Bolens 1978 Medium Tube Frame Tractor Service & Repair Manual (P/N 552875-1)

This May 1978 Bolens Medium Tube Frame Tractor Service & Repair Manual (Form Number 552875-1) covers the listed gear-drive and hydrostatic tractors, including the 600, 800, 1050, 1256, and 1656.

Printable PDF and Wiring Diagram Detail

Text search and wiring labels: Use the printed contents page to locate sections by their printed page numbers. The PDF has no searchable text or embedded bookmarks. Small wire-color and switch-terminal labels are best read at higher zoom.

The download contains one printable 100-page PDF in English. The total includes 99 manual pages, counting the cover and contents page, and one clutch-kit installation sheet, Form 1770402 (June 1994).

Ignition Diagnosis, Drivetrain Repair, and Lift Service

This selection of workshop topics shows the manual’s repair and diagnostic coverage. Other examples include optional lighting-kit wiring and starter-generator belt adjustment.

• Electrical diagnosis: Model-specific magneto, battery, and solid-state ignition diagrams, with ignition-switch continuity, solenoid, battery, and brake and PTO interlock tests.
• Gear-drive repair: Three- and six-speed transaxle assembly, controlled differentials, shaft installation, worm-wheel centering, and dedicated bearing and oil-seal tools.
• Hydrostatic service: Eaton Model 10 package removal and installation, seal and charge-pump service, hydrostatic transaxle assembly, and neutral adjustment by linkage design.
• Fuel and engine: Carburetor adjustments, fuel-system troubleshooting, air-cleaner service, engine fault charts, and engine removal and reinstallation.
• Chassis and PTO: Steering alignment, clutch friction-disc replacement, brake adjustments, belt guides, PTO shaft and seal service, and seat interlock switches.
• Hydraulic lift and maintenance: Lift-cylinder seal repair, pump and valve service, filter identification, maintenance schedules, and separate gear-drive and hydrostatic lubrication charts.

This manual is suited to mechanics familiar with transaxle assembly and electrical testing who have access to an arbor press and the specified service tools.

Ignition Variants and No-Crank Diagnosis

The G-10 (1055) has separate diagrams for Tecumseh solid-state ignition and Briggs & Stratton magneto ignition. The G-14 diagrams distinguish the circuit from serial 0400101 and the additional interlock from 0500101. Matching the diagram to the tractor helps identify the switch and interlock connections before tracing a no-crank fault.

An exploded view identifies the components of the Delco-Remy generator. The 1220 (193-01) diagram marks the ignition-switch connection where battery voltage can permanently damage the ignition unit.

Gear-Drive Assembly and Eaton Model 10 Repair

The gear diagrams show engagement by gear and range alongside exploded transaxle views. Assembly procedures cover worm-shaft end play and differential shimming, with Worm Centering Kit No. 171-9432 specified for six-speed worm-wheel alignment.

Model 10 service covers the control-shaft and input-shaft seals, reservoir adapters, auxiliary charge pump, and finned cover. The manual flags internal damage that can result from forcing the control arm off its shaft.

The neutral-adjustment procedure for the 1225, 1256-01/-02/-03, and 1257 differs from the procedure for the 1256-04 and later linkage. That distinction helps identify the right adjustment when a tractor creeps in neutral.

Clutch, Steering, and Brake Service

The clutch procedures cover friction-disc bonding and heat curing for six-speed and older three-speed assemblies. The included installation sheet distinguishes old- and new-style adhesives for clutch-facing kits 1770396, 1770397, and 1770401 and friction-disc kits 1770398, 1770399, and 1770400.

The chassis section shows how the steering pinion aligns with the front wheels and how the clutch and main brake work together. It distinguishes parking-pawl, disc-brake, and PTO brake arrangements. The maintenance charts include cooling air screens, drive belts, and transmission filters.

Before working on drivetrain components or starting the engine, review the manual’s safety precautions to prevent accidental engagement or injury.

Hydraulic Lift Circuits and Filters

Flow diagrams distinguish the self-contained optional lift kit from earlier and later systems powered by the hydrostatic charge pump. The later circuit shares its oil supply with the transaxle and hydrostatic transmission. The fault chart distinguishes hose leakage from internal seal leakage when a raised load drops with the valve in neutral.

The filter illustrations show where to find the spin-on and in-line filters, including the sump-cooled H-14 and H-16 systems from serial 0200101.

Fuel-System Service and Engine Coverage

The fuel-flow diagram accompanies fault charts for hard starting, fuel starvation, and rough running. Carburetor guidance identifies fixed high-speed jets on some Tecumseh HH-160 and most HH-140 engines. Air-cleaner service distinguishes paper, oil-foam, and oil-bath designs.

Engine tables cover Briggs & Stratton, Wisconsin, and Tecumseh engines, including the HH-100, with bore and stroke, oil capacities, and ignition data. Engine procedures cover troubleshooting, removal, and reinstallation. Internal engine overhaul is outside the manual’s scope.

The PDF contains Groups I–VII. Group VIII, Service Letters and Bulletins, appears only in the printed contents.

Battery Load Test and Axle End Play Examples

The starter-battery load test specifies a minimum of 9.0 volts at the end of 15 seconds of cranking. The battery should be approximately 80°F and at least 75% charged for the test.

The hydrostatic transaxle assembly procedure specifies 0.002–0.016 inches of axle end play, measured between the coupling and retaining ring for shim selection.