Merlin Versus Allison Overhaul Time

[Aozora]

I don't believe you could work on an Allison without some of the special tools Joe Yancey has made. The "dumbed down" socket sets you can buy today certainly won't do it. Some of the special tools are made using a standard socket of appropriate size and a 1/2" or smaller end mill on a rotary table. I'm thinking of the cam tower wrenches that are necessary but oh so scarce, and a few other "specials" such as the towers needed to pull the cylinder banks off and split the cases. There is a bizarre tool needed to change the cylinder bank studs and you also need a torch to heat the Aluminum case while you tighten or loosen the slightly oversize studs.

The set of specials is large for the Allison ... but nothing like the specials needed for the Merlin. My Merlin friends have entire tool cabinets just for the "specials." They might let you LOOK at one, but forget borrowing it. You have to go make your own.

Here's a list of some of the tools required for the V-1710

Plus more general comment regarding the six major sub-assemblies of the Allison, and an "Engine Dismantling Chart":

 

[GregP]

Thanks for the Allison list.

The "Main Bearing Removal Tool" cracks me up. I use a piece of 2 x 4 wood. Works great and cannot damage anything because it is softer than anything you push on with it. But I'd like to see one anyway. Maybe it IS a piece of wood! The trick is getting the bearings out without dropping them on the floor.

We had 2 or 3 "camshaft housing packing nut wrenchs" but also made our own on an end mill equipped with a rotary table. Ours seem to work better than the originals do, but having an original is a good thing if you work on Allisons. Finding one can be problematic but, if I ever SEE one, at least I'll know what it is and can pick it up.

Since whoever has it probably never sold one before and might not know what it is, maybe it will be cheap ...

It is vital to have the various stands or the subassemblies are hell to work on.

 

[DerAdlerIstGelandet]

You also KNOW which combination of extensions are needed on a ratchet drive for which bolts/nuts and you may have acquired a few "cheaters". My Father worked for Sikorsky and Chance Vought for several years in WW II and his tool box in the 1950s still had a few wrenches that were cut off short and a few that were little more than the end of wrench with a long rod welded to the side in order to get into certain confined areas. Anybody doing a LOT of overhauls might acquire a few "extra" tools over and above what the manual calls for that save time or skin on the knuckles

Aint that the truth. I have several self made and modified tools. Just cut up a 16mm socket on Monday to make an elevator trim tab actuator rod removal tool. All so that I did not have to pull the elevator back off.

Over time you modify and make special tools to get the job done.

 

[Gixxerman]

I suspect the Daimler Benz engines were in line with the Allisons at around 200 hours or so for an average overhaul, but I have no data to back that up with.

I've just got hold of the very good 'One Summer, two Messerschmitts' video from Planes TV.
I highly recommend it - great photography, interesting interviews and they made 2 audio tracks, one without much commentary or music...just the music of that deep V 12.

The guys on that talk about the DB605's (they're both DB605's, one is the pretty well known 'Black 6' G-2 and the other is 'Black 2' - wiki says it's 'Black 12'? - a converted Spanish Hispano HA-1112-M1L converted to the DB engine) having 150hrs between major servicing...but with the caveat that, as with all historic aircraft something could break at 30hrs, 50hrs or tomorrow.

 

[Airframes]

Accounts from former Luftwaffe pilots and ground crew, normally mention the DB engine in the '109E needed to be changed at 100 hours, with the removed engine going for total rebuild. Certainly many period photos from 1940 show engine changes in the field, with stacks of crated DB engines in the background.

 

[Glider]

Any mechanic with time under his belt will have a compartment in his tool cabinet full of odd special tools he has made over the years. One day you will be looking at a seized woggle grommet shaft and think "aha I have the very left handed screwdriver I need". I have special tools I probably made 40 years ago when I was an apprentice I cant remember what they were for and they are probably for cars, motorbikes, lifts, cranes, railway locomotives and wagons that barely exist these days but you never know one day maybe one day.

