Can you rebuild a R-R Merlin in your garage?

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AI says the following (all the usual caveats about accuracy):

A vintage Rolls-Royce Merlin V12 engine typically costs between $20,000 and $60,000 for a non-running core, and $200,000 to over $500,000 for a fully overhauled, airworthy engine.

Then there's this info (Source: Bot Verification ):

Auctioneers Bonham's sold one for £20,700 in 2009 and Sotheby's sold one for £44,000 ($57,000) in 2019.

Bottom line is it's a really rich man's hobby. Location is probably a factor, too. I'd expect parts availability to be good in the UK, with options for (relatively) cheaper usable but non-airworthy spares. Parts will be harder to obtain elsewhere, with the possible exception of the US which has a lot of airworthy P-51s but scale of logistics to get parts remains something of a challenge.
 
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SaparotRob said:
Parts $carcity? Even basic stuff like rings, filters, gaskets must be difficult to source. BUT it has been done. There might be a network for sourcing the basic stuff for a rebuild.
As to costs, all heavier than air vehicles require heavier amounts of money.
Click to expand...

So, we can get down to the hard facts. Firstly, there is a big difference between a flight standard engine/build and the various levels of static or running ground engines. The flight standard we can define as built to the Rolls-Royce specifications, and here you are in the realms of hundreds of thousand £/$. However, for a ground running rebuild, the cost of parts is much lower. Nonetheless, Merlins do not grow on trees these days and like most historic things, they do have worth.
To start with, you will need a suitable garage/workshop. It needs to be at least double car size with power, lighting and some workbenches. A lathe and pillar drill are helpfull, but if you have to outsource welding / machining work you need to factor that.
You need at least a static engine stand, preferably a rotating stand, an overhead hoist and lifting gear. Later, the engine will need a display stand and a trailer in fact, a testing/running trailer for ground running. At the very start, you will need to have or hire the means to move your 1500lb weight engine to your workshop, without damaging it.
Comprehensive quality tools and equipment are required. Special tools and adapters are required for some jobs, often you need to fabricate adapters to properly lift or hold units or engine assemblies during strip or rebuild.
Now, the amount of work that an engine needs for ground running standard varies from the almost impossible to no work required! Most of us will have experienced buying a used car or vehicle, they vary from clapped-out trash to almost new condition. Used aero engines are the same. This is a really difficult part of the project. Unless you are able to see an engine running or buy it with genuine guarantees, it is very tricky. Chances are, your used Merlin for £10,000 is going to be a crusty non-running mess, if you are lucky it will be in a stand!
Here, I am afraid, you are on your own. If you watch Peter Grieve's rebuild of his crashed MerlinXX, you will see that it has amazingly little damage or corrossion. This is quite amazing.
Generally, used and long unmaintained engines have many problems, waiting for you to discover! Part of the problem is that these engines are very difficult to dismantle if they will not turn. There are ways and means for most problems but, as you can expect, the time and costs to sort problems can be prohibitive!

That is just a few of my thoughts. The whole thing is a bit like a very big vintage car rebuild, a bit like a large R-R or a Packard V-12!

What do you think?

Eng
 
re
Could a shop capable of rebuilding a sports car and/or associated engine rebuild a Merlin?

IMO it would depend on the extent of the rebuild necessary.

As mentioned above by SaparotRob and buffnut453, replacement parts would be a problem. If all it needs (more or less) is spare parts replacement and some minor rework that can be done in house or easily farmed out - then probably yes. Although, there would also be the need for special tools to be purchased and/or made - looking at the tool lists in the back of the Merlin engine repair manuals there are at least a couple of dozen that you cannot locate in today's tool catalogs.

But if the engine needs to have its cylinders rebored, new sleeves made, and maybe some of the crankshaft bearing/bushing seats returned and/or reground - then probably no.

One of the recurring problems I ran into during my career in manufacturing was the customer thinking that a 72" (or some such) long item could be machined in the normal machine shops - even the ones that you might find doing the rebuilds of car engines - and that the cost would be roughly the same based on simple proportions of the part. Such parts earn the name "oversize parts" due to being too large in size for 95-98% of machine shops. I worked for 32 manufacturing companies over the years, and aside from the Chrysler Tank Plant in Lima, and Gopher Machine & Engineering, none of them could handle things the size of a Merlin engine block or crankshaft.

