1998 Clark CMP 15/18/20/25/30 Forklift Service Manual (P/N SM 638)

Clark publication SM 638, Revision 1 (October 1998) covers the 1998 CMP 15, 18, 20, 25, and 30 industrial forklifts. It addresses Mitsubishi 4G63 and 4G64 engines, with LPG configurations across the range and gasoline configurations for CMP 20/25/30.

• Engine repair: Engine removal, cylinder-head service, timing-belt installation, internal inspection, and overhaul specifications for pistons, crankshaft, and silent shafts.

• Fuel and cooling: LPG carburetor and vapor-regulator overhaul, gasoline carburetor service, fuel-pump replacement, and cooling-system troubleshooting.

• Transaxle service: Powershift transmission diagnosis, clutch-pack and differential overhaul, bearing-preload adjustment, and ring-and-pinion backlash and tooth-contact checks.

• Steering and hydraulics: Hydrostatic steering-unit, load-sensing priority-valve, steering-cylinder, hydraulic gear-pump, and main-control-valve overhaul procedures.

• Brakes and wheels: Internal expansion duo-servo drum brakes, brake and inching-circuit bleeding, parking-brake adjustment, and cushion and pneumatic wheel service.

• Uprights and chains: Mast and carriage shimming, standard and full free lift mast adjustments, lift-chain service, and lift- and tilt-cylinder overhaul.

• Electrical diagnosis: Circuit wiring diagrams, ignition troubleshooting, distributor service, starter bench tests, alternator overhaul, and instrument-pod identification.

This manual is written for trained service personnel working on industrial lift trucks.

Planned Maintenance and Engine Overhaul

The maintenance schedules identify service tasks and lubrication points by operating hours, with provisions for severe or extreme operating conditions. The PM Inspection Form provides a record of truck condition and follow-up repairs. Safe lifting, jacking, blocking, and towing procedures cover workshop preparation.

Engine removal and installation are documented separately from internal overhaul. The internal overhaul chapter is labeled 4G63 Gas & LPG, while the general engine specifications distinguish both engines.

The overhaul material includes piston clearances, ring end gaps, silent-shaft bearing tolerances, cylinder-head and valve inspection, and crankshaft-bearing selection. Timing Belt exploded views accompany the installation material. Permanently yielding bolt requirements and form-in-place gasket instructions address reassembly details; lash-adjuster testing identifies the MD998440 leak-down tester and MD998442 air bleed wire.

Fuel, Cooling, and Ignition Diagnosis

The LPG section explains the vacuum-operated lock-off, vaporizer-regulator, and mixer arrangement. Gasoline coverage adds float-level and choke checks, fuel cut-off solenoid testing, and mechanical fuel-pump removal and installation. Cooling-system troubleshooting addresses overheating, coolant contamination, and water-pump faults.

The Vacuum Gauge Readings chart and stall-test analysis help distinguish poor engine performance from torque-converter or clutch problems before major components are removed. Ignition diagnosis includes spark and insulation tests, centrifugal and vacuum advance checks, and coil-resistance testing.

Powershift Transaxles and Brake Service

The transaxle chapter provides separate specifications for TA-12 and TA-18 Hydratork units. Internal procedures cover forward and reverse clutch assemblies, differential setup, wheel-end bearing adjustment, and ring-and-pinion contact inspection.

Transmission pressure-check illustrations identify test connections. The manual cautions that prolonged stall testing can overheat and damage the converter, seals, and fluid.

Brake coverage distinguishes the service-brake and inching circuits, including separate bleeding procedures and pedal adjustments. Wheel service addresses cushion tires and pneumatic single- and dual-wheel assemblies.

Load-Sensing Hydraulics and Mast Adjustments

The Hydraulic Schematic and steering-system schematic show the relationship between the priority valve, steering unit, main control valve, and cylinders. Troubleshooting charts address heavy steering, steering-wheel motoring, pump cavitation, and loads that will not hold.

Mast procedures distinguish standard, full free lift two-stage, and full free lift three-stage arrangements. They cover roller shimming, cylinder racking, chain tension, and fork inspection. The manual warns that a reversed flow-limiting valve cannot protect against uncontrolled carriage descent after a hose failure.

For work involving raised mast sections, pressurized hydraulics, or heavy assemblies, follow the manual's blocking, pressure-release, and lifting precautions.

A Preview of Ignition and Fuel Test Data

These examples are a small selection of the tune-up and electrical specifications in the manual. The spark-plug gap is 0.7–0.8 mm, and ignition-coil primary resistance is 1.18–1.32 ohms between the positive and negative terminals.

For the gasoline carburetor's fuel cut-off solenoid, the resistance-check specification is approximately 90 ohms at 20°C (68°F). The related sections pair these values with inspection and fault-finding procedures.

Text Search, Bookmarks, and Diagram Detail

Search and drawing readability: Body text has an OCR search layer, and embedded PDF bookmarks cover the main groups and many subsections. Some tables and diagram labels are not searchable. The sideways wiring diagrams require rotation and zooming; some small wire codes and terminal labels remain difficult to read.

Supplied as one printable, English-language 281-page PDF. The original cover, introductory pages, contents, and conversion chart are already included in that total.