|Configuration||V12 or V16 four-stroke turbo-charged high-speed diesel|
|Displacement||80.5 litres (5,000 cu in) (V12)
107 litres (7,000 cu in) (V16)
|Cylinder bore||7.75 inches (197 mm)|
|Piston stroke||8.5 inches (220 mm)|
|Power output||1,200–1,400 brake horsepower (890–1,040 kW) at 1,500 rpm (V12)
1,600–1,870 brake horsepower (1,190–1,390 kW) at 1,500 rpm (V16)
|Predecessor||Paxman YH, direct injection medium-speed diesel|
The type YJ or Ventura was developed in the mid-1950s as Davey, Paxman's first high-speed diesel engine. With a view to the forthcoming modernisation and dieselisation of British Railways, it was intended as a successor to Paxman's existing medium-speed engine, the direct injection YH. High-speed engines offered higher power-to-weight ratios, which in turn allowed locomotives to have a lower axle loading and greater route availability. Their construction and reliable use though required more sophisticated manufacture than previously, with better metallurgy and balancing of the moving parts for faster running and a stiffer crankcase to avoid vibration.
Like its medium-speed predecessor the Paxman YH, the Ventura is a 60° V engine with either 12 or 16 cylinders. The engines are similar in many details and broadly similar in capacity and power; their main differences are in their operating speed, the improvements necessary to achieve this, and the Ventura's resulting lighter weight.
The crankcase and cylinder block are fabricated from steel by welding a mixture of steel castings and platework. This gives a more rigid structure than the YH's cast light alloy block. The aluminium frame of the YH and ZH engines had previously given trouble with cracking and had to be replaced in the Class 17 with a cast iron frame, at Paxman's expense. Both engines have individual aluminium cylinder heads for each cylinder. Centrifugally cast iron wet cylinder liners are used with aluminium pistons in both. These pistons have three compression rings and two oil-control rings. The top ring is carried in a cast iron insert. The combustion chamber of this direct injection engine is a toroidal recess in the piston crown.
Both engines were developed for diesel electric locomotives and so their crankshafts have the unusual feature of an additional main bearing at the drive end, to help support the weight of the generator armature, where a single-bearing generator can be otherwise unsupported at one end.
There are four valves per cylinder, driven by pushrods and rockers from a single camshaft between the cylinder banks. The fuel injector is centrally mounted between the valves, and is supplied by a pair of inline fuel injection pumps, one per bank.
Smaller, single bank six- and eight-cylinder engines, the 6YJ and 8YJ, were derived from the V engine.
- Class 29
- Class 42, two units fitted from new to D830 Majestic for comparison trials. Units rated at 1200 BHp and allied to normal Class 42 spec Mekydro transmissions.
Type 42 destroyer, as a set of four generator sets, each rated at 1 MW.