Allison v-1710 Engine Life

This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules

I`ve heard this many times, and I`m afraid I dont believe it, and I have never once seen any evidence for either figure (I`m sure the 7000 is true, but I dont think
any supercharged aero V12 will have a parts count varying by more than about 25% to any other, what on earth could they be ?, surely this is
something like one person counting each carburettor jet and magneto winding wire, and the other person ignoring all the ancillaries)

Even if each bolt had an extra lock pin and washer it would not amount to more than a few hundred bits.

Until someone takes both engines to bits and films it, and counts the bits - this one is firmly in the "myths" basket for me. I dont know, maybe if you
picked a fuel injected two-stage 1946 Merlin-100 and the very first V-1710 ever made in 1930... but like-for-like, no way.

As you will see in my book, generally speaking in terms of the basic engine architecture, I rate the V-1710 more modern than the Merlin.

View attachment 734853

Maybe you haven't looked at the nut, bolt, and screw count when the engines are all apart in front of you. Understandable. Most of us haven't. I have been lucky in that regard. I worked at an Allison shop for more than 3 years and have volunteered at a museum where they sometimes take Merlins apart right in the restoration hangar where I work on restoration. Having seen both in pieces, I believe it.

Rolls-Royce seems to have the philosophy, "why use 40 screws when 100 works so well?"

Here's a center shot of a Merlin from the front:
125-34.jpg

Note the number of screws and bolts.

Here's a center shot of an Allison from the back:
iveryService?id=NASM-NASM2022-00873-000001&max=900.jpg


BIG difference in parts count from the intake manifold system alone.

Not trying to be snarky here, Callum. Just observing and, in the case of Allisons, I spent most of my time disassembling them in the overhaul process. Some assembly. But mostly disassembly and cleaning the parts. It isn't straightforward to take an Allison or a Merlin apart to component pieces.

It takes 2 - 3 people about 13 weeks to overhaul an Allison V-1710. 12 weeks to disassemble, prep, replate, inspect and generally freshen up the parts and 2 - 3 days to assemble one, depending on interruptions. Takes another 3 - 4 days to put it on a test stand, pre-oil and run it in (seat the rings) until the inside of the exhaust manifolds turns light gray instead of dark wet black. Then you can ship it.

Cheers. Oh, and, I have your book. Magnificent work, Callum.

Sign me up for your book on radials when you write it.
 
Last edited:
Dam phone..
The F29 and F30 were rated for 1725 at 3200rpm. It wasn't used in service because the tip speed was too high on the propellers. This was a problem for many US aircraft. The P-47D with paddle blade propellers and the B-25 were both fast at lower rpm. Late war and post war manuals for the B-25 don't bother with listing mil power settings for this reason.
I the only B-25 manuals I can find that states this are" B-25 Pilot's Handbook for B-25J, TB-25J, and PBJ-1J, AN 01-60GE-1, 1-Apr-1947" and "Flight Operating Instructions - B-25J, AN01-60GE-1, April 25,1953"

On another note.
The V-1710F17R has 7413 parts and 925 part numbers
The V-1650-3 has 9764 and 1808 part numbers.
These figures include sub assemblies. This raises the totals a little more than what they should be.
I used the part catalogs "Parts Catalog - Allison V-1710-F, ALD-1F4D" and "Parts Catalog for V-1650-3, -7, -13, and Merlin 68 and 69 Aircraft Engines, AN 02A-55AC-4, 4-Mar-1949" to compile these.
 
BIG difference in parts count from the intake manifold system alone.
The Merlin appears more compact and looks like a much better overall design as far as fitting it into an aircraft, the Allison on the other hand has it's cam drive gearbox's? outside the profile of the engine and it's intake manifold looks convoluted with plenty of choke points.
 
I the only B-25 manuals I can find that states this are" B-25 Pilot's Handbook for B-25J, TB-25J, and PBJ-1J, AN 01-60GE-1, 1-Apr-1947" and "Flight Operating Instructions - B-25J, AN01-60GE-1, April 25,1953"

On another note.
The V-1710F17R has 7413 parts and 925 part numbers
The V-1650-3 has 9764 and 1808 part numbers.
These figures include sub assemblies. This raises the totals a little more than what they should be.
I used the part catalogs "Parts Catalog - Allison V-1710-F, ALD-1F4D" and "Parts Catalog for V-1650-3, -7, -13, and Merlin 68 and 69 Aircraft Engines, AN 02A-55AC-4, 4-Mar-1949" to compile these.
Nice work. The last total I heard for the Merlin was a bit over 11,500 parts. Was also compiled from the parts list, but was done by an engine overhauler. Can't say, myself since I have never done a parts count personally.

