Paxman RZ, RX and RXL Diesel Engines
Technical Specification

This page reproduces the technical specification of the RZ, RX and RXL series of engines, as published in Paxman Publications No 1115 and 1115A, Paxman-Ricardo "Comet" Head Diesel Engine. RZ - RX - RXL Series, which are undated but not earlier than 1936.

Brief overviews of the RZ and RX engine ranges can be found on the page Paxman Diesel Engines since 1934. The RZ, of 6.7/8" bore and 10" stroke, was introduced circa 1935. The RX, of 9½" bore and 12" stroke, was introduced no later than 1937. The RXL was a long stroke (17"), slower running version of the RX.

Abridged Technical Specification

THE MAIN CONSTRUCTION is of cast iron, consisting of a deep bedplate carrying the main bearings, and separate "A" frames which support the cylinder block with high tensile through bolts which are tightened up to an initial degree greater than the tension which can be imposed upon them by the firing loads of the engine. They then absorb the whole of the working load without further extension.

As a result of the cast iron framing being always in compression and not in tension, the greatest rigidity is obtained and the inspection doors can be kept very large without in any way detracting from the strength.

The framework is arranged to permit the removal of the pistons complete with connecting rod through the crankcase doors without disturbing the cylinder heads or other parts of the engine.

CRANKSHAFT is forged in one piece from the highest quality steel of 36/40 tons tensile strength and machined all over. All, bearings are of ample size to ensure long life.

MAIN AND LARGE END BEARINGS have steel shells and are lined under pressure on the working surfaces with finest quality anti-friction metal.

CYLINDER LINERS. The cylinder block is accurately bored by the use of jigs. Separate liners of wear resisting iron machined to close limits and interchangeable are of the wet type. They are inserted from the top of the cylinder block and free to expand at the lower end.

PISTONS are of cast iron or light alloy of patented construction, heat treated and ground, and fitted with pressure and oil control rings.

GUDGEON PINS are of case hardened steel, ground all over and of the fully floating type free to revolve in the piston bosses. The small end bearing bush is carried in the solid eye of the connecting rod, avoiding the use of bolts and is lubricated from the main system.

CONNECTING RODS are high grade heat treated drop forgings of "H" section (except "R.X.L" Series, which is circular section machined all over) machined in jigs ensuring identical dimensions.

CYLINDER HEADS are cast of special steel mixture and fully annealed, machined to limit gauges, and are interchangeable as are also all parts of the valve gear, atomisers, etc. The cylinder heads are of the patented Ricardo "Comet Head" type, spigoted in the top of the liner, being clear of the cylinder block. The cooling water from the liner flows direct to the cylinder head and passes over the whole of the head surface before leaving.

The heads of the "RX" and "RXL" series are fitted with valve inserts with non-pitting seatings thereby greatly extending the life and reducing regrinding to the minimum.

AIR AND EXHAUST MANIFOLDS are bolted to the cylinder heads, and the exhaust manifold, where not water cooled, is so arranged as to relieve the heads of expansion strain.

WATER MANIFOLDS are embodied in the cylinder block, bringing water inlets and outlets to common points.

AIR AND EXHAUST VALVES are made from steel forgings in special heat resisting alloy possessing great resistance to erosion and to wear on the stems, which, combined with adequate lubrication, results in long life. Working faces of the valves are stellited.

STARTING VALVES are fitted to each cylinder of the engine and on opening the master control are automatically operated in the correct sequence by means of an air distributor.

RELIEF VALVES to the cylinder heads, where fitted, are of the spring loaded type, the springs being protected by suitable shields.

CAMSHAFTS AND VALVE OPERATING GEAR. The valves are operated by push rods and hardened rockers, which bear on case-hardened and ground cams on the camshaft. Full pressure lubrication to all parts of valve gear.

CAMSHAFT DRIVE is arranged at the flywheel end of the engine and is by roller chain, the whole drive being entirely enclosed, but fully accessible for inspection, and pressure lubricated. Full provision is made, by a large jockey sprocket running on ball bearings, for the adjustment of the driving chain.

