Technical Details of the Willys MB and Ford GPW

This section is mostly done.

Engine

The engine was a militarised version of the Willys-Overland "Go-Devil" motor used in the Americar civilian car. Chief Engineer Delmar G. Roos was hired by W-O in 1938 to improve the engine which at that time suffered from excessive oil usage, burned bearings, knocking, cylinder head leakage and generally poor performance. Roos boosted the horsepower from 45 to 60 by increasing RPM from 3600 to 4000. To do this the iron pistons were replaced with aluminium and the cooling system changed. After more redesigning the test engine would run at 4000 RPM for 100 hours without failure. The engine mounts were changed to allow it to be installed in the jeep. Carburetor changes for steep angles were made and the vacuum advance removed from the distributor.

	Fuel.........................Gasoline (petrol)
	Layout.......................L-head, side valve
	Material.....................Cast Iron block, head and manifolds
	Cylinders....................4
	Bore.........................3 1/8" (79mm)
	Stroke.......................4 3/8" (111mm)
	Piston Displacement..........134.2 cu in. (l)
	Compression Ratio............6.48 : 1
	Horsepower...................60 bhp @ 3600 RPM
	Compression..................111 psi @ 185 RPM
	Firing Order.................1-3-4-2
	Piston.......................Aluminium, 3 rings
	Connecting Rod...............9 3/16" (233mm) between centres
	Camshaft.....................Chain driven
	Carburetor...................Carter Model WO-539S downdraft
	Generator....................Auto-Lite GEG-5001A 6V 40A
	Starter Motor................Auto-Lite MZ-4113 185 RPM 70A no-load
	Voltage Regulator............Auto-Lite VRY-4203A 6V 40A

Running Gear

Gearbox: The transmission consists of a 3-speed T-84 syncromesh gearbox mated to a 2-speed transfer case. The gearbox has synchro on 2nd and 3rd gear. The leftmost Nomenclature Plate has the shifting pattern: Reverse at top left, First at bottom left, second at top right and third at bottom right with a neutral middle position. The casing has two drain and fill plugs on the left side. GPW housings have a script 'F' on the left side.
(Here are photos of a T-84 gearbox by Terry Howe)

	Make.........................Warner
	Model........................T84J
	Type.........................Synchromesh on 2nd and 3rd
	Mounting.....................bell housing and chassis crossmember
	Shift lever position.........centre top of transmission
	Speeds.......................3 forward, 1 reverse
	Ratios (1/2/3/r).............1:2.665, 1:1.564, 1:1, 1:3.554
	Oil..........................SAE 90 or equivalent
Transfer Case: The transfer case primarily consists of a main housing with three shafts: input shaft from gearbox, a central intermediate shaft and the double ended output shaft to the front and rear tailshaft universals. The output shaft has the selector fork gear arrangement, dog clutch and speedometer worm drive. External to the rear of the transfer case is the handbrake drum and contracting handbrake band assembly fixed behind the rear tailshaft universal.
	Make.........................Spicer
	Model........................18
	Mounting.....................rear of gearbox
	Shift levers.................high/low range, front axle engage/disengage
	Ratios.......................High 1:1, Low 1.97:1
	Oil..........................SAE 90 or equivalent

Chassis

The chassis is constructed of heavy 1/8" (3mm)(approx) stamped steel rails separated by three crossmembers in the GPW (four for the MB) not including the front and rear bumpers. The front crossmember supports the radiator, the middle crossmember supports the gearbox and the rear crossmember supports the optional floor pedestal for the machine gun. Unlike the postwar Land-Rover, the MB/GPW chassis was purposely designed to absorb some of the rugged shock by flexing in addition to the spring/shock absorbers. The Ford version has a completely boxed in region extending from the front crossmember to the pintle hook brace at the rear, with circular and elongated cutouts, whereas the MB does not. Technically the GPW chassis is mostly of better design, for example the inverted U front crossmember is riveted to the rails rather than the welded hollow tube. However, the MB shock absorber towers are of simpler and more durable construction.
	Frame........................SAE 1025
	Depth........................4.186" (106mm)
	Thickness....................0.083" min
	Length.......................122 3/4" (3118mm)
	Width front..................29 1/4" (743mm)
	Width rear...................29 1/4" (743mm)
	Wheel base...................80" (2032mm)
	Weight.......................140 lbs. (63kg)

Wheels

The jeep wheels are usually known as combat rims or split rims, because a tire can be changed in the field without requiring removal machinery. The damaged tire is deflated and the rims separated, a new tire and tube inserted and the rims reassembled. The wheel rims are of two piece construction with an inner main stamping and outer ring affixed with 8 bolts. Originally the rims had a "bead lock" ring between the halves to stop tube pinching, but if you find an unrestored rim this is usually so deteriorated that it can't be used, and modern tires will work just fine without it anyway. Reproduction rims are available, they are made in France for M201's and are expensive, but the ones I have seen look absolutely perfect copies.

	Make.........................Kelsey-Hayes 25692
	Diameter.....................16" (406mm)
	Width........................4 1/2" (114mm)
	Tire Size....................16 x 6" non-directional bar tread

Body

The body is basically the Willys MA pattern with Ford pressed grille. Prior to early-mid 1944 bodies were built seperately for Ford and Willys; after this they used the same "composite" body with Willys toolbox lids and Ford toeboard gussets. The body tub is fabricated from 18-gauge steel for the side panels and 16-gauge steel for the floor. Manufacture of the bodies was undertaken at various plants including the Lincoln car plant and the Budd Company. As far as I understand, composite bodies were also produced by American Central Manufacturing Corp.

Performance

Colour Schemes


Radio-equipped jeeps

This snippet from Gerry Davison on MIL-VEH some time ago, in answer to the question " Is it possible to obtain some information about the type of radio used in a radio-jeep in Normandy during WW2?":
According to Hayes Otoupalik (in Supply Line - January 1996) for the Willys use:
Apparently these sets are (or have been) available from Hayes Otoupalik, Fax (406) 543-0040

Australian radio jeeps
The Type 133 transmitter filled a whole Type 3 or 3A trailer. A good photo of a jeep and trailer from I Corps (Signals) appeared in John Edwards' 1997 WW2 jeep calendar.
I have an australian Type 22 backpack wireless set that is very similar to other radios used in jeeps. They were mounted on a small tray fixed to the top of the wheel arch. More information to come.


Terrific site which has exploded diagrams of all major MB/GPW components:
http://myweb.worldnet.fr/~souchman/jeep/Manuel/manuel.html

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Copyright © Steven Malikoff 1998; Last updated: 12-May-00