1987 Mercruiser 260 Service Manual

The 1987 Mercruiser 260 is a marine stern drive engine with 5.7L V8 configuration, 260 horsepower, Thunderbolt IV ignition system, Alpha One stern drive, hydraulic trim system, and electric shift. This service manual covers maintenance procedures, troubleshooting, repair instructions, and specifications for the complete engine and drive system. Below are key sections for safety, specifications, maintenance, troubleshooting, and repair procedures.

Engine Specifications

Complete technical specifications for the 1987 Mercruiser 260 engine and drive system.

Safety Precautions

Critical safety information for working on marine engines and stern drives.

1. Disconnect battery before performing any electrical work.
2. Use proper lifting equipment for engine removal.
3. Work in well-ventilated areas when handling fuel.
4. Wear safety glasses during all maintenance procedures.
5. Use marine-grade parts and lubricants only.

WARNING! Marine engines present unique hazards including carbon monoxide, fuel vapors, and moving parts. Always follow proper safety procedures.

Maintenance Schedule

Recommended maintenance intervals for optimal performance and longevity.

1. Every 100 hours: Change engine oil and filter
2. Every 200 hours: Replace fuel filter, inspect spark plugs
3. Every 300 hours: Check timing, adjust carburetor if needed
4. Annual: Change stern drive gear lube, inspect bellows
5. Every 2 years: Replace water pump impeller
6. Every 5 years: Replace engine coupler, inspect manifolds

NOTE: More frequent maintenance may be required in saltwater or heavy use conditions.

Fuel System

• Carburetor: 4-barrel marine carburetor with anti-siphon protection
• Fuel Pump: Mechanical, engine-driven
• Fuel Filter: Replace every 200 hours or annually
• Fuel Requirements: 87 octane minimum, ethanol blends up to 10%
• Adjustments: Idle speed 650-700 RPM in neutral
• Float Level: Set to manufacturer specifications

Ignition System

Thunderbolt IV electronic ignition system with distributor, coil, and control module.

Components: Distributor, ignition coil, spark plug wires, control module, trigger assembly.

Timing: 8° BTDC at idle (in gear), 28° BTDC total advance. Spark Plugs: AC-MR43T or equivalent, gap 0.035". Coil Resistance: Primary 1.0-1.3 ohms, Secondary 8,000-11,000 ohms. Module Testing: Follow manufacturer procedure using multimeter.

Cooling System

Fresh water cooling system with raw water pump and heat exchanger.

1. Raw water pump: Replace impeller every 2 years or 300 hours
2. Thermostat: Opens at 143°F (62°C)
3. Pressure test: Check for leaks at 15 psi
4. Flush system after saltwater use

Tip: Always check water intake for debris before starting engine.

Stern Drive

Alpha One stern drive with hydraulic trim and electric shift.

1. Gear lube: Use only Quicksilver High Performance Gear Lube
2. Trim system: Check fluid level, bleed air from cylinders
3. Bellows: Inspect annually for cracks or deterioration
4. U-joints: Check for wear and proper lubrication
5. Shift cable: Adjust for proper engagement
6. Anode replacement: Inspect and replace as needed

WARNING! Never operate stern drive with damaged bellows or insufficient gear lube.

Electrical System

12-volt DC system with alternator, starter, and marine-grade wiring.

Troubleshooting

Common problems and solutions for the Mercruiser 260.

Torque Specifications

Critical torque values for engine and stern drive components.

• Cylinder heads: 65 ft-lbs in sequence
• Main bearing caps: 80 ft-lbs
• Rod bearing caps: 45 ft-lbs
• Flywheel: 75 ft-lbs
• Manifold bolts: 30 ft-lbs
• Spark plugs: 15 ft-lbs
• Propeller nut: 55 ft-lbs
• Drive shaft nut: 150 ft-lbs

Parts List

Common replacement parts and their Mercury Marine part numbers.

Service: Contact authorized Mercury Marine dealer for parts and technical support.