SD25 Engine
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
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
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.
Written by Dan Hoffman
