Hispano-Suiza 12Mbr
| 12M | |
|---|---|
| Type | V-12 |
| National origin | France |
| Manufacturer | Société Francaise Hispano-Suiza |
| Designed by | Marc Birkigt |
| First run | 1927 |
| Unit cost | 240,000 FF (1931) |
The Hispano-Suiza 12M was one of two new V-12 engine designs first run in 1927-8. It produced about 375 kW (500 hp), was the first to use gas nitride hardening and introduced wet cylinder liners into Hispano-Suiza's aircraft engine range.
Up to 1927, Hispano-Suiza's many engine types, of various layouts and cylinder numbers, were all recognisable developments of the World War I V-8 Hispano-Suiza 8. 1927-8 saw the introduction of four completely new engines, two V-12s and two with six cylinders inline. The Hispano-Suiza 12M, known by the manufacturers as the Type 57, was the smaller of the V-12s, with a displacement of 27.0 L (1,648 cu in), the other being the 36.0 L (2,197 cu in) 12N. Apart from capacity and power, these two engines had much in common. The 12M first ran in 1927 and the 12N a year later.
Both 12M and 12N were 60° V engines with carburettors, inlets and exhausts on the outer faces. There were three carburettors per bank, each charging a pair of cylinders. Much of the new technology was in the cylinder design: these types introduced wet liners, an Hispano automobile engine innovation which brought the cooling water into direct contact with the steel cylinder barrel rather than by screwing it into an aluminium water jacket. This improved cooling, simplified assembly and allowed larger cylinder bores without increasing their separation. The cylinder barrels were open at top and bottom and threaded for screwing into the block only near the top, with valve seats ground into the aluminium cylinder head. The lower end of the barrel extended into the crankcase, simplifying both manufacture and assembly. Block and crankcase were bolted together.
The 12M and 12N engines were the first to use the gas nitriding surface hardening process on the cylinder walls, which reduced both wear and oil consumption. They also used a novel, complicated but effective method of main bearing cooling, enhancing the local lubricant flow without requiring high overall oil pump speeds.
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