Document Type: Technical Manual with detailed line drawings.

Scope: available portions of AP 1590B cover Rolls-Royce Merlin model differences and engine timing

Contents include portions of AP 1590B: - Introduction to Volume II, Part 3 (Instructions for Overhaul) - Table of Main Differences in Design of Merlin Engines - Section 2 (Repair and Reconditioning) - Chapter 3 (Piston, Connecting Rods and Crankshaft - Section 2 (Repair and Reconditioning) - Chapter 9 (Miscellaneous Assemblies).

From the Introduction to Part 3: "1. The following text contains instructions which apply to the following marks of Merlin aero-engine-II, III, IV, V, VIII, X, XII, XX, 21, 22, 23, 24, 25, 27, 30, 32, 45, 45М, 46, 47, 50, 50М, 55, 55М, 61, 63, 63А, 64, 66, 67, 70, 71, 72, 73, 76 and 77, and deals with the inspection, servicing and partial overhaul which may be done by squadrons, and the dismantling and assembling, overhaul and (A.L.6) repair which may be done at suitably equipped bases. Most of the text is common to all these marks, but where differences occur they are specifically mentioned. It will be seen from the frontispiece tables that major assemblies may be fitted to several marks, for example, the type of crankcase which housed the drive for the combustion starter and was originally fitted to the Merlin VIII engine has subsequently been fitted to the Merlin XII, 30 and 32 engines for the same purpose; whilst on the Merlin 47 and 61 engines the drive operates a cabin supercharger. Hence it is necessary in the first instance to ascertain which instructions apply to the engines (A.L.6) or units under consideration.

2. In certain instances modifications to various parts or assemblies may have been introduced which make an engine non-standard; or engines under repair may have been fitted with new part which are usually found on later mark engines, which also make the engine non-standard. As stated in the preceding paragraph, care should be taken to ascertain which instructions are applicable.

3. Should any difficulty arise in deciding which types of parts or assemblies are fitted to any particular engine, reference should be made to Volume I or Volume III of the appropriate aero-engine Air Publication. The engine log book should also be consulted, as this will contain a list of the modifications embodied in the engine and will also provide a clue as to the possibility of parts from other engines being fitted during overhauls.

4. The scope and nature of the work which can be done on these engines is determined by the tools provided in the respective kits, details of which are provided in Chapter 1 of Section 1. This section also describes the operations necessary for the dismantling and assembly of the engine to the unit assemblies, the (A.L.6) partial overhaul of the engine including decarbonizing and valve grinding, and the field inspection for damage due to a crash or enemy action. Section 2 describes the complete dismantling of the unit assemblies, repair and reconditioning work of a light nature, and the final rebuilding of the unit assemblies. In addition to the notes given on the examination of components during the various stages of dismantling, close observation must be made of all components for signs of scoring or burning through undue friction, as it often happens that most valuable indications of defects can be obtained when the oil of the loosened surface of the metal is present to indicate them, rather than after the whole has been washed and laid out for examination."