1969–1982 Honda ST50, ST70, and CT70 Series Shop Manual (P/N 620401)
130 Pages • 24.36 MB • Instant, Printable PDF
Honda Models Covered & Key Technical Specifications
Models: ST50, ST70, CT70, 70H, CT70K1, CT70K2, CT70K3, CT70H, CT70HKI, CT70K4, CT70K6, CT70K7, CT70 Z, CT70 A, CT70 B, CT70 C
Sub-models / Variants: England type, General type, U.S.A. type, General Export type
Model Years: 1969–1982 (1969, 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982)
Serial Numbers: ST50 111528~, ST70 108801~, ST70 505971~, ST70 137314~, CT70H 100001~, CT70HKI 2000001~, CT70 100001~, CT70K1 2000001~, CT70K2 2100001~, CT70K3 2300001~
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Engine displacement: 72 cc (4.4 cu in)
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Bore and stroke: 47 × 41.4 mm (1.85 × 1.63 in)
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Compression ratio: 8.8:1
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Crankcase oil capacity: 0.8 L (0.17 US qt)
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Maximum horsepower: 4.0–5.6 hp at 8000 rpm
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Maximum torque: 0.50–0.87 kg·m at 4000–8000 rpm
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Ignition type: Flywheel magneto
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Transmission: 3-speed or 4-speed constant mesh
Honda Manual Features & Content Preview
- 130-page PDF covering Honda ST50, ST70, CT70 and CT70H minibikes, combining the base shop manual with CT70 addenda through 1982.
- Engine procedures cover removal and installation, cylinder-head repair, valve-guide replacement, oil-pump inspection and cam-chain tensioner service.
- 3-speed and 4-speed transmissions have separate gear-position diagrams, supported by clutch inspection, gear-shift mechanism checks and kick-starter assembly instructions.
- Chassis repair extends to steering-head bearings, wheel hubs, drum brakes, swingarm bushings and front and rear suspension.
- Electrical diagnosis includes A.C. generator charging tests, ignition-coil testing, condenser inspection, silicon-rectifier checks and switch-continuity charts.
- Keihin piston-valve carburetor sections provide exploded views, jetting tables, overhaul procedures, float-level checks and high-altitude adjustments.
Whether you are restoring a classic CT70 or maintaining an ST50 for weekend rides, this manual outlines the factory specifications needed for the job. It is suited to mechanics familiar with standard workshop procedures and equipped for engine measurement and electrical testing.
ST/CT variants and CT70 production changes
The base manual identifies UK ST50E and ST70E models, General Export ST70D I and D II versions, and US CT70, CT70K1, CT70K2, CT70K3, CT70H and CT70HK1 models. The H/HK1 material covers the manual clutch and 4-speed transmission; the standard CT70 uses the centrifugal clutch and 3-speed transmission.
Later sections cover CT70K4, K6/'77, K7/'78, Z/'79, A/'80, B/'81 and C/'82. Two supplements identify specific starting frame numbers:
| CT70 supplement | Applicability |
|---|---|
| K6 / 1977 | Frame No. CT70-2600008 and subsequent |
| K7 / 1978 | Frame No. CT70-2700005 and subsequent, manufactured before February 1978 |
The US emissions-related procedures in the 1979 addendum apply to machines manufactured after December 31, 1977. They cover the factory-set carburetor and closed crankcase-breather system, with a flow diagram showing the breather separator and storage tank.
Keihin carburetor revisions
The later carburetor sections identify these units:
| CT70 supplement | Carburetor identification |
|---|---|
| 1978 | PB36A |
| 1980 | PB37B |
| 1982 | PB16A |
The 1982 fuel-system instructions add fuel-strainer service and passage and jet cleaning.
The 1980 US pilot-screw procedures address the limiter cap and warn that forcing it off can break the screw. High-altitude information includes the applicable main-jet selections and the adjustments required when returning to lower elevations.
1980–1982 suspension and engine changes
The 1980 addendum documents the revised oil-filled front forks, with oil-seal replacement, fork-tube runout inspection and reassembly procedures, plus service for the revised rear shocks. Its fork-service cautions identify the sliding surfaces as vulnerable to damage from improper clamping.
The 1981 material covers VIN and frame-number locations, battery ventilation and harness routing. For 1982 engine repair, the supplement adds oil-pump drive engagement details, cylinder-head and valve assembly illustrations, camshaft inspection limits and piston-ring installation guidance.
Wear limits, 6V tests and service tools
The technical data sections list horsepower and torque ratings at specified RPM, gear ratios and fluid capacities. Inspection tables cover valve-seat dimensions, piston-ring clearances, crankshaft runout and connecting-rod bearing play. The Tightening Torque Limits table lists major engine fasteners; chassis torque specifications appear with the relevant service procedures.
For electrical diagnostics, the manual covers 6V bulb specifications, flywheel magneto reference values, and ignition coil outputs. The CT70H US and CT70 '82 wiring diagrams provide wire-color keys and switch-connection information. CT70 '80 cable-routing views show the control-cable and wiring-harness paths.
Special-tool lists identify equipment for the repair work, including flywheel puller 07933-0010000 and clutch outer holder 07923-0400000.
Companion manual required for referenced procedures
The base manual is designed to be used with the 50/65 Shop Manual, Code No. 620401. It cross-references that publication for shared engine and carburetor procedures and the separate Periodic Adjustment and Trouble Shooting chapters. The 50/65 manual is not included in this PDF.
Always verify standard wear limits and use the correct torque specifications before reassembling critical engine components.
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