OM05

The board approved it on 28 September 1925, and Hans Nibel and Fritz Nallinger were handed the brief: cylinders of 105 × 165 mm, 85 PS at 1,300 rpm, fuel consumption of 200 to 220 grams per PS-hour. Two things made it buildable. One was the pre-chamber combustion process Benz had developed, which the new Daimler-Benz interest group chose over the alternatives; the other was the compressor-free inline injection pump Bosch put into production in 1928. Shown at Cologne in May 1927 in the five-tonne L 5, it became the first large-scale-production diesel lorry engine in the world.

The advertised figure was 75 PS. Customers never got it. Running a mean effective pressure of 5.6 bar — enough to make it the highest specific-output four-stroke diesel on the German commercial market in 1928 — brought what one account called unmanageable difficulties and reduced piston life; Theo Delfried Domina read it as straightforward thermal overload. Daimler-Benz retreated to 4.74 bar and 60 PS, still at 1,300 rpm, and sold it that way. Rated speeds soon climbed past 2,000 rpm and left it behind, but its architecture survived in the uprated OM 65 and OM 67.