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
|Displacement||2.5 L, 2,488 cc (151.82 cu in)|
|Injection pump||Diesel Kiki-Bosch (in-line or VE)|
|Max. Horsepower||70 HP (71 PS, 52 kW) at 4,000 rpm|
|Dimensions (L x H x W):||–|
|Cylinder block alloy||Cast iron|
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 alloy||Cast iron|
|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)|
|Nissan D21 Pickup||1986-1988|
SD25 Engine Problems
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.