Yeading - Motor Transport Repair Depot


The Post Office Electrical Engineers’ Journal
Vol. 42 - April, 1949
U.D.C. 629.113.004.67


Yeading Central Motor Transport Repair Depot
Part I
By A. G. McDonald

The Post Office has recently opened an extensive repair centre at Yeading, near Greenford, Middlesex, for the overhaul of motor transport vehicles, units and components, on a “factory” basis. This article describes the circumstances that led up to its inception, how it fits into the existing nation-wide scheme of repair for motor transport, its functions, and also details of its layout and equipment.


Introduction
The Post Office fleet to-day consists of some 25,750 vehicles and is still rapidly increasing in number.  Although a high proportion of these vehicles is of Morris (Morris Motors and Morris Commercial) manufacture, owing to the sudden need in 1946 to obtain vehicles for the Engineering fleet expansion and also because of the inception of the Engineering Department's Road Haulage Scheme 1, the Post Office was forced to take over surplus Service vehicles and in consequence the fleet now contains practically every known make.  Amongst the petrol-engined vehicles are such makes as Albion, Austin, Karrier, Leyland, Fordson, Bedford, Bedford-Scammell and Crossley.  The oil-engine makes include Maudslay, A.E.C., Leyland, Foden, Albion and Scammell (Gardner engines predominate).  In addition to this commercial vehicle fleet there are a considerable number of passenger cars and also a few omnibuses.  The number of motor cycles is round about 600. It may be of interest to note that the number of vehicle types listed for costing purposes is 95.

In the Morris Motors range the principal chassis types are the “Z'' (used on Engineering Minor and Postal 50 cu. ft. vans - R.A.C. rating 8.05 h.p.) and the “Y'' (used on 8-cwt. Engineering and 100 cu. ft.  Postal vans - R.A.C. rating 11.98 h.p.).  In the Morris Commercial range the chassis used are the "LC'' (for Postal 240 cu. ft. and Engineering 1-ton Utility and 1-ton Stores Carrying vehicles - R.A.C. rating 15.9 h.p.), and the “CV” chassis (for 360 cu. ft. Postal and Engineering 30-cwt.  Utility and Stores Carrying and Engineering Test vehicles - R.A.C. rating 24.8 h.p.).  There are also two other makes which are held in quite large numbers, the Albion (30-cwt. B.118 engined chassis - R.A.C. rating 19.6) and Austin (2-ton chassis with engine of 26.9 h.p. - R.A.C. rating).

Necessity to Replan Motor Transport Repair Organisation
Although to a very great extent overhauls and repaints as well as day-to-day maintenance have been carried out in the great majority of the 350 Regional workshops, a degree of central working had been developed in each Region in the reboring of engines, replating of batteries, overhaul of electrical components and overhaul of Engineering lorries.  This work was allocated to certain of the Regional workshops because it was not practicable to supply costly equipment such as boring bars to all of the workshops, while batteries and electrical components were segregated because of the requirements of specialist staff and of special equipment and accommodation.  This measure of centralised repair would, but for the war, have been developed to a far greater extent.  At the same time another factor made it very necessary to give urgent consideration to the setting up of Central Repair Depots. In 1939, the fleet totalled approximately 17,500 vehicles.  To-day, it is almost 50 per cent, greater in number and, consequently, in
maintenance requirements.  During that period of growth, as a result of the almost total ban on new buildings from 1938 onwards, the additional workshop accommodation provided to meet this growth has been practically negligible. Consequently, all workshops to-day are carrying on under very grave handicaps.  Apart from the limitation of workshop space, an increasing number of vehicles have to remain overnight in the open, which results in extra maintenance attention being necessary.

It has therefore become imperative to replan the complete Motor Transport repair structure to avoid a breakdown.  The existing workshop buildings are sited mainly in built-up areas on relatively costly sites where their location and size is dictated by the requirements of the operating centre of the user.  For Postal vehicles, in order to avoid very heavy off-centre operating costs, they are usually sited as near as possible to the Sorting Office, which is in turn generally sited near the Railway Station, while for the Engineering Department's Section Stocks and Garages, although these are farther out and not necessarily in the centre of towns or cities, they are in the main in built-up areas where no extension is possible.  Consequently, as it is  impracticable to increase the size of the present workshops the logical solution to give relief is to leave these existing workshops to carry out day-to-day maintenance work and to set up new workshops, not necessarily in the business centres of population, to carry out that work which can most conveniently be divorced from running repairs.  The location of these secondary shops is not critical and less expensive sites are suitable.  This policy enables the user's day-to-day maintenance requirements to be fully met by staff stationed with the operating fleet and at the same time permits overhaul staff to work without the distraction of attention to faults.