There IS a pretty big difference in regular service requirements. With a Merlin, you need to remove the valve covers and re-torque the valve seats and cylinders every 25 hours. You do not have to torque the valve seats in the Allison at all, and the cylinders only get torqued (to 2,200 ft-lb) when a cylinder bank gets installed. There is no re-torque requirement for the Allison.

But both start and run great ... and run for a long time quite smoothly and well, today or back in WWII.

The biggest issue with both Merlins and Allisons today is not getting run often enough. Neither one likes it when you let it sit for a long period (long enough for the oil film to drain away completely) and then start it without pre-oiling it for 30 minutes to 45 minutes or so.

The people who run them infrequently get short engine life. The people who run them frequently get long, relatively trouble-free engine life.
 
Last edited:
The Merlin appears more compact and looks like a much better overall design as far as fitting it into an aircraft, the Allison on the other hand has it's cam drive gearbox's? outside the profile of the engine and it's intake manifold looks convoluted with plenty of choke points.
The Allison intakes are equal-length units. The Merlin intakes aren't. So your observation there isn't quite inline with real life. The Merlin is not really much more compact in general. They are substantially the same size.

The dry weight of a V-1710-89/91 is 1,350 lb. Later Allison were closer to 1,450 lb. A Allison F-30R (which is a V-1710-111) will fit inside a box 29.3 in wide, 37.6 in tall, and 86 in long.

The dry weight of a Merlin 66 is 1,645 lb, but that is a 2-stage engine. A Merlin XX ws 1,420 lb. Much more comparable to the Allison in that regard. Later Merlins were 1650 lb. A Merlin XX fit inside a box 29.8 in wide, 41.2 in tall, and 70.6 in long.

It's a rare aircraft when 16 inches make a difference. The engine mounts are usually pushed farther forward than that for CG purposes. Radial engine mounts are sometimes several FEET longer for CG purposes. They had NO trouble converting from an Allison to a Merlin or even back again. The Allison would have to be moved forward anyway since it was generally a bit lighter than a Merlin.

So, the Allison and Merlin, both single stage, are almost exactly equal in width (within 1.7%), The Allison is 9% less tall than a Merlin, and 18% longer than a Merlin. One is an updraft carb and one has a downdraft carb. The Allison, if viewed from above looks busier because you can see the carb and distributors. The Merlin, if viewed from below, looks busier because you can see the same carb, etc. on the Merlin from below.

The Allison was a bit lighter, dry weight-wise. Later, the 2-stage Allison was maybe 80 lb heavier than the Merlin, likely due to the second stage being external to the engine. The wheelcase had some weight. Early to mid-war, the Merlin usually put out slightly more hp and had slightly better altitude performance. Once the 2-stage 60-series Merlins showed up, the hp increased slightly, but the altitude performance really jumped, versus the single-stage Allisons. Not so for the Turbosupercharged units in the P-38 or the later aux-stage Allisons. Late-war, they were well matched, hp and altitude-wise. The late Allison never got quite sorted because jets were higher on the priority list than pistons were. I have personally seen a G-series Allison putting out some 2,200 hp race at Reno without issues because the guy who built it, Joe Yancey, knows what he is doing with any piston engine. Of course, it also wasn't running at racing speeds at 30,000 feet, either. But it WAS running at racing speeds at Reno and won Bronze, won Silver, and then went back to the standard Allison for the Gold race because they weren't going to run faster than 430 mph or so in what was a 485 mph race anyway. A lot of the deficiency was that fact that the particular Yak-9 airframe in question wasn't optimized for speed like Strega and Voodoo were and are. That makes a difference that is difficult to quantize because of the large power difference between a stock P-51D and either Strega's or Voodoo's airframes. How much speed delta is due to power and how much to aerodynamics? I personally can't say, but I suspect the power difference is the main contributor to the speed difference. A stock P-51D makes 1,490 hp or so. Either Strega or Voodoo likely make close to 3,850 hp.

If you use the old cube root of the ratio of the power delta and use 1,490 hp and 360 mph (stock P-51D performance region) and 3,850 hp for the new power with no other changes, you get 494 mph for the new speeds, which is very close to reality. That's what makes me think it is mostly power than makes the difference.

So, anyway a sorted G-series unit is a known real possibility since it was DONE recently, and that didn't quite really happen during the war.

All for now. Cheers.
 
