Major Jimmie Doolittle.

BTW the British knew about rich mixture response even with their 87 octane fuel, they just didn't know how to specify it in numbers directly. They did know that fuels with a fair amount of aromatic compounds did have better rich mixture response than fuels with little or no content of aromatics.

 

[Shortround6]

It cannot be like you said Shortround. If all Rolls Royce did was sort through bins of parts, they would have had a huge mountain of scrap parts that didn't exist. And they didn't have that when Merlin production ended. Not all their parts fit other required parts, and they DID had fit and had file. They just tried to start with a part closer to what was needed to reduce the hand-fitting process. That's why they call it hand fitting. If the production process produced parts as loose as you contend, then they HAD no process.

Bearings may in a different catagory than pistons.

There are maximum and minimum dimensions, as you well know, and if a part is over or under it won't even get to the assembly area.

According to one book I have the Merlin pistons were supposed be between 5.370 and 5.368 in measured at the top at right angles to the gudgeon pin when new and 5.380 to 5.378 at the bottom of the skirt also at a right angle to the gudgeon pin. A 0.010 taper? allowance for greater expansion in the piston head when hot? Clearance between Piston and cylinder wall was 0.030 to 0.034in at the top and 0.020 to 0.024 at the bottom when new. Permissible worn was 0.045 at the top and 0.035 at the bottom.

A fitter/assembler might very well measure a cylinder bore and select a piston that gave a good fit, it might be the first he picks up up. It might not be a good fit for that cylinder but might very well fit the 2nd or 4th cylinder better.

Things like pistons and piston-rod assemblies also had weight tolerances. I don't know what the minimum and maximum weights were but all the pistons in a single engine had to be within a 1/2 ounce range (including rings) which means it was quite possible to assemble an engine using all light pistons, another using all medium pistons and a 3rd using all heavy pistons and yet meet the specification.

Clearance of the crankshaft bearings was 0.004 to 0.00475 new and 0.006 maximum worn. Crankshafts were allowed to be reground twice.

I would note that many cars of the time used poured babbit bearings that needed to be scraped and lapped to fit.

Unless someone can actually find descriptions of workers measuring up a cylinder bore and then measuring a piston out of a rack of pistons, taking said piston over to a lathe. putting said piston into a chuck or fixture and then taking a "cut" of a few thousands of an inch and going back the engine to fit the piston to the piston rod and then repeating this process over and over I think we can dispense with "filing and fitting".
There may have been a bit of filing, grinding or drilling to remove a bit of weight to bring an over weight piston into spec but I would imagine that this would be done before the pistons got the assembly area. Having metal chips or metal filings floating around your final assembly area isn't a very smart thing to be doing.

 

[GregP]

Right, you don't usually file or hone pistons. That's why they have rings!

Perhaps I simply misunderstood and your intention is correct. It's happened before, Shortround, and I VERY rarely catch you wrong. Probably fewer times than your wife does ...

Just to be clear, there is NOTHING wrong with hand-built craftmanship. It runs great, last as long or longer than mass-production engines, and has only the shortcoming that fitting replacement parts may be troublesome compared with the mass-produced engine. To many, that is not a problem.

Also, the British engines said "Rolls Royce" on them, and that has been worth something. quality-wise, for a LONG time. No argument there ...

 

[fastmongrel]

purchased or "free" lend lease supplied from American refineries.

Have a look at when the Lend Lease was signed and when it came into effect.

As for 100 Octane most used by the RAF in 1940 came from refineries in the Caribbean, Venezuela and the Persian Gulf. Any that came from US refineries was paid for Cash and Carry no credit allowed. Theoretically if the Germans had the cash they could have bought fuel from the US.

 

[Shortround6]

I would note that there was a short lived American specification for 100/125 fuel.

