ENGINE SPECS

1951 Mercury 255 V8 Engine Specs

GENERAL SPECIFICATIONS

Model Designation: 1M

Wheel base: 118

Valve Location: In block

Bore and Stroke: 3-3/16 x 4

Piston displacement, Cubic Inches: 255.4

Compression ratio: 6.80

Maximum Brake Horsepower: 112 @ 3600 RPM

Maximum Torque Lbs.Ft. @ RPM: 206 @ 2000 RPM

Normal Oil Pressure Pounds: 57

TUNE UP SPECIFICATIONS

Spark Plug Make: Champion H10

Spark Plug Gap, Inch: .030

Firing Order: 15486372 (front to rear: Right bank 1-2-3-4, left bank 5-6-7-8)

Timing Mark: Groove in Pulley

Engine Idle Speed, RPM: 475

Cylinder Head Torque Lbs.Ft.: 65-70

Compression Pressure & Cranking Speed: 115 Min.

Voltage & Polarity: 6 volts, positive ground

PISTON AND RING SPECIFICATIONS

Fitting Pistons with Scale: Pistons removed from above. Shim thickness: .002;

Pounds on a Pull Scale: 6 to 12

Ring End Gap: In tapered bores, fit rings in tightest portion of ring travel
Compression: .007
Oil: .010

Clearance in Groove: Compression: .0015-003; Oil: .0015-.003

Wristpin Diameter, Inch: .7501-.7504

VALVE SPECIFICATIONS

Operating Clearance:
Intake: .014 Cold Exhaust: .018 Cold

Valve Seat Angle, degrees: 45

Valve Timing: (BTDC = before top dead center; ATDC = after top dead center)
Intake opens: 5 BTDC
Exhaust Closes: 9 ATDC

Valve Spring Pressure Pounds at Inches Length:
Inner Spring: 40 @ 1.89

Valve Stem Clearance: Intake: .0015-.003; Exhaust: .002-.004

ENGINE BEARING SPECIFICATIONS

Connecting Rod Bearings:
    Journal Diameter, Inches: 2.1390
    Bearing Clearance, Inch: .0005-.003
    Rod End Play, Inch: .006-.020
    Rod Bolt Tension: Lbs.Ft.: 45-50

Main Bearings:
    Journal Diameter, Inches: 2.4985
    Bearing clearance: .001-.0026
    Shaft End Play: .002-.006    (Thrust on Rear Bearing)
    Main Bolt Tension: Lbs.Ft.: 90-105

CAPACITY DATA

Cooling System:
Without heater: 22 quarts
With heater: 23 quarts

Fuel Tank: 19-1/2 gallons

Engine Oil: 5 quarts

Transmission: w/out overdrive: 3-1/4 pints; w/overdrive: 4-1/4 pints; Automatic: 9 quarts

Rear Axle: 3-1/2 pints

LOADAMATIC DISTRIBUTOR SPECIFICATIONS

Distributor part number: 7RA-12127C (distributor rotates clockwise)

Cam Angle, degrees: 28

Breaker Point opening, Inch: .014-.016

Condenser Capacity: .21-.25 Mfds.

Breaker Arm Spring Tension: 17-20 Oz.

Vacuum Advance: (degrees at RPM of distributor)
    At 500 RPM: 1-1/4 - 2-1/4 Degrees advance; .4 Inches Vacuum
    At 1000 RPM: 4-1/2 - 5-1/4 Degrees advance; 1.7 Inches Vacuum
    At 1400 RPM: 6-1/4 - 7-1/4 Degrees advance; 2.8 Inches Vacuum
    At 2000 RPM: 7-1/2 - 8-1/2 Degrees advance; 3.7 Inches Vacuum

GENERATOR SPECIFICATIONS

Generator Number: 8BA-10000B (generator rotates clockwise, 6 volts, Positive Ground)

Generator output: 36 @ 1700 RPM

Brush Spring Tension: 30 oz.

REGULATOR SPECIFICATIONS

Regulator Number: 8M-10505A

Cutout Relay:
Voltage to close points: 6.3
Reverse current to open points: 0-8

Voltage Regulator Setting: 7.3 volts

Current Regulator Setting: 30 amps

STARTING MOTOR SPECIFICATIONS

Part number: 7RA-11001

Bush Spring Tension, Ounces: 48-56

No Load Test: 70 amps, 6 volts @ 3000 RPM

Torque Test: 700 Amps, 3.5 volts, Torque, Lbs.Ft.: 16

WHEEL ALIGNMENT SPECIFICATIONS

Caster, Degrees
Limits: -1 to +1/2
Desired: -1/4

Camber, Degrees
Limits: 0 to +3/4
Desired: +3/8

Toe-In, Inches: 3/32 to 5/32

Toe-Out on Turns, Degrees: (If toe-out is incorrect, when other adjustments are correct, look for bent steering arms.)
Outer wheel: 20
Inner Wheel: 23 to 24

Kingpin Angle, or Steering Axis Degrees: (If king pin or spindle support angle are incorrect, but camber is correct, look for bent suspension arms or steering knuckle support)
5 @ 3/4 Camber