Farmall A/AV/B/BN & International A Tractors, U-2 Power Unit Service Manual (1939–1952)

This International Harvester dealer service manual covers Farmall A, AV, B, and BN tractors, the International A industrial tractor, and the U-2 power unit.

Bookmarks and Wiring Diagram Readability

Navigation and diagram detail: The PDF has 26 embedded bookmarks covering the major systems and dimensional drawings. Text search is not available for the manual content. Small wiring-diagram labels are readable when enlarged.

The English-language download is one printable 64-page PDF, including the printed index and model-specific dimensional drawings. It contains 80 numbered illustrations.

Engine, Fuel-System and Drivetrain Service

The overview highlights selected service topics, rather than the complete contents. Other sections explain air-cleaner maintenance and intake-manifold heat control.

• Engine repair: Cylinder-head and valve service, selectively fitted pistons and wet sleeves, connecting-rod alignment, crankshaft bearings, camshaft and timing gears, and oil-pump inspection.

• Carburetors and engine controls: Step-by-step Zenith Model 161 and Marvel Schebler TSX disassembly and reassembly, plus IH H-4 breaker service, ignition timing, and governor synchronization.

• Cooling system: Thermosiphon cooling, radiator and fan service, radiator shutters, heat indicators, and separate cooling notes for the No. 22 harvester-thresher engine.

• Clutch and drivetrain: Clutch inspection and adjustment, tractor transmission and differential disassembly and reassembly, bevel-gear setup, brake service, and final-drive and axle-shaft removal.

• Electrical diagnosis: Generator-output checks, cutout-relay and lighting-switch diagnosis, starter and Bendix-drive inspection, battery tests, and electrical wiring diagrams.

• Chassis and attachments: Steering-gear removal and sealing, front and rear wheel arrangements, tire and liquid-ballast information, attachment tables, and PTO conversion details.

Prepared expressly for IH dealers, this manual is best suited to experienced mechanics working from specification tables, sectional drawings, and concise factory procedures.

Engine Fits, Bearings and Lubrication

The engine sections cover valve-seat and guide work, piston-ring evaluation, sleeve removal and installation, and crankshaft seals. Specification blocks provide component-specific torque data, fits, wear limits, and spring tests.

Engine sectional views and an exploded view of the crankshaft, connecting rods, pistons, and sleeves support the internal repair information. The bearing sections address nonadjustable precision bearings and Tocco-hardened crankshaft journals, while the lubrication chapter explains pressure-oil passages and oil-pump inspection.

The fit and wear data support decisions about reusing worn components or replacing them. Oil-filter applications are separated by engine production range, with different replacement elements for the earlier and later filter arrangements.

The sleeve section warns against interchanging selectively fitted pistons or piston pins. It also identifies the ring-travel ridge as a source of damage to the piston or a new top compression ring.

Carburetors, Magneto and Governor

Separate Zenith 161 and Marvel Schebler TSX repair sections cover cleaning, inspection, calibrated-jet protection, float-level setting, and reassembly. Jet-identification tables distinguish tractor, U-2, and No. 22 applications for gasoline and kerosene/distillate use.

The engine descriptions distinguish gasoline, distillate, and kerosene configurations, with natural-gas equipment also discussed for the U-2.

Governor material covers spring and weight selection, speed adjustment, surge diagnosis, and governor-to-carburetor synchronization. The governor schematic and accompanying checks connect linkage wear, binding, and mixture faults with unstable engine speed, helping distinguish governor problems from carburetor-related causes.

H-4 coverage includes breaker-point service, magneto-to-engine timing, and firing-order wiring. Complete magneto overhaul requires the separately referenced Blue Ribbon Manual No. 1, Form CHS-27.

Cooling and Fan Assemblies

Cooling information distinguishes the regular thermosiphon arrangement from the pressure-cooled No. 22 harvester-thresher engine. Fan service notes explain that complete assemblies can interchange, while their individual parts cannot necessarily be mixed.

Clutch, Differential and PTO Work

The clutch sections distinguish the tractor’s foot-operated spring-loaded clutch, the U-2’s hand-operated overcenter arrangement, and the No. 22 harvester-thresher clutch. Complete clutch removal and rebuilding information is referred to separate Blue Ribbon Manual No. 10, Form CHS-62.

Tractor drivetrain procedures extend through shift-rail inspection, differential service, bevel-pinion positioning, tooth-contact assessment, and backlash adjustment. Brake-relining access differs by model and side of the tractor; final-drive material covers differential-shaft and axle-shaft removal and seal installation.

The PTO section distinguishes early nonstandard 1-1/8-inch equipment from the standardized 1-3/8-inch arrangement and identifies conversion package 66191-D. A belt-pulley/PTO cross-section shows the drive, bearings, seals, and shim locations.

U-2 transmission and reduction attachments are listed in the attachment table; the transmission overhaul procedures describe the tractor drivetrain.

The unnumbered center-of-book Service Charts referenced by the printed index are absent from this PDF.

Electrical Diagnosis and Chassis Reference

The generator and electric starter-and-lights wiring diagrams accompany checks of the charging circuit, cutout relay, light switch, wiring connections, starter, Bendix drive, and battery.

The electrical chapter warns that operating without a battery while leaving the generator field circuit closed can damage the generator windings.

Steering coverage distinguishes the B/BN universal-jointed worm-shaft arrangement from the one-piece shaft used on A, AV, and International A tractors. Frame and axle descriptions, wheel arrangements, tire applications, and liquid-ballast information accompany the dimensional drawings, including side, front, rear, and drawbar views.

The manual does not contain a hydraulic-system repair chapter.

A Preview of Valve, Ring and Bevel-Gear Clearances

Valve data specify 0.014-inch clearance between the valve lever and valve stem with the engine at operating temperature. Piston specifications give a ring end gap of 0.010–0.018 inch.

The bevel-drive setup section specifies 0.005–0.007-inch backlash, measured at the close point of bevel-gear runout. Tooth-contact illustrations show how the contact pattern relates to pinion position.

Caution: Heavy machinery maintenance carries inherent risks. Always verify procedures and consult a certified heavy equipment mechanic before beginning any teardown or overhaul.