When the overhaul requirements were analysed in greater detail, paying special regard to the distances that some vehicles would have to go and also to the high cost of some of the machine tools and specialised equipment needed, it was realised that it would be desirable to divide the overhaul responsibilities still further.  Such work as chassis stripping and repaints, coupled with unit exchanges, could quite well be carried out economically in selected shops in each Region and consideration of the problems of delivery and collection of vehicles and components suggests that the economic radius of operation of these workshops should be in the neighbourhood of 40 to 50 miles.  Usually each Region will require two or more of this
type of overhaul workshop, giving a total for the country of approximately 20.

Machine tools and specialised equipment for the overhaul and testing of engine and other major components are very costly and this work must be
done in bulk to cover the very considerable overhead charges.  These factors necessitate the concentration of such repetition work as engine overhauls, including crankshaft regrinding, and unit and component overhauls in a limited number of National Repair Depots planned on factory lines.  The organisation now being planned for the country as a whole is:-

1st-Line Workshops [Regional).  Day-to-day maintenance, valeting, decarbonising, top and bottom overhauls, minor accident repairs, preventive maintenance to body and chassis, tuning, brake and clutch adjustments.

2nd-Line Workshops [Regional).  In these workshops complete vehicle strip-down and rebuilds would be performed, utilising reconditioned units and components sent forward from the 3rd line workshop.  The operations performed would include engine, gearbox, front and rear axle exchanges, component exchanges, body dismantling, chassis stripping and rebuilding, brake shoe relining, brake drum turning, clutch relining, major accident repairs, body repaints and semi-major body repairs.  Each 2nd-line workshop will act as a parent to a group of lst-line workshops.

3rd-line Workshops [National).  Overhaul on a "factory” basis of engines, gear boxes, front and rear axles, electrical components and accessories
received from 1st- and 2nd-line workshops.  Engine running-in and dynamometer testing.  Reconditioning of batteries. In addition, the 2nd-line workshop functions will be effected in respect of vehicles within a radius of 40 to 50 miles.  Further, the staff, accommodation and equipment available render the 3rd-line workshop eminently suitable for building prototype bodies and carrying out test work required for development, time studies, checking advertisers’ claims for new equipment and accessories and performing work necessary to assist the Motor Transport Branch purchasing section.

In considering how many 3rd-line workshops would be necessary to cover the country it was decided that initially two Central Repair Depots would be required, one in the South of England and the other in the North, which would permit of covering practically the whole of England and Wales and parts of Scotland until such time as the density of vehicles called for additional 3rd-line workshops.  Accommodation has not yet been finally secured for the workshop in the North of England, but after many disappointments suitable premises are under consideration and strenuous efforts are being made to secure them.

For the Central Repair Depot in the South, an opportunity came of taking over suitable premises in a very convenient and economic operating and
distributing centre at Yeading, near Greenford, Middlesex.

The Yeading Central Repair Depot
The premises taken over form a self-contained section of what was, during the 1939-45 war, a Royal Ordnance Filling Factory.  The buildings and layout are typical of many similar factories which sprang up in various parts of the country during the war for the manufacture of armaments, and comprise single storey, modern, factory-type buildings of various sizes and heights, administrative office blocks, first aid centre, fire station, etc., the whole being set out with adequate approaches and service roads and the site of 120 acres bounded by wire fencing. The workshop accommodation consists of one main factory and one smaller adjacent workshop which is eminently suitable for a paint shopwork which is preferably segregated from other workshop processes.  In all, some 247,000 sq. ft. of workshop and office floor space is available.

All buildings are steam heated, supplied from a battery of high pressure steam boilers which are fired by mechanical stokers having electrically driven
chain grates fed by hoppers. Distribution is by overhead piping suspended on gantries.  The heating within the main workshops is by fan unit heaters.
It is well known that this type of element gives space heating in winter and improves ventilation in both winter and summer.  Another factor that was of
considerable help in enabling a substantial amount of machinery to be installed speedily was the presence of electricity supply mains adequate for a very heavy load.



