Honda C65, C65M, S65 Factory Service Manual (P/N 07900-1180000)

• Covers the Honda 50 series C50, C50M, S50, and C50MK1 and the Honda 65 series C65, C65M, and S65, followed by Honda's CL70/C70/C70M supplement. Honda notes that the 70-series supplement uses the 50/65 material for detailed fundamentals, so the base repair information and the model-specific supplement are together in this PDF.
• Factory shop manual issued by Honda Motor Co., Ltd., Service Publications Office. This PDF contains 156 pages of specifications, service procedures, inspection data, troubleshooting tables, performance charts, and wiring diagrams. Honda Tool Set No. 07900-1180000 is specified for C65/S65 and carried over to the CL70/C70/C70M supplement.
• Separates the engine and drivetrain configurations instead of treating the models as mechanically identical. C50/C50M/C65/C65M/C50MK1 use 3-speed constant-mesh gearsets, while S50/S65 use 4-speed gearsets. The CL70 supplement specifies a 4-speed transmission and wet multi-plate clutch; C70/C70M use 3-speed transmissions with automatic centrifugal wet multi-plate clutches.
• Gives hard engine specifications for the 49 cc C50/C50M/S50/C50MK1 and 63 cc C65/C65M/S65 engines, plus the 72 cc CL70/C70/C70M O.H.C. engines. The main 50/65 specification table lists a 0.8 L lubrication-system capacity for the base models, while C50MK1 and the 70-series specifications use 0.7 L.
• Includes Honda special-tool identification rather than generic tool references. Examples include tappet wrench set 07908-0010000, clutch assembly tool 07960-0110000, flywheel holder 07925-0010000, flywheel puller 07933-0010000, and rear-cushion disassembly tool 07959-3290000.
• Named technical views include the Pressure Lubrication Diagram, Oil Pump Theory of Operation, Cam Chain Tensioner Detail Diagram, Carburetor Cross Section Diagram, A.C. Generator Performance Chart, and model-specific wiring diagrams for C50/C65, C50M/C65M, S50/S65, CL70, C70, and C70M. The C70M electrical drawings separately cover General Export and U.S.A. Type configurations.

Engine, Transmission, and Chassis Technical Details

The engine section covers engine removal and installation, cylinder-head disassembly, valve-seat and valve-guide inspection and repair, cylinder and piston measurement, piston-ring service limits, camshaft and crankshaft inspection, the oil-damped cam-chain tensioner, clutch repair, transmission disassembly and inspection, kick starter service, and carburetor adjustment. Lubrication coverage shows the gear-type oil pump, oil routes, screen, and centrifugal filter rather than only listing an oil quantity.

Carburetion is split between the C50/C50M/C65/C65M group and the S50/S65 group. A model-by-model carburetor setting table records carburetor type, throttle and venturi bore, main and air jets, needle and slow-jet calibration, pilot-circuit data, valve seat, and fuel-level height. This is particularly relevant when a motorcycle has acquired mismatched jets or carburetor parts during previous repair work.

Factory limits are given where measurements determine whether a part can be reused. Examples include a 3.5 mm clutch friction-disc thickness with replacement below 3.1 mm and rear brake lining at 3.5 mm standard with replacement below 1.5 mm. Wheel and axle inspection includes dial-gauge runout and bend limits. The 70-series tightening table specifies 27.5-32.5 lb-ft (380-450 kg-cm) for the clutch nut, 23.9-27.5 lb-ft (330-380 kg-cm) for the CL70/C70 flywheel, and 15.9-21.7 lb-ft (220-300 kg-cm) for the C70M rotor.

Chassis coverage includes front and rear wheel service, internal-expanding brakes, drive chain, steering, air cleaner, frame body, front cushion, rear cushion, and muffler. The manual distinguishes the S50/S65 pressed-sheet-steel frame and its bottom-link front/swing-arm rear suspension from the CL70 T-bone frame with telescopic fork and the C70/C70M backbone frame with bottom-link front suspension.

Electrical, Maintenance, and Diagnostic Data

The 6V electrical material includes charging-system checks, flywheel A.C. generator and ignition-coil specifications, spark-advancer data, battery service, spark-plug diagnosis, lighting, horn, selenium rectifier testing, and speedometer troubleshooting. Periodic adjustment data specifies 12 kg/cm² (170 lb/in²) as standard compression pressure and treats readings below 9 kg/cm² (128 lb/in²) as a low-compression condition requiring further diagnosis. Intake and exhaust tappet clearance is 0.05 mm (0.002 in.) on the listed C50/C50M/C65/C65M/S50/S65 engines, and spark-plug gap is 0.6-0.7 mm (0.024-0.028 in.).

The selenium-rectifier section gives component-specific handling cautions. Honda warns against bending, cutting, scratching, or rotating the selenium wafers or locking hardware because electrode movement and loss of moisture sealing shorten rectifier life. It also warns not to run the engine with the battery or electrical load disconnected; the resulting open-circuit high voltage can puncture the selenium rectifier. The 70-series electrical data adds resistance targets of less than 15 ohms forward and more than 1,500 ohms reverse per rectifier element.

Two other assembly details are easy to miss during repair work. The right-crankcase-cover gasket must not be damaged or installed out of alignment. The piston is directional, with its crown arrow facing forward, and Honda specifies piston-pin clip orientation and replacement of clips that have lost tension; incorrect clip retention can allow movement at the piston pin and risk internal cylinder damage.

Factory procedures cover the jobs that often send these motorcycles to a specialist: engine removal, cylinder-head and valve work, clutch and transmission repair, cam-chain tensioner service, carburetor setting, wheel and brake inspection, rear-cushion work, ignition and charging diagnosis, and rectifier testing. Brake, wheel, fuel-system, and live electrical work directly affect roadworthiness and safety; use the stated wear limits, tightening values, and test conditions before returning the motorcycle to service.