1988 Honda TRX350D Service Manual

The 1988 Honda TRX350D is a four-wheel ATV featuring a 350cc four-stroke engine, electric start, shaft drive, independent rear suspension, and dual-range transmission. This comprehensive service manual covers maintenance procedures, specifications, troubleshooting, and repair instructions for proper servicing of your ATV. Below are key sections for safety, specifications, maintenance, troubleshooting, and repair procedures.

1. Specifications 2. Safety Precautions 3. Maintenance Schedule 4. Engine Service 5. Transmission & Drive System 6. Electrical System 7. Suspension & Steering 8. Brake System 9. Fuel System 10. Troubleshooting 11. Torque Specifications

Specifications

Detailed technical specifications for the 1988 Honda TRX350D ATV.

ComponentSpecification
Engine Type350cc 4-stroke OHC single cylinder
Bore x Stroke79mm x 71mm
Compression Ratio8.5:1
Fuel SystemKeihin 26mm carburetor
Starting SystemElectric start with auxiliary recoil
Transmission5-speed with reverse and dual-range sub-transmission
Drive SystemShaft drive
Suspension FrontIndependent double wishbone
Suspension RearIndependent rear suspension
Brakes Front/RearDual hydraulic disc / Single hydraulic disc
Fuel Capacity3.7 gallons (14 liters)
Dry Weight474 lbs (215 kg)

Safety Precautions

Essential safety guidelines for servicing your Honda TRX350D.

  1. Always work in a well-ventilated area when servicing fuel system.
  2. Disconnect battery before performing electrical work.
  3. Use proper lifting equipment when raising the ATV.
  4. Wear safety glasses when using compressed air or chemicals.
  5. Keep fire extinguisher nearby when working with fuel system.

WARNING! Gasoline is highly flammable - never smoke or use open flames near fuel system work. Always support ATV securely on stands when elevated.

Maintenance Schedule

Recommended maintenance intervals for optimal performance.

Service ItemEvery 100 miEvery 500 miEvery 1000 mi
Engine Oil Change✓✓✓
Oil Filter✓✓
Air Filter Clean✓✓✓
Spark Plug✓✓
Valve Clearance✓
Brake Fluid✓✓
Drive Shaft Boots✓✓✓
Wheel Bearings✓

NOTE: More frequent maintenance may be required under severe operating conditions.

Engine Service

Engine maintenance and repair procedures.

  1. Oil Change: Drain plug located bottom of crankcase, capacity 2.6 quarts with filter change.
  2. Valve Adjustment: Intake: 0.004 in (0.10 mm), Exhaust: 0.005 in (0.12 mm) - engine cold.
  3. Spark Plug: NGK DR8ES-L, gap 0.028-0.031 in (0.7-0.8 mm).
  4. Compression Test: Normal range 142-199 psi, minimum 128 psi.
  5. Cooling System: Check coolant level in reservoir, 50/50 mix recommended.

CAUTION! Always replace oil filter and drain plug crush washer during oil changes.

Transmission & Drive System

Transmission service and shaft drive maintenance.

  1. Transmission Oil: Capacity 1.7 quarts, change every 1000 miles.
  2. Sub-Transmission: Dual-range selector mechanism inspection and lubrication.
  3. Drive Shaft: Check boots for cracks and lubricate splines annually.
  4. Shift Mechanism: Adjust shift linkage if shifting becomes difficult.
  5. Reverse Operation: Ensure proper engagement of reverse gear mechanism.

NOTE: Use only Honda HP4 80W/90 gear oil in transmission and sub-transmission.

Electrical System

Electrical component testing and service procedures.

ComponentSpecification
Battery12V 14Ah, maintain fluid level
Charging SystemAC generator, 210W @ 5000 RPM
Starter12V 0.9 kW brush type
Spark PlugNGK DR8ES-L
FusesMain 30A, Sub 10A, 15A
Headlight12V 30/30W x2

TIP: Check all electrical connections for corrosion and tightness regularly.

Suspension & Steering

Suspension maintenance and steering system service.

  1. Front Suspension: Check ball joints and bushings for wear.
  2. Rear Suspension: Inspect swingarm bearings and pivot points.
  3. Shock Absorbers: Check for oil leaks and proper damping.
  4. Steering Stem: Adjust bearing preload if steering feels loose.
  5. Wheel Alignment: Check toe-in and camber settings.

WARNING! Always torque suspension nuts and bolts to specification for safety.

Brake System

Brake system maintenance and repair procedures.

  1. Brake Fluid: DOT 4, change every 2 years or 2000 miles.
  2. Brake Pads: Replace when worn to 1mm thickness.
  3. Brake Discs: Minimum thickness 3.5mm front, 4.0mm rear.
  4. Bleeding: Required after fluid change or system service.
  5. Parking Brake:Adjust cable tension for proper operation.

CAUTION! Never reuse brake fluid - always use fresh fluid from sealed container.

Fuel System

Carburetor service and fuel system maintenance.

  1. Carburetor Settings: Pilot screw 2-1/8 turns out, main jet #122, slow jet #38.
  2. Float Level: 12.5mm measured from carburetor body.
  3. Fuel Filter: Replace annually or every 1000 miles.
  4. Throttle Cable: Adjust for 2-3mm free play at throttle grip.
  5. Choke System: Ensure proper cable operation and enrichment circuit.

NOTE: Use only fresh gasoline and avoid ethanol blends when possible.

Troubleshooting

Common problems and solutions for the TRX350D.

SymptomPossible CauseCorrective Action
Hard startingDirty carburetor, weak batteryClean carburetor, charge/test battery
Poor performanceClogged air filter, bad spark plugReplace air filter and spark plug
Transmission noiseLow oil level, worn gearsCheck oil level, inspect transmission
Electrical failureBlown fuse, bad connectionCheck fuses and wiring connections
Brake dragStuck caliper, contaminated fluidClean calipers, flush brake system
OverheatingLow coolant, clogged radiatorCheck coolant level, clean radiator

Torque Specifications

Critical torque values for proper assembly.

ComponentTorque Value
Spark Plug13 ft-lbs (18 Nm)
Engine Oil Drain Plug22 ft-lbs (30 Nm)
Wheel Nuts65 ft-lbs (88 Nm)
Axle Nut87 ft-lbs (118 Nm)
Cylinder Head Bolts20 ft-lbs + 90° turn
Flywheel Nut87 ft-lbs (118 Nm)
Drive Sprocket Nut65 ft-lbs (88 Nm)
Brake Caliper Bolts23 ft-lbs (31 Nm)

IMPORTANT: Always use a calibrated torque wrench for critical fasteners.

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