Fig. 1 - Layout of Yeading Repair Depot

The immediate objective in setting up this Central Repair Depot was to deal primarily with the vehicles of the London and Home Counties Regions but it is the intention, as staff becomes available, to extend unit and component replacement services to the South West, Welsh and Border Counties and Midland Regions, thus linking up with the service area of the Northern Central Repair Depot. Production of reconditioned engines is already sufficient to cover the London and Home Counties fleets and in addition, urgent relief has been given when emergencies have arisen in other parts of the country.  This necessitates a minimum output of 60 reconditioned engines per week of the usual Departmental types in addition to a number of types less commonly used.  Another objective aimed at in equipping the Depot was that it should be, as far as possible, self-supporting, and not have to rely on outside contractors for specialist repairs such as crankshaft grinding, welding of cylinder blocks, etc.  During the recent war it was found impracticable to secure satisfactory services outside for this class of work as the time factor was in most cases extremely unsatisfactory and the charges
high, even making allowances for all the circumstances.

Hence the staff of the Depot comprise a great many other grades of craftsmen and tradesmen apart from Motor Mechanic.  Included are turners, milling machinists, precision grinders, crankshaft grinders, tool room fitters, production inspection staff, sheet metal workers, specialist welders, automobile electricians, body builders, wood working machinists and coach painters.

In laying out and organising the work within the Depot (see Fig. 1), a primary objective was to ensure that the work circulated within the building on a flow system in order to reduce time in transit between successive operations.  Even allowing for the fact that the buildings were not planned for the purpose and had to be occupied in two stages, this objective has very largely been achieved although some replanning and greater use of mechanical handling devices is regarded as desirable and is in hand.

Preliminary Treatment of Vehicles
The vehicles on arrival have a thorough external wash and are delivered to the stripping bay where the first operation is to remove engine and gear box.
Next the body is removed and placed on one side to await inspection before transfer to the body line. The front and rear axles are then removed from the chassis complete with springs and steering, leaving the chassis frame ready for cleaning and reconditioning.

This sequence refers to light and medium vehicles where the individual chassis and body can readily be shifted by electrically driven trolleys. For heavier vehicles, e.g. diesel driven, the vehicles are cleaned in the stripping bay and then the complete vehicle is transferred to the heavy vehicle body shop where the body is raised from the chassis and left suspended on chassis stands. The chassis is next removed to the heavy vehicle chassis line where the engines, gearbox and front and back axles are stripped out and brought back to the stripping bay for further dismantling followed by degreasing.

It should be mentioned that the original components of a heavy vehicle will, after reconditioning, come together again during assembly but in general the smaller vehicles are assembled from a number of reconditioned units irrespective of their origin.  This policy is followed also in respect of the actual components of the smaller engines with one exception the engine block and camshaft are kept together as there is no way of taking up wear in the bearing located in the engine block other than by metallic deposition on the camshaft.

Fig 2 - Degreasing bay

Degreasing and Cleansing
Various methods of degreasing and cleansing are employed.  No one method is suitable for the whole range of operations but each of the methods adopted has been selected as being the most suitable and economical for a particular operation.

Trichlorethylene Vapour
Used for heavily grease-laden parts not having a carbon deposit and also for non-ferrous parts which are likely to be attacked by other processes.  This method is very successful but it is expensive and somewhat unpleasant to operate.

Hot Caustic
This method is used for hard carbon deposits on cylinder blocks and cylinder heads. It is not suitable for aluminium components.  After treatment in the hot caustic tank, parts are rinsed off in a second tank containing hot water.

High Pressure Steam
Useful for removing exterior dirt on larger components such as chassis frames and axles, and when used in conjunction with a suitable cleansing agent can be employed for paint stripping.

High Pressure Paraffin Wash
Used mainly for degreasing ball and roller bearings which are afterwards dried off by an air stream and then immersed in a light oil.

The various components, after degreasing and drying, are blown with compressed air to remove all surface dust; cylinder blocks and cylinder heads are wire-brushed to remove all trace of carbon deposit.  All the components then pass in for inspection where they are graded broadly into:-

(1) Parts suitable for further use without treatment.

(2) Parts needing reconditioning.

(3) Parts treated as scrap.

Those parts in category (2) are sent in batches to the various repair sections, and after reconditioning are again inspected and returned to stores where, together with parts in category (1) plus any required new parts, they are made up into kits ready for assembly.  The workshop is well equipped both with ordinary machine tools such as milling and drilling machines, lathes, surface grinders, etc., and the specialist machinery which has been developed for the motor industry.  In the latter category are such items as crankshaft  grinders, cylinder boring machines, in-line bearing
boring machines, etc.

