Category Archives: R975

Post # 68 The Chieftain’s Hatch does the M4A1, we review it.

Post # 68 The Chieftain’s Hatch does the M4A1, we review it: A great Hatch!

The video comes in two parts.

The subject of the video is  Black Magic, a small hatch, late production M4A1 if the turret came on it, though the turret or gun mount could be from other tanks. When it comes to restored Sherman tanks, I think being concerned about matching numbers is not a thing that seems to be worried about, and since it was so well designed and built, parts readily interchange. This sherman started life as a canadian Grizzly, basically totally the same as an M4A1 with an extra small hatch in the hull floor.

This tank has almost all the quick fix upgrades, the extra armor over the hull ammo boxes but lacks the cheek armor on the turret, and the turret may, I can’t tell for sure, have the cast in cheek armor, meaning it almost for sure didn’t come on the hull.  It also lacks the armor plates added in front of the driver and co drivers positions, that the Chieftain calls “sheet metal”.  It also has some late Sherman stuff, either added by the restorers, or by a depot rebuild later in the tanks life. The spot light, and ‘gun crutch’, or travel lock as normal people use were not on most small hatch shermans. Also the all around vision cupola would not be found on these tanks during WWII.

The Tom Jentz tangent. 

The Idea that the Sherman was no more reliable than any other tank, well, I don’t buy it. I like Mr Jentz’s work, and to some degree, his books helped inspire this site, since there was so little info on the web with really detailed info on the Sherman other than the Sherman Minutia site. I don’t think he really knows much about the Sherman if he thinks tanks like Panther and Tiger just needed more spare parts to be as reliable as the Sherman, it is a ridiculous idea. I do not think there was a single part on the Sherman that had a 500 kilometer life span, and that’s double the Panthers final drives.

First: The Chieftain himself has done Hatch posts on reports from the British, about how much more reliable, the M4A4 Sherman was than the Cromwell, even when both had full crews working to keep them running. both tanks were run thousands of miles, something late war German tanks could not do.

Second: In one of his own Hatches talks about the French experience with the mighty panther showed they averaged 150 kilometers per final drive set! Much less if the crew was hard on them.  There was no major automotive component including the oil, that had to be changed every 150 kilometers on any model of Sherman.

Third: This will focus on the Panther, since it was a major part of Germany’s late war armored force, and how terrible it was. This tank didn’t have just one flaw that should have disqualified it for production it had at least five. It was generally poorly reliable across all its automotive components, along with the final drive, 2500 kilometers for the motor and 1500 for the tranny were hugely optimistic and most of these tanks broke down and or were destroyed before they had to refuel. You had to take the whole drivers and co drivers compartment apart and the top of the hull off to change a transmission! Don’t get me started on the weak turret drive system that Rube Goldberg would have loved.  The  ‘wonderful’ dual torsion bar suspension and interleaved road wheels would cause any maintenance nazi to find the nearest US Line and surrender instead of working on it!

. . .

Another thing to note, you can see the holes drilled vertically in the suspension bogies, these are the tops of the holes the bolts that hold the suspension caps on go into. They were covered up with body filler by the factory, but on most restored and old Shermans the filler is gone, and they don’t fill the holes.

Note: the odd groove in the center of the rear Hull casting, this wasn’t done on all M4A1 tanks, and may have been unique to General Steel castings.

On the problems with the R975, I have not heard of complaints about the engine being easy to blow, and would be very surprised if the throttle wasn’t governed to prevent it.  On having to crank the engine before starting, I have it on good authority, that the crew could just start the tank and run it for a few minutes every 45 minutes to an hour to avoid having to hand crank the motor.

Many of units removed the sand shields in ETO to prevent problems with mud.

The Commanders vane site is an early version bolted to a late war vane site pad. The tank has the early style gunner’s periscope.  The gunners periscope is missing the linkage going down to the gun.  The radio looks like a 528.  Note the Armored doors on all the ammo boxes and ready rack. The tank is missing a lot of interior storage, it may have been removed in preparation on shipping the tank out to it’s new owners.

