Oldsmobile Diesel Engine - LF9

The LF9 was a 350 cu in (5,737 cc) diesel V8 produced from 1978-1985.

Applications;

• 350N 1978–1985 Chevrolet, Buick, Oldsmobile, Pontiac, Cadillac, and Checker Marathon cars
  • Early 120 hp (89 kW) 220 ft·lbf (300 N·m) torque
  • Later 105 hp (78 kW) and 205 ft·lbf (278 N·m) torque

• 350N 1978–1980 GMC and Chevrolet light trucks "pickups"
  • 125 hp (93 kW) and 225 ft·lbf (305 N·m) torque

Variations;

• 1978–1980 Early block Identified by "D" cast into both sides of block
  • Up to 125 bhp (93 kW)
  • external EGR from 1978–1980 (single stud air cleaner)
  • internal EGR from 1981–1985 (two stud air cleaner)
  • Used a conventional flat tappet hydraulic camshaft/flat tappet hydraulic lifters which required 3,000 mi (4,800 km) oil change intervals.

• 1981–1985 Improved block Identified by "DX" cast into both sides of block.
  • Up to 105 bhp (78 kW)
  • Internal EGR
  • All 5.7 diesels from 1978–1985 used 1/2" diameter cylinder head bolts.
  • Longer main bolts with fully tapped holes in block.
  • Newly introduced roller lifters/rollerized camshaft extended oil change intervals to 5,000 mi (8,000 km).

Diesel differences;

The Oldsmobile diesel is believed by some to be a converted gasoline engine. While they share the same bore and stroke and some external bolt patterns (transmission and exhaust manifolds) they are completely different engines

GM began with a substantially different bottom end when compared with its gasoline cousin.

• Diesel blocks
  • 3" diameter injection pump mount is cast into the top of the lifter valley. This casting was part of the engine block.
  • Camshaft nose modified to incorporate injection pump drive gear.
  • A round plastic button in the 1981-1985 DX blocks was used with a stiff spring to prevent the camshaft from "walking" back and forth.
  • Block castings are much thicker and heavier. It's possible to overbore the cylinders by 0.125in without sonic testing.
  • Solid heavy cast main webs were used.
  • Reputedly, GM used a higher nickel cast iron alloy for the block and heads.

• Diesel crankshafts
  • Cast nodular iron used in all Olds diesel crankshafts.
  • Main bearing journal diameter was increased to 3.0" which made that area the same as that of the Olds 455 crankshaft.
  • Vibration damper modified to allow eccentric for crank-driven fuel lift pump.

• Diesel pistons and rods
  • Diesel rods are shorter at 5.886" long.
  • Diesel connecting rods use a bronze bushing with a full floating piston pin. They did not use press fit piston pins like many gasoline engines do.Snap-rings are used to retain the piston pin within the piston.
  • Diesel pistons have large valve reliefs with a flame slot and a steel insert to reinforce the top piston ring area.

• Fuel systems
  • No OEM fuel/water separator was factory installed on any Olds Diesel.
  • Crank eccentric driven fuel lift pump mounted in same location as gasoline fuel pump.
  • Fuel line heater between lift pump and filter.
  • Intake mounted 10 micrometer fuel filter.
  • Stanadyne Roosamaster DB2 mechanical diesel injection pump.
  • 1978-79 Pencil Injectors held in by a mounting clamp.
  • 1980-85 Poppet injectors thread into the cylinder head like a spark plug.

• Heads
  • The same 10-head bolt pattern as their smallblock gasoline cousins.
  • The same exhaust manifold bolt pattern as their smallblock gasoline cousins.
  • Precombustion chambers were used since this engine is a indirect-injected design.
  • Valve springs contained a vibration dampener with rotators.

• Head variations
  • Very early castings were stamped D3 and used 5/16" injector hold down retaining bolts and clamps.
  • D3A castings were created a little later and used 3/8" injector hold down bolts and clamps.
  • Both D3 and D3A heads accepted external EGR and pencil injectors.
  • Some D3A heads accepted poppet injectors as well.
  • D3B Later heads
    • All had internal EGR
    • Pencil or poppet injectors
    • 1 or 2 locating dowels

The Oldsmobile diesel gained a reputation for unreliability and anemic performance that badly damaged the North American passenger diesel market for the next 20 years. However, the strong blocks continue to see use in petrol-powered race engines.