SD25 Engine


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SD25, a variation of Nissan SD engines, is a 2.5L (2.488 cc) inline-4 diesel motor with water cooling.

Having compression index of 20.7 and 21.4 for Datsun and Nissan (non-California) and 21.9 for these vehicles within California standards, motor’s output is 70 hp (71 PS, 52 kW) at 4,000 rpm.

SD25 is the largest motor from the 4-cylinder SD range with 5 main bearing crankshaft and modernized rear main seal, constructed primarily for Nissan 720 (1983-1986) and Nissan D21 (1986-1988) vehicles. But, Nissan Urvan and Cabstar utilized it as well.

Depending on automobile mode and where it was sold, SD25 featured Kiki-Bosch in-line fuel or VE fuel injection pump.

All-in-one cylinder block with strong cast-iron construction keeps commutable dry liners. Moreover, motor features 5 main bearings of precision type with steel trimetal body, iron-shod steel crankshaft featuring balance weights plus induction-hardened rods.

Engine gained aluminum alloy piston, which is strong, lightweight and has great heat conductivity; 1 oil control and 2 compression rings with chrome plating for better endurance. Cylinder bore is 89 mm (3.50 inches) while piston stroke is 100 mm (3.94 inches).

With solid and strong cast-iron cylinder head and shrink-mounted cast-iron valve sleeves, SD25 is provided with qualitative cast-iron camshaft with lobes, developed to enhance endurance and rigidity.

SD 25 features OverHead Valve construction with 1 intake and 1 exhaust heat-resistant steel valves for each cylinder. Intake valves have diameter of 40 mm and exhaust ones (featuring stellite-processed exterior) are 34 mm.

The breakdown of the engine code is as follows:

  • SD – Engine Family
  • 25 – 2.5 Liter Displacement

Nissan SD25 Specs

Engine code SD25
Layout Straight-4, vertical
Fuel type Diesel
Production
Displacement 2.5 L, 2,488 cc (151.82 cu in)
Injection pump Diesel Kiki-Bosch (in-line or VE)
Power adder None
Max. Horsepower 70 HP (71 PS, 52 kW) at 4,000 rpm
Torque output
Firing order 1-3-4-2
Dimensions (L x H x W):
Weight
Cylinder block
Cylinder block alloy Cast iron
Compression ratio: 20.7:1
21.4 (only for Datsun/Nissan 720 Pickup, Non-California)
21.9 (only for Datsun/Nissan 720 Pickup, California)
Cylinder bore: 89 mm (3.50 in)
Piston stroke: 100 mm (3.94 in)
Number of piston rings (compression / oil): 2 / 1
Number of main bearings: 5
Block Height: 268.00 mm (10.55 in)
Cylinder liner inner diameter: 89.000-89.035 mm (3.5039-3.5053 in)
Piston skirt diameter 88.895-88.935 mm (3.4998-3.5014 in)
Piston ring side clearance: №1 0.06 – 0.010 mm (0.0024 – 0.0039 in)
№2 0.04 – 0.08 mm (0.0016 – 0.0031 in)
№3 0.02 – 0.06 mm (0.0008 – 0.0024 in)
Piston ring end gap: №1 0.30 – 0.45 mm (0.0118 – 0.0177 in)
№2 0.20 – 0.35 mm (0.0079 – 0.0138 in)
№3 0.15 – 0.30 mm (0.0059 – 0.0118 in)
Piston pin outer diameter 25.993-26.000 mm (1.0233-1.0236 in)
Piston pin bore diameter 26.025-26.038 mm (5.5295 – 5.5335 in)
Connecting rod center distance: 170.0 mm (6.69 in)
Crankshaft journal diameter: 70.907-70.920 mm (2.7916-2.7921 in)
Crankpin diameter: 52.913-52.926 mm (2.0832-2.0837 in)
Crankshaft center distance: 50.00 mm (1.9685 in)
Cylinder head
Cylinder head alloy Cast iron
Valve Arrangement: OHV
Valves: 8 (2 valves per cylinder)
Intake valves diameter: 40.0 mm (1.575 in)
Exhaust valves diameter: 34.0 mm (1.339 in)
Valves length: 117.0 mm (4.61 in)
Intake valve stem diameter: 7.970-7.985 mm (0.3138-0.3144 in)
Exhaust valves stem diameter: 7.945-7.960 mm (0.3128-0.3134 in)
Camshaft journal diameter: Front:45.434-45.447 mm (1.7887-1.7892 in)
Center:43.897-43.910 mm (1.7282-1.7287 in)
Front:41.218-41.231 mm (1.6228-1.6233 in)
Cam height: 37.28-37.32 mm (1.4677-1.4693 in)

Engine Applications

Model Years Produced
Nissan 720 1983-1986
Nissan D21 Pickup 1986-1988

SD25 Engine Problems and reliability

SD motors are known for their reliability and great durability. Moreover, they don’t demand much service. Thanks to its industry-standard BOSCH injection system parts, constructed under license by Diesel Kiki, SD25 has almost no problems and can serve for many years.




Dan Hoffman

Dan is a co-founder of Engineswork. He knows everything about internal combustion engines. Ask your questions in comments down below this article - he will be glad to help you anytime.

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