Costs tend to go up depending on the size of the equivalent cubic footage of the part. If we assume an equivalent number of features being machined to the same/similar tolerance, and if a part of about 12"L x 12"W x 6"H cost $200, then a part at 12"L x 12"W x 12"H would cost about $500, and a part 36"L x 12"W x 6"H would cost about $1000, and a part 36"L x 12"W x 12"H would cost about $2000. The increase in height is usually a more difficult requirement to fulfill than an increase in length or width - at least to a certain size. Most non-specialty prototype and/or short-run machine shops had manual or CNC (Computer Numerical Control) machine tools that could handle parts - at a maximum - about 30"-36" in length, about 16"-20" maximum in width, and about 12"-14" in height. In today's world, something like 98% machined parts are less than 1" in diameter and/or width and less than 6" in length. Going to a part the size of a Merlin engine block/crank case (approximately 72"L x 24"W x 24"H) would require machines of significantly larger capacity than are commonly used, and said machines would have a disproportionate increase in price due to their uncommon size - which in return would increase the cost of the part.

Moving the part and performing the 'set-up' (placing the part in position and getting the machine ready to do the work) also takes a disproportionate amount of time relative to the size increase. Leaving aside the Chrysler Tank Plant - where they were oriented toward large parts and the machines and handling equipment were set up for such oversize work - at Gopher Machine & Engineering the largest parts I worked with were some cast blanks that started out at 3 tons and some forgings that started out at about 2 tons. IIRC, just positioning the blanks (using overhead cranes and such to move them into the correct position/orientation) and then securing them in place, took upto 4 hours all by itself. A similarly shaped 'normal' sized part that can be easily positioned by hand might take anywhere from 2 to 15 minutes.

The required cutting tools (drills, end mills/face mills, boring heads/bars, taps, etc) also cost significantly more for oversize features being machined into the oversize parts (for example a Ø5,4" x about 10" deep hole in a head vs a Ø1" x 2" deep hole in a smaller part), which also increases the cost out of proportion to the increase in size.

Inspection and quality control of oversize parts requires some sort of oversize inspection tools and arrangements - again increasing the costs. Even the oversize measurement & inspection tools like micrometers, digital or vernier calipers, bore gauges, depth gauges, etc, cost disproportionately more. Many smaller shops have a CMM (Coordinate Measuring Machine) that can handle parts of the smaller sizes I mention above, but a CMM capable of being used on a Merlin engine block would cost in the region of a million dollars when new.

Also, although it does not address the question directly, the need to be able to cover the potential expense of a screw up needs to be taken into account (no pun intended). How many shops could eat the cost of destroying an existing Merlin engine block or crank shaft, or even afford the cost of scrapping a new made Merlin engine block. This potential cost would normally be figured into the contract with the customer, but it is still tricky.

bleh
 
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There are a few points about Merlin parts. Certainly, the correct flight standard parts are very expensive. However, for a ground running restoration, used parts that don't meet the OE specs are commonly used. The Merlin has the close brother the Meteor tank engine, and that can provide many parts.
Cylinder liners are mentioned and these were only one size for the Merlin. Here, being slightly worn OOT is not a problem, the same for piston rings or pistons. Overall, the rpm and boost used on a ground running engine should be limited to match the standard of the build.
For ground running, major components are not going to be remade, but used parts are often traded.
Filters are no problem as most Merlins only have the scavenge screens, some Packards also have a self cleaning Cueno pressure full-flow filter, all these filters are cleanable.
Gaskets, there are not that many and most are available/remade. Tricky rubber seals and metal gaskets may need genuine parts or remade.
Plain Main bearings and Big-ends are quite large. Some may be re-metaled if required. Roller and Ball bearings are mostly specials and may need genuine replacements if required.