I‘m no expert, but I think the Chieftain confused a .30 cal ammo bin for the 75mm ammo bin right next to his shoulder for the location of an SCR-506, I just can’t see a WWII radio fitting in the tiny box! You can see how sparsely filled the interior is, as issued the tank would be stuffed full of items to help fight it, live with it, or keep it running.  The Chieftain shows just how easy even a small hatch Sherman was to get out of,  the the Loader was still going to have some issues though.  I wish he would have tried the belly hatch out, but maybe it’s welded shut or something.

He covers the small floor hatch on the Grizzly tanks, and you get a nice shot of the early escape hatch.  They also show the generator mounted on the rear of the transmission in one of the shots, briefly.  You can also see the full turret basket’s mesh screening that separated the turret crew from the hull crew. Part of the quick fix was to cut this all out.  I suspect most of the inconsistencies in the tanks details are due to the restoration crew using the Sherman parts they could get their hands on.  Very few people would  even notice or know it had the wrong commanders hatch, or even whole turret.

A note on the tank, it belonged to a the Military Vehicle Technology Foundation, a fancy name for the collection of a man named Jacques Littlefield. He had a passion for armored vehicles of all types but really liked tanks. He restored many to full functionality, including working main guns and machine guns on some tanks.  Owning a working tank cannon is easier than you would think, and far easier than getting the paperwork approved to own machine guns in California, and Jacques Littlefield did both.  He employed a restoration crew with world class skills and did some amazing restorations, including a Panther A that was impossibly damaged, but still brought back to life.  That Panther was his crowning achievement, and he was a real mover and shaker in the international military vehicle restoration scene, seeing that tank run was one of the last things he achieved, because cancer claimed him shortly after.

The MVTF was supposed to make sure the collection of vehicles, that were a labor of love his whole life, lived on when he passed. Unfortunately the location of the MVTF, Portola California, on a large chunk of very private property, with very limited parking really presented some problem.  The collection was used often while it was there, by TV productions like Myth Busters, and was a staple for the Wargaming Staff for their productions, and occasionally opened up to groups of vets, or other interested people.  There were other difficulties with the location, and ultimately the collection was donated to the Collings Foundation.  They reportedly decided to keep 40 of the most significant vehicles and auction the rest off.  The money from the auction was going to be used to build a facility in Stowe Massachusetts, but due to zoning issues, the permits were not provided, leaving the vehicles they did keep in limbo.

I‘m sure the Collings Foundation, a really amazing Charity, they keep many rare WWII aircraft, and cars, including race cars running, has a plan for the rest of the tanks. Their website only lists the Panther in their collection, I hope that doesn’t mean they sold the rest when the museum fell through.  That’s not a criticism of the CF, they I’m sure know their business far better than I do, and they really are a top notch group of people. Just browse that site to see the airplanes they’ve gotten flying.  The only real B-24 liberator and a working F-4 Phantom are just two of the notable planes!!  If you know anything about aviation, you know just how complicated and expensive keeping an aircraft like a Phantom flying is, especially if you don’t have the resources of the U.S. Navy or Air Force backing you.

I have to say, this is one of the best Chieftain’s hatches they have done. Granted, I’m a tad biased, since it was on the Sherman, well a Grizzly made into a later model small hatch Sherman anyway, and the Chieftain really has gotten pretty good with the Sherman and its sub variants, and even has a book on US WWII TDs on the way.




#16 The Sherman’s Motors: Four Motors Made It Into Production.

The Sherman Motors: Why So Many, And Why The Weird Ones?

The Sherman had four different motors that made it into production tanks. The R975 radial, The GM 6046 ‘twin’ diesel, the A57 multibank, and the Ford GAA V8.  There was also a Caterpillar motor they were playing I cover in the Shermans of the Future section.

