For the rebuilding of complete engines the crankcase-cylinder block forming the main carcase was mounted on a portable stand, and ten of these stands formed the assembly line (pictured right). The portable stands provided for flexibility in the progress of an engine along the line, according to rebuilding priority. Movement of engines was by a battery electric pallet transporter. From the accumulated stock of components in the repaired detail storage the sub-assemblies were made up and then transferred to the assembly storage racks situated at the end of each line in readiness for final assembly. A continuous bench at the side of the track was used to keep equipment off the floor during assembly. For the final assembly a series of portable erecting stands were arranged across the ends of the eight belt lines. Erection was performed in four stages. Each stand and unit were moved to the end of each pair of belt lines for the respective sub-assemblies to be erected. Patrol inspectors on the line ensured that the required high standard of cleanliness and workmanship were maintained, and that the complete build is to specification requirements.
At the completion of the rebuild the engine, fitted with auxiliaries, was run-in and load tested on a Heenan & Froude type DPY5 hydraulic dynamometer.
This was suitable for testing engines up to 640hp. Driving through the brake was a 35 h.p. 300-800rpm variable-speed electric motor (it can be seen on the right of the control panel). This was used to motor the engine for a short period to remove initial stiffness and circulate the oil. Following a run of 30 min. at no load the engine was run for 2 ½ hr. with progressive load increments at speeds between 1,000 and 1,800 r.p.m. This was followed by a series of tests over the same speed range at the maximum rated output for each speed. Fuel consumption was checked with a Flowrater meter, measuring the rate of fuel flow in c.c. per sec. The test bed was equipped with a 400-gal. fuel tank, and a 100-gal. cooling-water header tank fitted with a Drayton automatic temperature regulator. Lifting the engine on and off the test bed and on to the transporter vehicle after painting was by a 1 ton capacity overhead travelling crane. This single test bed was soon inadequate to deal with the flow of engines then being handled by Derby, and by 1959 additional test beds were being installed in an adjacent building. The first of these is pictured in the final image.
In addition to the overhaul and rebuild of complete engines, an increasing amount of component repair work was carried out for other diesel depots in the London Midland Region. A stock of reconditioned components was held in store ready for immediate issue as replacements when defective parts are received. The defective parts were then reconditioned and returned to store, or if not repairable new parts are issued as stores replacements.