GOVERNOR is of the centrifugal spring loaded enclosed type, continuously lubricated, and permits of close speed control over a wide range. The speed is adjusted by means of a handwheel while the engine is running.

The governor will control the speed of the engine in accordance with the latest requirements of B.S.S. No. 649-1935 with a momentary variation not exceeding 10% and a permanent of 4%.

FUEL PUMPS are of CAV-Bosch type, which ensures extremely accurate metering of the fuel to each cylinder at all loads, resulting in smooth running. CAV-Bosch service facilities available throughout the world are unrivalled.

ATOMISERS are of the self cleaning fully automatic spring loaded pressure operated pintle type. The spray is carefully proportioned to the Patented PAXMAN-RICARDO combustion chamber and the degree of turbulence of the air charge, ensuring excellent combustion, quiet running, and low consumption of fuel and clear exhaust, and excellent overload capacity.

LUBRICATING OIL PUMP is of the valveless gear type with rotors forged solid on their shafts, and pressure lubricated bearings; means are provided for priming the system before running.

LUBRICATING OIL COOLER. Where conditions necessitate a lubricating oil cooler, a separate external cooler of the multi-tubular type is provided.

FLYWHEEL is of the solid disc type with machined rim and coupling faces.

FUEL SERVICE TANK is fitted with duplex strainers and a sludge compartment which can be cleaned out without stopping the engine.

FUEL FILTER is also provided between the service tank and the pumps.

EXHAUST SILENCER of suitable capacity is provided.

AIR RECEIVER for starting purposes is fitted with pressure gauge, valve and inspection handhole. If required one cylinder of the engine can be arranged for re-charging the air receiver.

ACCESSORIES AND SPARES. One tool box, containing spare piston rings, spare valve springs, and spare joints, 1 piston ring band, 1 complete set of spanners and tools, including all special requirements, 1 grinding in tool for valves, 1 standard foundation plan, 1 instruction book.

SPARES. We keep large stores devoted to fully machined and finished standard parts for the engines, and we invite customers to avail themselves of the facilities we can offer of despatch from stock of any necessary spares.

PAINTING. The engine is painted by competent workmen, best materials only being used.

WORKMANSHIP AND MATERIALS. Workmanship throughout is of the highest class and all materials are the best of their kind. All parts are made with the most modern machinery, and extensive use is made of the employment of specially designed jigs, tools and machines, with the result all similar parts are readily interchangeable.

TESTING. All engines are carefully tested before leaving our Works and a certificate of test furnished.

The above specification applies generally to all engines referred to in this publication, but there are of course, minor differences in design of certain parts the mention of which is unnecessary in a brief specification.

Details and specifications are subject to alteration without notice.

The specification pages of publications 1115 and 1115A have a picture of one engine with the caption: '"4 RXL" Type Engine, 230/250 B.H.P. at 428 R.P.M., 240/264 B.H.P. at 450 R.P.M.', and a picture of another with the caption: '"6RX" Type Engine, 336/370 B.H.P. at 600 R.P.M., 425/465 B.H.P. at 750 R.P.M.'


Table of Speeds and Outputs
4 RZ7501251,000170
5 RZ7501601,000210
6 RZ7501901,000250
7 RZ7502201,000295
8 RZ7502501,000335

For Speeds of 1,000 R.P.M., Engines are especially adjusted at the Works.
The Powers given above can be increased by 10% for overload periods not exceeding 1 hour.


Table of Speeds and Outputs
4 RX600224750280
5 RX600280750350
6 RX600336750420
7 RX600390750490
8 RX600450750560
"RXL" Series
4 RXL428230450240
5 RXL428285450300
6 RXL428345450360
7 RXL428400450420
8 RXL428460450480

For Speeds of 750 R.P.M., Engines are especially adjusted at the Works.
The Powers given above can be increased by 10% for overload periods not exceeding 1 hour.

Page updated: 07 JUL 2016