There are several reasons the US went with the radial aircraft engine instead of a dedicated tank power plant, and this was mostly due to lack if money to develop tanks and their drivetrains between wars. When the US got serious about tank motors, there were a limited number of choices and the R975 was the best one. Then they turned to the US auto industry for other motor ideas, but only after war was clearly looming.

GM came up with their twin bus motor, the 6046 and it was well liked right from the beginning. Then Chrysler came out with the nutty but fantastic A57. The US Army didn’t like either, and didn’t want to even use them for training. If the British hadn’t been willing take the A57 versions, the Army would have regulated them to training use only. It wouldn’t be until Ford figured out the bugs in the GAA V8 that the US Army would make the switch from the R975. R975 powered M4s and M4A1s would serve with the US Army until the end of the war in just about every unit that used Shermans though, and they would not be phased out until after the war.

Post war many A4 tanks would have R975s put in them, or in much rarer cases, the 6046.  Parts for the A57 became rare post war, and people who knew how to keep them working were probably rarer. I’m pretty sure almost all A4s used post the 50s were converted to one or the other of these motors. Conversions to the Ford GAA were not done as far as I can tell, I think because the US Army was stingy with this model and spares for it, so they could keep for their own use or close allies.

The Continental R975 C1/C4: The Motor the Sherman was designed around
R975 without the fan and other accessories. Courtesy of the Sherman Minutia site.

The Continental R975 C1/C4:
Type: 9 cylinder, 4 cycle, radial
Cooling system: Air       Ignition: Magneto
Displacement: 973 ci    Bore and stroke: 5×5.5 inches Compression Ratio: 5.7:1
Net Horsepower:C1/C4 350/400 hp           Gross Horsepower: C1/C4 400/460 hp
Net Torque: C1/C4 800/ft-lb/940/ft-lb       Gross Torque: C1/C4 890ft-lb/1025ft-lb
Weight: 1137 lbs dry    Fuel: 80 Octane gasoline     Engine Oil Capacity: 36 quarts

This motor was a license built version of the Wright R-975 built by Continental for tank use. It had been around nearly ten years and used in civil aviation before the army started putting it in tanks, starting with the M2 medium in 1939 and would go on to produce more R-975s than Wright ever would, 53,000 motors total. The military version put out more horsepower than the civil version as well.  This was a solid and reliable tank motor, but not ideal. It was a little underpowered, and had to be revved up a lot to get the tank moving. The Army considered this a superior choice over the 6046 diesel and A57 motors, probably because it required a lot less maintenance than the other two motor choices.  This motor would be swapped into M4A4 hulls by the French post war, the French would use the A4, and A2 with the original motors during the war.

Another reason the motor was not idea was the shape, the R975 is wide and tall, and this dictated how large the rear hull of the tank had to be.  The only motor larger was the A57, and it was huge. There are still a lot of Shermans still running with this motor, either in civilian collections, or museums that keep running tanks.

The General Motors 6046: The Motor GM Came Up With To Power The Sherman
GM 6046 diesel, note the 6-71 roots type super charger. Image courtesy of Sherman minutia site.

The General Motors 6046:
Type: 12 cylinder, 2 cycle, twin in-line diesel
Cooling system: Liquid Ignition: compression
Displacement: 850 ci     Bore and stroke: 4.25×5 inches Compression Ratio: 16:1
Net Horsepower: 375    Gross Horsepower: 410
Net Torque: 1000 ft-lbs Gross Torque: 885-lb
Weight: 5110 lbs. dry     Fuel: 40 cetane diesel oil    Engine Oil Capacity: 28 quarts

First used in the M3A3 and M3A5 and then in the M4A2. This motor tied two GM super charged truck diesels together on a common crank case. The motors could be run independently, so if one was damaged the other could be used to get the tank back to a repair depot, or to keep fighting. The engine weighed more than the R975, but had better torque characteristics, and the tanks with this motor handled low speed operation better because of the superior torque.