The Americans and British agreed to a "common" 100/130 fuel specification shortly after that.
However they went through at least 3 different specifications for 100/130 fuel that differed in the amount of allowable lead per gallon and perhaps other things. There may have been either later specifications or combined changes for allowable amounts of certain aromatic compounds along with the last change in allowable lead. I don't know, most accounts are not clear. However each change allowed for increase production of 100/130 from the available base stocks (more gallons of aviation fuel from the same number of tons of crude).
I do know that post war there was one specification for military 100/130 fuel and another for civilian or commercial 100/130 fuel. The Commercial/Civilian fuel was allowed less lead per gallon. More expensive (needed more costly base stock) but saved on spark plugs and plug changes.

The History of aviation fuel is not well documented and has to be drawn from various places.

Roy Fedden of Bristol was another Englishman who pushed for 100 octane fuel during the late 30s. His company had nothing to do with fuel except wanting the greater performance such fuel would bring.
Rolls-Royce had announced power levels for the Merlin at the 1938 Paris AIr show/exhibition using "100" octane fuel but I don't know if the 100 octane they were testing in 1938 was the same as the British government was buying and stockpiling in the fall of 1939.

 

[pbehn]

I would note that there was a short lived American specification for 100/125 fuel.

The Americans and British agreed to a "common" 100/130 fuel specification shortly after that.
However they went through at least 3 different specifications for 100/130 fuel that differed in the amount of allowable lead per gallon and perhaps other things. There may have been either later specifications or combined changes for allowable amounts of certain aromatic compounds along with the last change in allowable lead. I don't know, most accounts are not clear. However each change allowed for increase production of 100/130 from the available base stocks (more gallons of aviation fuel from the same number of tons of crude).
I do know that post war there was one specification for military 100/130 fuel and another for civilian or commercial 100/130 fuel. The Commercial/Civilian fuel was allowed less lead per gallon. More expensive (needed more costly base stock) but saved on spark plugs and plug changes.

The History of aviation fuel is not well documented and has to be drawn from various places.

Roy Fedden of Bristol was another Englishman who pushed for 100 octane fuel during the late 30s. His company had nothing to do with fuel except wanting the greater performance such fuel would bring.
Rolls-Royce had announced power levels for the Merlin at the 1938 Paris AIr show/exhibition using "100" octane fuel but I don't know if the 100 octane they were testing in 1938 was the same as the British government was buying and stockpiling in the fall of 1939.

Great post SR and you have made many on the same subject. Why not just put all that you know in a post/thread over a period of time so that such discussions can be answered with a link to it. Each post is informative but just forms a patchwork spread all over forum discussions which are impossible to find. This thread is about bad steel in Merlins, it wouldn't show up readily in a search about fuel.

 

[wuzak]

Note that the original 100 octane that the RAF used to replace 87 octane really was only 100 octane ie more like 100/100 and purchased or "free" lend lease supplied from American refineries. It did not have as significant rich mixture response. The latter 100/130 came from the addition of synthetic alkylate produced from acid alkylation. Hence the RAF can thank Major Jimmie Doolittle for winning the BoB because it was he who apart from BeeGee racing, and heading the Tokyo air raid from the Aircraft carrier Hornet was responsible for aviation fuels development at shell in the 1930s and make sure there was refinery capacity to produce 100 octane. The process of catalytic cracking with regenerative catalysts was used. The rich mixture techniques developed and tested in Schneider floatplane trophy racing must have come into use well after BoB.

BeeGee Racing

 

[buffnut453]

I could have gone my ENTIRE LIFE without seeing that photo. Thanks a bunch. Now it's burned into my memory. My eyes!!! MY EYES!!!!!

 

[ChrisMcD]

It cannot be like you said Shortround. If all Rolls Royce did was sort through bins of parts, they would have had a huge mountain of scrap parts that didn't exist.

Not sure what the quantity was, but a lot of Merlin parts that failed quality control were used in the Meteor tank engine - as were '"crashed" merlins that were not considered airworthy
Rolls-Royce Meteor - Wikipedia

 

[ChrisMcD]

On the subject of 100 octane for the BoB, this link is interesting

100-Octane

AFAIK the two opinions are mostly correct and together give a fairly complete picture.

I have a feeling that once a lot of American engines were in Britain in 1941, there was a move to co-ordinate Octane numbers. Probably after the problems with P-38's.

