|This article needs additional citations for verification. (February 2010)|
|Configuration||V12 four-stroke turbo-charged & intercooled diesel|
|Displacement||79 litres (4,800 cu in)|
|Power output||2,250 brake horsepower (1,680 kW) at 1,500 rpm|
The Paxman Valenta was an engine that was made by Paxman diesels for the HST (British Rail Class 43 (HST)), and is still in use in various marine applications, such as the Upholder/Victoria class submarine.
The engine as originally fitted to the HSTs was designated 12RP200L and was a V12 four-stroke turbo-charged & intercooled diesel unit of 79 litres which develops 2,250 bhp at 1,500 rpm. The design of the Valenta was based on the Ventura which was fitted to the BR Class 29 diesel locomotives, amongst others.
Since 2005, Paxman Valenta-engined HST power cars have been refurbished with MTU16V4000 engines(except power cars operated by East Midlands Trains which are fitted with Paxman VP185 engines). There is no longer a Class 43 power car still fitted with a Paxman Valenta engine.
Around 20 November 2010, a Riding Inspector reported that the engine of powercar 43084 was blowing oil from the breather vent and crankcase door joints. The Paxman Service Engineer N Swager investigated the problem at the Heaton Maintenance Depot on 24 November. He examined the engine, number S468, and found that cylinder B-2 had low compression. A-2 piston and con rod assembly were first removed to gain access to the big end bearing block of B-2 cylinder. When B-2 piston was removed, it was found to be damaged and had some broken piston rings. This was the cause of S468 blowing oil due to combustion gasses pressurising the crankcase. A new piston was sent from the Paxman factory at Colchester; a new cylinder liner was also fitted from the spares stock at Heaton, and powercar 43084 returned to service. Powercars, 43084 and 43123 were the last two Valenta-engined powercars in service. They were taken out of traffic on 22 December 2010, after 4 farewell tours between York and Sunderland. They have since been fitted with MTU 16V4000 engines.
In May 2011, it was announced that the 125 Group would return prototype HST powercar 41001 to service. The powercar, currently on static display in the York National Railway Museum, will receive a full overhaul subject to technical assessment on both the vehicle and component parts. The overhaul is expected to pay particular attention to cooler group, bogies and electrical and electronic components.
The powercar will also receive installation of production Paxman Valenta RP200L engine Number S508 (installed new into 43153 in 2001 under Virgin CrossCountry, before re-installation to 43143 of First Great Western after a spell in storage), donated to the NRM from the MTU re-power programme. This will mark a sooner return to traffic of a Paxman Valenta powercar than previously expected. The work is currently being undertaken at East Midlands Trains HST depot Neville Hill T&RSMD.
The engine was also fitted to the XPT of New South Wales, which was based on the HST power car design. 18 power car units were ordered,  and built in Australia, by Commonwealth engineering Granville. All 18 XP classed units are in service Like the HST, these power cars have since been re-engined with the VP185.
- Roger Ford (1988). HSTs at Work. Ian Allan.
- The Future of the Diesel Engine. Rail Safety & Standards Board.
- "Fitting the MTU power unit into the HSTs". RailwayPeople.com. 15 August 2008. Retrieved 2010-02-27.
- Hollingsworth, Brian; Cook, Arthur (2000). "XPT Eight-car train". Modern Locomotives. p. 180. ISBN 0-86288-351-2.