M4A2 6046 motorKeyfor M4A2 pic

This version was ruled out for use by the Army because they didn’t want to complicate the tank supply chain by adding another fuel to it. This motor was well liked by its users, and the only version of the Sherman the Soviet Union would take via lend lease were the ones powered by this motor.  The Army testing of this motor found it was as reliable as or more so than the R975.

M4A2 6046 underside

This motor would run and drive the tank if one of the diesels failed. It has also been reported the Russians would use the ability to only run half the motor to sneak the tanks closer to German lines without being heard. They were impressed with how quiet the Shermans tracks were.

The early draw backs to this motor were tied to its air cleaner system for the motors; they would clog quickly and required a lot of maintenance. Getting the two clutches for the motors synchronized was difficult on early tanks with these motors as well and this made for short clutch life.  There were some other teething troubles with the fuel injectors and other problems, but these would all be solved early in the M4A2 productions, including improved injectors, air cleaners, and clutch system.

The US Army hadn’t wanted to use tanks with this motor in combat, but they ended up doing so, since this motor also powered the M10.

 The Chrysler A57 Multibank: The Motor Chrysler Came Up With To Power Tanks, It Was Crazy, And It Worked!


The Chrysler A57 multibank:
Type: 30 cylinder, 4 cycle, multibank
Cooling system: Liquid Ignition: Battery
Displacement: 1253 ci   Bore and stroke: 4.37×4.5 inches Compression Ratio: 6.2:1
Net Horsepower: 370    Gross Horsepower: 425
Net Torque: 1020 ft-lbs   Gross Torque: 1060 ft-lbs
Weight: 5400 lbs. dry      Fuel: 80 octane gasoline     Engine Oil Capacity: 32 quarts

This motor was a bit of an orphan in US Service. It powered the M3A4 and M4A4. The Army used the motor for training, and tried to pawn a few off on the Marines. That lasted about two months at the Marine Tank School. The ever growing need for tanks by the British ultimately solved what to do with the tanks that ended up with this motor. They would end up taking nearly 8000 of them. Chrysler sent tech reps to England with these tanks and showed the maintenance crews how to keep them running.  This worked well and the engines served their purpose with little trouble. Often powering the best pure AT version of the Sherman, the Sherman VC firefly.  This motor saw a lot of use, during the war, and after with many countries being given Firefly Shermans to help out their recovering militaries. Some even ended up in South America, but I’m not sure what versions. This is my favorite Sherman motor because it’s so absurdly complicated, it’s almost German, but it actually worked, so not German at all.

M4A4 labeled image front A57one water pump

This motor was fairly robust, and would continue to run and allow the tank to move with three of the five cylinder banks not working. This would make the tank severely underpowered, but would be useful to get it back to the repair yard or onto a dragon wagon. I’m sure it was much more common to have one of the five not operating right, and that level of power loss would be an annoyance, but wouldn’t keep the tank from fighting if it was really needed.

a57 top multipump

m4a4 a57 throttle linkage
The A57 Carb Linkage

During the war Chrysler really went to bat to keep these motors working well. Since it was based off a motor already long in production, spare parts were readily available. I’m not sure how long support for the motor lasted after the war. I doubt it was very long, and American car parts were probably not easy to acquire to keep these motors running. Because of this, the M4A4, more than any other model seems to have its engine replaced in post war service.  I’ve read about the twin diesel and the R975 being swapped in.  There are a few M4A4s around in Europe with running A57 motors, both fireflies if I recall right.  You have to love anyone willing to keep one of these motors running.

a57 single pump right side a57 right side multiopump

Daily maintenance could be done with the motor in the tank, carburetor and timing adjustments, fluids and filters and things like that. If anything major needed to be fixed, one of the motors had a bad piston or valve, or even something minor like a big vacuum leak on the intake of one of the motors, or even a leak in the cooling system, the whole motor would have to be pulled. Chrysler knew this, and made getting the motor in and out as easy as possible, including huge lifting eyes built on the common block to help lift the motor out.  The British probably had several depots setup to rebuild A57 power packs that were in need of major work, and Chrysler made a lot of spare motors and parts to support the motor.

a57side single waterpump A57 side view multipump

To be fair, many serious problems with the other tank motors would require pulling the motor to fix them as well.