Cheers

Eng
 
Engineman said:
So, we can get down to the hard facts. Firstly, there is a big difference between a flight standard engine/build and the various levels of static or running ground engines. The flight standard we can define as built to the Rolls-Royce specifications, and here you are in the realms of hundreds of thousand £/$. However, for a ground running rebuild, the cost of parts is much lower. Nonetheless, Merlins do not grow on trees these days and like most historic things, they do have worth.
To start with, you will need a suitable garage/workshop. It needs to be at least double car size with power, lighting and some workbenches. A lathe and pillar drill are helpfull, but if you have to outsource welding / machining work you need to factor that.
You need at least a static engine stand, preferably a rotating stand, an overhead hoist and lifting gear. Later, the engine will need a display stand and a trailer in fact, a testing/running trailer for ground running. At the very start, you will need to have or hire the means to move your 1500lb weight engine to your workshop, without damaging it.
Comprehensive quality tools and equipment are required. Special tools and adapters are required for some jobs, often you need to fabricate adapters to properly lift or hold units or engine assemblies during strip or rebuild.
Now, the amount of work that an engine needs for ground running standard varies from the almost impossible to no work required! Most of us will have experienced buying a used car or vehicle, they vary from clapped-out trash to almost new condition. Used aero engines are the same. This is a really difficult part of the project. Unless you are able to see an engine running or buy it with genuine guarantees, it is very tricky. Chances are, your used Merlin for £10,000 is going to be a crusty non-running mess, if you are lucky it will be in a stand!
Here, I am afraid, you are on your own. If you watch Peter Grieve's rebuild of his crashed MerlinXX, you will see that it has amazingly little damage or corrossion. This is quite amazing.
Generally, used and long unmaintained engines have many problems, waiting for you to discover! Part of the problem is that these engines are very difficult to dismantle if they will not turn. There are ways and means for most problems but, as you can expect, the time and costs to sort problems can be prohibitive!

That is just a few of my thoughts. The whole thing is a bit like a very big vintage car rebuild, a bit like a large R-R or a Packard V-12!

What do you think?

Eng
Click to expand...
Informative plus insightful equals winner.
I think this project is beyond me. I failed miserably trying to build a Stipa-Caproni from a toilet paper tube.
 
Hi everyone.

I do hope that some of you might now consider obtaining a historic aero engine! For those that have just bought a used Merlin, you are probably asking, "Great, but where is the Haynes overhaul manual"?
Yes, even with Pete's great video's, you really need some help with the detail.
I will describe my view of where the details can be found. This is not the entire detail of what is out there, just my understanding!
Firstly, we must understand that Rolls-Royce were a commercial engine maker and originally supported their products with manuals, according to the requirements and payment of their customers.
So, starting at the beginning, Rolls-Royce designed and built their engines with factory documentation for all aspects of construction, operation, maintenance and overhaul. In the pre and post WW2 years, these R-R documents included Civilian versions for operation, maintenance and overhaul of the specific engine types. Generally, the maintenance documents do not include the full technical overhaul of the crankshaft / rods / bearings or the salvage (repair) of many parts. The depth of detail on full engineering is in very specific documentation.
Rolls-Royce sold the very technical detail on a strictly limited basis.
The Military engines were generally supported with the R-R documentation but, for example, the RAF re-wrote or reproduced the information in their own format(s). Therefore, you will find mixtures of R-R manuals and RAF AP's (Air Publications) that are similar, but different!
During and after the WW2, there were large civilian and military overhaul factories and it is likely that they had similar but different R-R and RAF manuals.
Of course, Packard followed in similar ways, and all major military operators had their own versions!
You can still find many of these publications but, it can be difficult to track down a full set for your particular engine!
IMO, the full factory overhaul tech detail is the most difficult to find, probably because there were far fewer full overhaul works, whereas, every Squadron needed the basic operating and maintenance documents.
Apart from stating that it is best to have the exact correct manuals for your specific engine, it is worth noting that R-R themselves combined the civilian maintenance manuals for single-stage Merlins after WW2 into one series. For the 2-stage engines Merlin 60 to Merlin 85 there is the RAF AP 1590 P,S and U. Full overhaul information needs the other unknown (by me) documents, although I am sure they are available, at a price.

I hope that helps a bit! Just going back to my spanners!

Eng
 
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