Ski-Doo Formula MX, Formula Plus & Formula Mach I Snowmobile 1985-1989 - Comprehensive Shop Manual

Ski-Doo Formula MX, Plus & Mach I Snowmobile Shop Manual - 1985-1989

This shop manual serves as the primary technical resource for the maintenance, troubleshooting, and complete overhaul of the specified Ski-Doo snowmobile models. To ensure maximum engine uptime, mechanics must pack a low-temperature grease into the oil seal lips prior to installation to maintain sealing integrity under extreme sub-zero operational parameters. Technical procedures within this document range from routine periodic lubrication to sophisticated engine and suspension system architecture restoration.

Technical Applicability & Model Identification

The following models are covered under the scope of this manual, identified by their primary four-digit vehicle model number:

• 1985 Series Configurations
  • 3720: Formula MX
  • 3721: Formula Plus
• 1986 Series Configurations
  • 3725: Formula MX
  • 3726: Formula Plus
  • 3727: Formula MX (H/A - High Altitude)
• 1987 Series Configurations
  • 3728: Formula MX
  • 3729: Formula Plus
  • 3730: Formula MX LT
• 1988 Series Configurations
  • 3732: Formula MX
  • 3733: Formula Plus
  • 3734: Formula MX LT
• 1989 Series Configurations
  • 3735: Formula MX
  • 3736: Formula MX LT
  • 3737: Formula Plus
  • 3738: Formula Plus LT
  • 3739: Formula Mach I

Performance & Operational ROI

• System Longevity: Adherence to factory-specified torque sequences prevents fastener failure and structural stress on aluminum components.
• Operational Safety: Detailed testing procedures for Capacitor Discharge Ignition (CDI) systems eliminate high-voltage hazards during diagnostics.
• Parts Accuracy: Precision measurement benchmarks for cylinder bore taper and out-of-round conditions ensure optimal compression and fuel economy.

Document Metadata

• Manual Type: Factory Shop Manual
• Applicable Years: 1985, 1986, 1987, 1988, 1989
• Measurement Standards: Dual Metric and U.S. Customary Units

Technical Depth & Factory Benchmarks

Rotary valve timing and ignition synchronization represent the critical calibration data for these powerplants. Piston-to-cylinder clearance and ring end gap specifications are provided for 462.8cc, 521.2cc, and 580.8cc engine variants to maintain factory-level power output. Detailed resistance values for primary and secondary ignition coils provide a definitive baseline for electrical system integrity.

Visual Navigation Aids

System architecture is illustrated through high-resolution technical drawings and photographs. This manual includes:

• Detailed exploded views of the RAVE (Rotax Automatic Variable Exhaust) system on 583 engines.
• Step-by-step photographic guides for primary and secondary sheave disassembly.
• Full-scale wiring diagrams for ignition, lighting, and sensor circuits.
• Internal cross-sections of fuel pump and carburetor assemblies.

Table of Contents

• Chapter One: General Information (Serial Numbers, Fasteners, Tools)
• Chapter Two: Troubleshooting (Engine, Electrical, Drive System)
• Chapter Three: Lubrication, Maintenance and Tune-up
• Chapter Four: High-Altitude and Rear Suspension Adjustment
• Chapter Five: Engine (Rotary Valve, RAVE, Crankcase)
• Chapter Six: Fuel and Exhaust Systems (Carburetor, Fuel Pump)
• Chapter Seven: Electrical System (CDI, Voltage Regulator)
• Chapter Eight: Oil Injection System
• Chapter Nine: Liquid Cooling System
• Chapter Ten: Recoil Starter
• Chapter Eleven: Drive System (Clutching, Belt Deflection)
• Chapter Twelve: Brake, Chaincase, Jackshaft and Drive Axle
• Chapter Thirteen: Front Suspension and Steering
• Chapter Fourteen: Track and Rear Suspension
• Chapter Fifteen: Off-Season Storage
• Appendix: Wiring Diagrams and Index

Operational Limits & Specifications

• Cylinder Head Torque: 20 N-m (15 ft.-lb.) for 1985-1988 models; 22 N-m (16 ft.-lb.) for 1989 models.
• Fluid Capacities: Cooling system requires 4.2 L (142 oz.) of a 60:40 ethylene glycol-based mixture.
• Lubrication Specification: Rotary valve reservoir (1985-1988) requires 455 cc (16 oz.) of specified lubricant.
• Ignition Gaps: Standard spark plug gap is 0.40 mm (0.016 in.) for most models, increasing to 0.45 mm (0.018 in.) for the Formula Mach I.