The Ford Motor Company GAA V8: The Best Sherman Motor


The Ford GAA:
Type: 8 cylinders, 4 cycle, 60 degree V8
Cooling system: Liquid           Ignition: Magneto
Displacement: 1100 ci              Bore and stroke: 5.4 x 6 inches Compression Ratio: 7.5:1
Net Horsepower: 450 Gross Horsepower: 500
Net Torque: 950 ft-lbs               Gross Torque: 1040 ft-lbs
Weight: 1560 lbs. dry                Fuel: 80 octane gasoline Engine Oil Capacity: 32 quarts

The Ford GAA only made it into one Lee as a test bed. But it powered a lot of Shermans, both large and small hatch. It would go on to be the motor of choice for the US Army for the rest of the war, and in the next tank, the M26. Just look at the numbers above and compare them to the rest of the motors. The GAA is really a much better motor for a tank in the Shermans weight range. This tank was not lend leased to the other allies in large numbers if at all. The USSR may have gotten one to evaluate, the UK too, but the Army wanted to switch over to this and stop using R975 powered tanks. After the war, the only Shermans they kept were M4A3 76 w tanks, and over time they converted as many of these to HVSS suspension as possible. They went as far as swapping T23 turrets from M4A1 76 W tanks onto M4A3 75 hulls. The army would produce several other gas powered tank engines, but none would really shine like this one did in the Sherman.

The motor started life as a V12 Ford had designed to compete with the Rolls Royce Merlin, after a deal to produce the RR engine fell through. Ford was incensed that a deal could not be worked out and decided build his own V12 aircraft motor. When he tried to sell it to the Army he was turned down, but later when the army needed tank motors he used the V12 as a basis for the V8, by removing 4 cylinders. As a tank motor, it was under very low stress putting out only 500 horsepower, and could have been really upped in horsepower with a few tweaks.

This motor does not get much credit for how advanced it was. The much talked about, and unreliable as hell,  German Maybach HL 230 P30, the motor used to power the Tigers, and Panther tanks, was not nearly as advanced, or as reliable as this amazing V8. This V8 is apparently the largest gas powered all aluminum V8 ever produced. It has some very advance features, even for a modern V8, like a one piece cast aluminum block with dual overhead cams and four valves per cylinder a true, dual, overhead, cam, motor or DOHC. It had a very innovative 8 way power drive system for its accessories, like the generators, fuel and water pumps, and two magnetos. The motor used no belts or chains, everything was gear and shaft driven.

M4A3 firewall diagram engine in place m4a3 engine compartment rear

This motor saw post war use in civilian hands, from powering logging equipment, to use a stationary pump motors. The most interesting post war use is in pro tractor pulling and hotrod use. These installations in most cases just update the intake and exhaust using modern carbs, but in one crazy case down in Brazil they have updated a GAA with coil and spark plug and crank sensor` computerized ignition, fuel injection and twin turbos, and just 8 pounds of boost it makes 1500 hp, with a higher boost number the engine is capable of 3000 HP. For more info on these modifications and some pics, check out this link.   

GAA Data Sheet

Ford GAA V8 Data Sheet

gaa ignition wiring diagram GAA throttle linkage

Sources:  Sherman by Hunnicutt,The Sherman Minutia Site, Son of a Sherman by Stansell and Laughlin, M4 Sherman tank at war by Green, Tanks are a Might Fine Thing by Stout, , TM9-731B M4A2, TM9-731G M10A1, TM9-745 GMC M36B2, TM9-748 GMC M36B1, TM9-750M3, TM9-752 M4A3, TM9-754 M4A4, TM9-759 M4A3, TM9-1725 R975 C4, TM9-1731B Ford motors(GAA, GAF, GAN), TM9-1750F A57 Multibank