 

[tomo pauk]

On the subject of 100 octane for the BoB, this link is interesting

100-Octane

AFAIK the two opinions are mostly correct and together give a fairly complete picture.

I have a feeling that once a lot of American engines were in Britain in 1941, there was a move to co-ordinate Octane numbers. Probably after the problems with P-38's.

Thanks for the link.
'Problems' with P-38 were related to many things, fuel not being high on the list, if even it was on the list.
By the time P-38J was in problems (winter of 1943/44), the Allies have long accepted the 100/130 fuel as standard.

 

[swampyankee]

Selective fit is anathema to the assembly line, but as recently as thirty or so years ago, it was normal practice for production of civilian firearms. Firearms need close fits and the extra labor costs of selective fit were lower than the costs of machinery that could hold tight enough tolerances.

 

[Shortround6]

As I have mentioned before my father was a production engineer for Colt firearms from the early 60s to the early 80s.
The parent company, Colt Industries, used profits from the M-16 during the Vietnam war to by up other companies, like Holly Carburetor and Fairbanks Morse pumps rather than invest in new tooling.
While they may not have been using machine tools dating back to Sam Colt himself some of the machine tools were pretty old and not in the best shape. Like drill presses that tended to "wander" and hand fitting was still the order of the day on revolvers. Some parts were "stoned" into tolerance on the assembly benches as they were already heat treated and filing wasn't going to work. My father did get a blueprint changed for a cylinder stop (the part the fits into the notches at the rear of the cylinder) like this one.

After he found that the assemblers were having to stone .005-007in of the top of the lug to left on average to get them to fit. Management agreed to change the dimensions so they only had to stone off .002-004in
CNC machines were just coming into service an I can remember a few times my father went to trade shows and came back with demonstration samples from machines.
One reason Colt had such high prices at the time was that they had a truly horrendous scrap rate and high manufacturing costs but the "Colt" name they could charge the higher prices and get away with it. Very few bad parts made it into finished guns but an awful lot of semi-finished parts went out the door in scrap barrels. But no new machines was the order of the day from management.

 

[ChrisMcD]

Thanks for the link.
'Problems' with P-38 were related to many things, fuel not being high on the list, if even it was on the list.
By the time P-38J was in problems (winter of 1943/44), the Allies have long accepted the 100/130 fuel as standard.

Not my area of expertise, and no way am I sticking my finger into that mincer! But this thread seems to have considered it important.
The P-38J and L in the European theater.

 

[Aozora]

One of the best sources of information on the developmental and production problems of the Merlin is The Merlin in Perspective:The Combat Years, by Alec Harvey-Bailey (Rolls-Royce Heritage Trust, Historical Series No 2) Amazon product ASIN 1872922066View: https://www.amazon.com/Merlin-Perspective-Combat-Years-Historical/dp/1872922066

Harvey-Bailey became head of quality control for Merlin production: some excerpts from his book are attached. Most of the steels and alloys used in the Merlin were developed by Rolls-Royce specifically for high powered aero-engines, so the claim that there was "poor quality" steel used is completely wrong: as Harvey-Bailey explained, the biggest problems encountered in the Merlin came about through some poorly designed components that were redesigned as soon as any weaknesses were discovered.
Also attached is an interesting article by A.C Lovesey, one of the main engineers in charge of Merlin development: Cyril Lovesey - Wikipedia This article is posted on WW II Aircraft performance http://www.wwiiaircraftperformance.org/merlin-lovesey.pdf

 

[fastmongrel]

One of the best sources of information on the developmental and production problems of the Merlin is The Merlin in Perspective:The Combat Years, by Alec Harvey-Bailey (Rolls-Royce Heritage Trust, Historical Series No 2)
View: https://www.amazon.com/Merlin-Perspective-Combat-Years-Historical/dp/1872922066

Curse you. Thats another book I will have to buy and add to the groaning bookcase.

 

[Shortround6]

It does spell out most if not all of the differences between the different Merlins although a bit short on actual time lines.

Some experimental versions are in the tables.