1957 Maserati 250F 2.5-litre six
1957 Maserati 250F 2.5-litre six: The cylinder block extended from centerline of crankshaft to top of cylinders, which were capped by a detachable cylinder head, the top 1/3rd of the block served as an aluminum-alloy coolant tank surrounding 6 nitrided–iron wet cylinder liners, the lower 2/3rds of the liners were a shrink-fit in the block.
7 main bearing caps each had 4 retaining studs. A fully-counterweighted nitrided-steel crankshaft machined from a billet was used.
A deep casting at front bolted to the assembled block-sump unit carried the scavenge and pressure oil pumps, water and mechanical fuel Mona pumps + the helical and spur gear drives to these units and also all fluid inlet and outlets. At front the crank carried 2 helical gears, 1 to drive this unit and the other to drive the gear train in the block. The latter consisted of 2 big drilled gears vertically disposed to drive the 2 pairs of cam-drivegears in the head, plus 2 short longitudinal shafts with bevels which drove the 2 Marelli magnetos.
Very deep Electron sump was divided by a bulkhead into 2 separately-scavenged sections, a longitudinal baffle placed at an angle scooped oil splash off the crank and directed it downwards. The scavenge pump drew from 2 pick-ups. Oil pressure was at 100-110psi. Oil entered the center main bearing from the left and passed on the right hand side. This fed the rest of the mains. BP produced a special SAE 40 oil specifically for this engine, “BP Corsa 40”.
All bottom end bearing shells were Vandervell lead-indium type. The front and rear main bearings were 32mm wide while the 5 inner once were 19mm wide.
I-section forged steel rods with 2 bolts per cup were fully polished with bronze gudgeon pin bushings. The full skirt pistons were made by Borgo and had 2 compression rings and 1 oil ring above the pin + 1 oil ring below it, the rings were by Kiklos.
Helical timing gears all the way up to last idler, shared a shaft with spur-gear that drove camshafts, each cam had 7 babbit bearings.
Pivoted fingers between lobes and valve stem were used. 3 coil springs exerting 136kg closed each valve. Inlet valve inclined 36 degrees from vertical and exhaust 41 degrees. Valve lift was 8mm. 14mm spark plug were used. 3 Weber 45 DCO3 carburettors were used.
Desmodromic valve gear was built and tested as was fuel injection using an OM diesel injection pump with nozzles placed just at top of cylinder wall spraying against the inlet valve, but never raced.
Few engines have been granted a more classic racing status than this Maserati 250F GP racing engine.
Stroke/bore ratio 0.89:1.
Compression ratio 12.5:1.
Con-rod length 143mm.
Rod/crank radius ratio 3.8:1.
Main bearing journal 60mm.
Rod journal 51mm.
Inlet valve 46mm.
Exhaust valve 40mm.
Valve lift 8mm.
Inlet pressure 1Atm.
Engine weight 197kg.
Peak power 290BHP@7500RPM.
Piston speed corrected 19.5m/s.
Peak torque 286Nm@6000RPM.
Peak BMEP 208PSI.
116.3BHP per litre.
0.68kg per BHP.
It is not white, it is not black, it is probably gray.