Last edited:
Depends on power ratings, which supercharger boost plays a huge role. Merlins late in the war (1945, such as the 100 series and V-1650-9) were rated for 80"/25 lbs dry WEP (no ADI) and 90" with ADI for the -9. Even the Merlin 60 series and -7 engines were ultimately rated late war for 80" WEP. I think the big difference between the 100 series and 60 series is that the rated power for the 100 was with 18 lbs/67" boost, which was like 15 lbs for the 60 series.

The Brits were running their Allisons in their Mustangs on operations to 70" boost in 1942 apparently without difficulty, and Rolls-Royce had Merlin 60 series engines making over 2000 hp at the same time on engine dynos.

There was also the aborted RM 17SM Merlin that made the following:

2,640hp was achieved with +36psi boost, >PN150 fuel and ADI, and at 3,150rpm.

2,380hp was achieved with +30psi boost, PN150 fuel, dry, and at 3,300rpm.

2,200hp was achieved with +30psi boost, PN150 fuel, dry and at 3,000rpm.

The 2640 was absolute max tested at. 2380hp may've been a WEP/combat rating if it entered production, It was rated for 2200 hp in MS gear and 2100 hp in FS gear.

The was also a V-1710 that on a dyno made almost 3000 hp, but this was a turbo compound engine (similar to a lot of the more powerful post war Wright R-3350 engines used in airliners and transport planes).

Of course, for the RM 17SM Merlin and the turbo compound Allison, jets took over. The P&W R-2800, R-4360 and Wright R-3350 (normal supercharged and turbo compound) did get a stay of execution because range limitations of jet engines making them not well suited for heavy transport aircraft or airliners until the DH Comet (which had its own non-engine related issues in early models).
 
Yeah, the ultra-high hp Merlins and Allisons never flew. They were wonder engines, but came when the high-hp piston engines were just not on the menu for the militaries of the world, which were, after all, the biggest customers for same before jets became all the rage.

That's why I was referencing engines that were actually used in production aircraft ... single and 2-stage units that were used during the war in mass-produced aircraft. Those will supply the best comparisons between the types rather than one-off test-stand mules.
 
That's why I bring up the Merlin 100 and Merlin 60/V-1650-7 engines. 81"/25 lbs boost wasn't a one off, given that RAF Mustang 3s (and even single stage Mosquitos) on V1 duty often ran that much boost.



http://www.wwiiaircraftperformance.org/150grade/Re-rating_V-1650-7_6sept44.jpg (not the most legible)


The best I've seen for war time use for the V-1710 was 70" for the P-38J/L (same as what the RAF did for their Allison Mustangs as early as 1942) and 75" for the XP-40Q.
 
That's why I bring up the Merlin 100 and Merlin 60/V-1650-7 engines. 81"/25 lbs boost wasn't a one off, given that RAF Mustang 3s (and even single stage Mosquitos) on V1 duty often ran that much boost.



http://www.wwiiaircraftperformance.org/150grade/Re-rating_V-1650-7_6sept44.jpg (not the most legible)


The best I've seen for war time use for the V-1710 was 70" for the P-38J/L (same as what the RAF did for their Allison Mustangs as early as 1942) and 75" for the XP-40Q.
70" and 75" are the best "official and approved" boosts I have seen for Allisons, too, despite Ben Kelsey recommending 75+" to the USAAC. The USAAC was nothing, if not conservative.

Unofficially, taken from conversations with former WWII vets who flew Allisons in combat, they sometimes ran them at whatever boost they could get and many times at higher than recommended rpm. That was well over 80" at times. The general consensus is that it didn't seem to hurt the engines. One guy who visited the Allison shop where I was working at the time allowed he had run the Allison in a P-40 at 3600 rpm and 86" and it didn't hurt the engine OR the propeller.

Of course, that is heresay. But he clearly recalled the numbers and the performance. This was in 2009 - 2010, and he started up the run stand Allison were were using like an old pro which, of course, he was. He predicted within 30 seconds when the temperature would hit "bottom of the green," and knew to change RPM very gradually during break-in. He had a very nice visit and signed our engine stand.

That was Maj. Gen John R. Allison (retired, unrelated to Allison engines). He had seven victories and several more probables, and commanded 75th Fighter Squadron and the 1st Air Commando Group. He passed in 2011. Nice fellow when he visited the shop and later was a VIP guest at the Planes of Fame Airshow in 2010 where the theme was "The Greatest Generation."
 
Last edited:

Users who are viewing this thread

Back