Identifying Paxman Diesel Engine Types

The different types of Paxman diesel engines are generally identified by a notation system using a sequence of alphanumeric characters, such as 6RPHXL or 16YJCAZ. The codes have not always been used in an entirely consistent manner but the information provided below should be sufficient to identify most post-WW2 types. For further details of a particular engine range see the page Paxman Diesel Engines since 1934. Information on Paxman's early compression ignition engines can be found on the pages Heavy-Fuel-Oil Engines (1927 - on) and Heavy Duty Diesel Engines (1931 - on).

Identifiers consist of up to five parts, starting with a number, followed by a sequence of letters, as described below. The exception is identifiers which start with an 'A', indicating that the engine was constructed with aluminium major components, as in the lightweight A12YHA engine built for the Admiralty. It should be noted that frequently engines are referred to with parts of the identifier omitted, such as those indicating the number of cylinders, the method of aspiration and/or the application.

First Part of Identifier - Number of Cylinders

The figure at the start of the identifier indicates the number of cylinders. Thus a 6RPH is a 6 cylinder RPH engine and a 12VP185 is a 12 cylinder version of the VP185.

Second Part of Identifier - Class of Engine

The first letter, or two letters, or letter and number, of the identifier indicates the class of engine: -
RP (followed by a letter) = Ricardo-Paxman (indirect injection with Ricardo Comet combustion chamber; e.g. RPH).
Y = High Speed, Vee form, Direct Injection. (e.g. YH, YL and YJ)
Y3 = vee form, Mark 3 (as in the case of the Y3J, conceived as the YJ Mark 3).
Z = in-line, horizontal (e.g. ZH).
RP (followed by a number) = Ruston Paxman (e.g. RP200, RP180 and RP160).
VP = Vee form, Paxman (e.g. VP185).

Third Part of Identifier - Cylinder Bore Size

The third part of the identifier indicates the cylinder bore size, as follows:
G = 6" (e.g. YG and YGA).
H = 7" (e.g. RPH, YH and ZH).
J = 7¾" or 197mm. (e.g. YJ and Y3J).
K = 180mm. (e.g. YK a.k.a. RP180 a.k.a. Vectara).
L = 9¾" (e.g. YL).
M = 10½" (e.g. YM).
200 = 200mm (e.g. RP200 a.k.a. Y3J a.k.a. Valenta).
180 = 180mm (e.g. RP180 a.k.a. Vectara).
160 = 160mm (e.g. RP160 a.k.a. SE a.k.a. Vega).
185 = 185mm (e.g. VP185).

Fourth Part of Identifier - Method of Aspiration et al

A = Air cooled (except in the case of the original YHA engines where the letter was a special identification)
B = Turbocharged and intercooled - air to air intercooling.
C = Turbocharged and intercooled - air to water intercooling.
D = Dual Fuel
E = Non-Magnetic
F = Flameproof
G = Gas Engine
J = Turbocharged and intercooled - air to Jacket water intercooling.
S = Mechanically pressure charged (S for Supercharged)
X = Turbocharged (no intercooling)
If there is no B, C, J, S or X in the full identifier, the engine is naturally aspirated.

Fifth Part of Identifier - Duty or Application

No letter = Industrial
A = Admiralty
K = Standard Alternator Set
L = Locomotive, i.e. Rail Traction
M = Marine Propulsion
N = Navvy, i.e. Excavator - as installed in Ruston-Bucyrus excavators.
T = Traction
W = Oil Well Set (for oil well drilling duties)
Z = Marine Auxiliary (typically for on-board electrical power generation)

VP185 Engine Identifiers - 2012 onwards

With effect from 2012 additional identifiers have been introduced for the VP185 engine range.
Immediately after the bore size (185) is a letter S or T indicating the turbocharging arrangement. S indicates a 12-cylinder type with a Single turbocharger housing or 'box'. T indicates Twin boxes on a 12VP185 or Triple boxes on an 18VP185.
The next letter indicates the type of fuel injection system: C indicating Conventional (i.e. mechanical) injection and E indicating Electronic Fuel Injection (EFI).
As before, the final identifier indicates the duty or application, as follows: G = Industrial / Power Generation; L = Locomotive, i.e. Rail Traction; M = Marine Propulsion; V = Fire Pump; Z = Marine Auxiliary (on-board electrical power generation)

Examples of Identifier Interpretation

6RPHXL = 6 cylinder Ricardo-Paxman with indirect injection Comet cylinder heads, 7" bore, turbocharged (but not intercooled) for locomotive (rail traction) duty.

A12YHAZ = Aluminium 12 cylinder Vee form engine with 7" bore, Admiralty specification, for marine auxiliary use.

16YJCAZ = 16 cylinder Vee form, direct injection, with 7¾" bore, turbocharged and intercooled (air to water), Admiralty specification, for marine auxiliary use.

YGA = Vee form, Direct Injection with 6" bore, air-cooled (the 1950s Vega air-cooled engine)

12YLXW = 12 cylinder, Vee form, direct injection, 9¾" bore, turbocharged, for oil well drilling duties.

18Y3JCM = 18 cylinder, Vee form, direct injection Valenta engine - originally conceived as the Mark 3 version of the YJ (Ventura), with 7¾" bore, turbocharged and intercooled (air to water), for marine propulsion duty.

12VP185TEG = 12 cylinder, Vee form, VP185 engine with twin turbocharger boxes and electronic fuel injection for industrial power generation duty.

Page updated: 22 AUG 2012