Happens today in IT projects as well. I was doing a Satellite Latency project a number of years ago and obviously we needed to test it on a satellite. This was going to cost a fortune so we needed a specific satellite simulator to try it on first and these were not at the time the most common bits of kit. This was fine until the project using it before us had issues and our delivery date was at serious risk. I got everyone together to explain the problem and one of the techies took me on one side and told me he had one in his garage. Problem solved and after that I always wanted him on my projects. I don't know how big his garage was but he always seemed to have something when we needed it.

 

[Aozora]

Any mechanic with time under his belt will have a compartment in his tool cabinet full of odd special tools he has made over the years. One day you will be looking at a seized woggle grommet shaft and think "aha I have the very left handed screwdriver I need". I have special tools I probably made 40 years ago when I was an apprentice I cant remember what they were for and they are probably for cars, motorbikes, lifts, cranes, railway locomotives and wagons that barely exist these days but you never know one day maybe one day.

My great uncle told me that when he was a trainee mechanic for the RNZAF he was once told by the sergeant in charge to find a Left-handed grub-screw and digit extractor # D1-G1T; when he couldn't find one the sergeant said "Well gee, if you can't extract your ****** digit what the **** makes you think you're ever going to be a mechanic?"

 

[GregP]

I heard in another forum that the DB's were "serviced" at 100 - 150 hours, but that didn't come across to me as "overhaul" at the time.

Again, I stress that if the Germans did "major service" at 150 hours, it doesn't mean that was the engine's life. It means they wanted to freshen up the engines at that interval. The Allisons and Merlins were not flown untli they were worn out, they flew until the prescribed time was reach and then were overhauled regarless of status.

Many time the Germans were operating from farmer's fields as a forward landing strip and I'd bet they injested a lot of dust and debris. I've seen film clips of 109's taking off from dirt fields, and it wasn't exactly the best conditions from which to operate an aircraft. Engines in severe climates, even in today's cars with efficient air cleaners, require service more often than engines operated in a clean environment.

I'd bet some money that the DB's were as durable as any engine, but suffered from the operating environment.

I wonder how long the Merlins used in Malta lasted with coral dust in the air all the time?

 

[rinkol]

The German's had a different philosophy for engine overhauls. Their later engines were designed to be quickly removable for rework in specialized facilities. This might have been partly a result of the complexity of the fuel injection and engine control systems. Also, I can imagine that an inverted V12 would not be the easiest engine to service when installed in an aircraft.

 

[vikingBerserker]

My dad ( a car nut) had a great saying that IMHO is applicable here. "Anybody who designs an engine for a car should have to first work on them in the car."

 

[Milosh]

I wonder how long the Merlins used in Malta lasted with coral dust in the air all the time?

More like limestone dust Greg.

 

[GregP]

Methinks you are correct, Milosh.

I was thinking of coral atols in the Pacific and also remembering at the same time that the planes flown in Malta had VERY short engine life, even with tropical filters instaled. I never saw a figure for it, but have read in at least 3 - 4 places about short engine life flying from Malta.

 

[Aozora]

Methinks you are correct, Milosh.

I was think of coral atols in the Pacific and also remembering at the same time that the planes flown in Malta had VERY short engine life, even with tropical filters instaled. I never saw a figure for it, but have read in at least 3 - 4 places about short engine life flying from Malta.

The same thing happened in Normandy, this time with the Sabre engines; it was discovered than when the top soil was stripped away to lay down the airfields, the underlying soil the region is made up of about 80% of a hard, abrasive silicate which destroyed the sleeve valves and laid down a hard deposit on the spark plugs withing something like 6-8 hours. By then the Merlins on the 2 TAF Spitfires were equipped with decent filters.

 

[cherry blossom]

Henry Ford, who famously discovered that the kingpins in Model T engine never failed and so had them made to a lower spec, would say that the V-1710 and V-1650 were therefore over-engineered, and that the J47 which wears out when it reaches its designed lifespan is a better design.

Rather off topic but according to David Isby at Source for Luftwaffe Jagdwaffe joke? - Luftwaffe and Allied Air Forces Discussion Forum there was a Luftwaffe joke that "When an FW-190 crashes, they take the wreckage to Kurt Tank and he strengthens the parts that failed. When a Bf-109 crashes, they take the wreckage to Willi Messerschmitt and he lightens the parts that stayed together".