1939–1953 International Harvester Farmall A, AV, B, BN & International A Tractors / U-2 Power Unit Service Manual (P/N 57722 D)

This International Harvester service manual covers the 1939–1953 Farmall A, AV, B, BN, International A tractors, and U-2 Power Unit, with engine and chassis repair information and model-specific service references.

• Engine repair: Cylinder-head and valve service, piston and sleeve replacement, connecting-rod inspection, crankshaft bearings, camshaft removal, and timing-gear alignment.

• Fuel system and governor: Zenith and Marvel-Schebler carburetor disassembly, inspection, and reassembly; jet identification; governor synchronization and speed-control troubleshooting.

• Ignition and electrical: H-4 magneto installation and timing, generator-output diagnosis, starting-motor checks, battery testing, and ignition and charging-system wiring diagrams.

• Cooling and lubrication: Thermosiphon cooling, radiator and fan service, gear-type oil-pump inspection, pressure-regulator checks, and oil-filter identification.

• Clutch and transmission: Tractor and power-unit clutch adjustments, transmission and differential disassembly and assembly, and bevel-gear contact-pattern checks.

• Brakes and chassis: External contracting brake adjustment and relining, differential- and axle-shaft removal, steering-gear disassembly, and front-wheel alignment.

• Attachments: Belt pulley and power take-off construction, bearing and seal arrangements, and attachment-selection tables for different transmission cases.

Originally prepared exclusively for International Harvester dealers, this manual is intended for dealer workshop service and repair.

Engine, Cooling, and Lubrication Service

The wet-sleeve engine sections distinguish matched piston-and-sleeve assemblies from replaceable precision connecting-rod and crankshaft bearings. Sectional and exploded views accompany clearance specifications, connecting-rod alignment checks, and valve-train service.

The bearing discussion explains how dirt behind a bearing shell can distort it, causing localized overheating and bearing failure.

Cooling coverage includes capacity data and identifies two fan-hub assemblies whose individual parts are not interchangeable. Lubrication coverage includes oil-pump gear-clearance inspection and the pressure-regulating valve; oil-filter selection distinguishes engine Nos. 501–97937 from 97938 and up.

Zenith and Marvel-Schebler Carburetors

Separate service procedures cover Zenith Model 161 and Marvel-Schebler TSX carburetors. Jet-identification tables distinguish tractor and U-2 applications for gasoline, kerosene, and distillate, helping match replacement jets to the carburetor identification disc.

The carburetor cautions explain how cleaning with wire or drills can damage calibrated jet openings. Governor coverage adds spring and weight identification, linkage synchronization, and checks for hunting, supported by an exploded view and a schematic of the throttle-control mechanism.

Magneto, Generator, and Starter Diagnosis

The ignition wiring chart accompanies magneto installation and timing instructions. Complete H-4 magneto overhaul is referred to the separate CHS-27 manual, which is not included.

Generator and starting-motor checks address the cutout relay, electrical connections, brushes, commutators, and Bendix drive. Generator and electric starter-and-lights wiring diagrams show the related circuits.

Ignition and electrical work requires precautions against accidental starting and battery short circuits.

Clutches, Bevel Gears, and Chassis

The tractor spring-loaded dry clutch and U-2 overcenter clutch have separate adjustment guidance. Complete clutch rebuilding is referred to the separate CHS-62 manual, which is not included.

Transmission and differential service explains shaft removal, shim placement, pitch-line intersection, and tooth-contact patterns for bevel-gear alignment. Brake-relining instructions distinguish the access arrangements on A/AV/International A tractors from those on B/BN models.

Steering-gear cross sections show the different worm-shaft and bearing layouts. Final-drive, rear-axle, belt-pulley, and PTO sections describe bearing and seal installation and early versus later attachment arrangements.

Reference material includes transmission speed charts, U-2 standard net power and part-throttle fuel-consumption curves, and model-specific dimensional drawings. There are 80 numbered illustrations plus three service charts.

A Preview of Cylinder-Head and Bevel-Gear Specifications

These engine and drivetrain values are a small selection of the repair specifications in the manual.

For the shared tractor and U-2 engine, the cylinder-head section specifies 65 ft-lb for the head-stud nuts and 0.0015 to 0.0035 inch of valve-stem-to-guide clearance.

For the tractor differential, bevel-gear-to-pinion backlash is 0.005 to 0.007 inch, measured at the closest point of bevel-gear runout.

PDF Navigation, Diagram Detail, and Page Count

Text search and wiring detail: Text search is unavailable for the manual content, and there are no embedded PDF bookmarks. Small terminal labels in the wiring diagrams are readable with magnification.

The download is one printable, English-language 71-page PDF. The total includes 64 numbered manual pages, three inserted service-chart pages, one cover page, one general-specifications page, and two additional nontechnical pages.