Repair and Reconditioning of Engine Components
The primary reason for overhauling an engine is almost invariably wear in the cylinder bores, and engines are selected for overhaul when bore wear is .010in. to .015in. according to the size of engine.  The wear results in a falling off in performance and excessive consumption of lubricating oil; in consequence, the user complains of the engine fuming. A contributory cause of fuming is compression piston ring wear or breakage.

The conditions of service for the Post Office motor vehicle fleet are very severe as compared with those of normal trade or private vehicles. Owing to the frequent starting and stopping necessary and the continual operation at low temperatures, bore wear is heavy. An additional adverse factor in accelerating wear is that to cover day and night services many Postal vehicles are driven by relays of drivers.

Cylinder Blocks
For light vans of capacity 5-8 cwt. 20,000 miles is a reasonable bore life between overhauls, while for vehicles used mainly in towns, it may fall to
15,000 miles. For vans used on rural services where the runs are long and stops fewer, lives up to 25,000 miles are obtained. When the engine is dismantled, primarily on account of bore wear, it is found that other parts of the engine need attention.

On 1-ton vans, the average bore life may be taken to be of the order of 25,000 to 30,000 miles but quite a number are found to last up to 50,000 miles.  Bore wear is of the order of .001in. in 2,000 miles.

For 30-cwt. to 2-ton vehicles the record of bore wear is considerably better and lives of 70,000 miles are not uncommon, although it may fall to 30,000 miles for vans used exclusively on short runs.  A number of blocks passing through the workshop after a life of 30,000 miles showed a bore wear of .008in. and the bore wear of this type may be roughly stated as .001in. in 4,000 miles.

About 2 per cent, of the cylinder blocks going through the workshop are found to be cracked either as the result of old frost damage or strain in use.  The cracked blocks are welded and in this connection it might be mentioned that welding of cast-iron calls for a high degree of skill and knowledge.

The region of greatest wear in a bore is on the thrust side immediately below the top of travel of the top compression ring.  Cylinder blocks are reconditioned by boring out to .020in., .030in. or .040in. over standard size depending either on the condition or whether the bore had already been bored out at a previous overhaul.  If the bore does not fall within these limits or cannot be cleaned out within the .040in. oversize on the smaller engines or .050in. to .060in. on the larger engines, the bore is machined out to a larger diameter and a liner inserted.  The cylinder block is bored to such a
diameter that an interference fit is obtained when the liner is driven into position by a hydraulic press.  The liner is then bored to size to take standard pistons.

It is interesting to note that in general, cylinder bore wear is about one-third less over the same mileages for blocks fitted with liners as compared with the original blocks.

Valve Inserts
In hot running, high
efficiency engines, severe demands are made on the valve gear and valve seatings.  When a block is due for rebore it is frequently found that most of the valves are pocketed and in need of reconditioning.  This operation is carried out by boring out the seating to take a new cylindrical insert which is pressed home; a new seating is then ground on the insert to provide line contact.  When blocks are found to be cracked round the exhaust valve seats, this trouble can usually be overcome by inserting a new valve seat.

The cylinder block face is also examined and if the irregularities in the surface exceed a permissible tolerance of .008in., the block is surface ground to ensure a gas-tight joint.

The final operation on the cylinder block is to remetal the main bearings after which these bearings are line-bored to dimensions determined by the diameter of the corresponding journals of the crankshaft to be fitted to that particular engine.

Crankshafts
Crankshaft journal wear does not take place evenly; when examined practically all crankshafts are found to have some degree of ovality.  In addition, the majority of crankshafts are found to have a certain amount of scoring, probably due to abrasive material which gets in the oil stream.  Consequently, it is the practice to regrind all crankshafts passing through the workshop.  This work is carried out on a battery of crankshaft grinders, which are very high-grade machines, and the Post Office was fortunate in being able to acquire from Government surplus disposal depots such excellent machines as Landis, Norton and Van Norman, although practically all of them required a certain amount of reconditioning.  In addition, jigs had to be made to allow the offset journals to be ground.


Fig. 3 Crankshaft Grinders

Crankshaft grinders (see Fig. 3) are usually worked in pairs, one machine grinding the main journals while a second machine grinds the offset journals.  This results in a substantial saving of time as it is not necessary to alter the setting of the machine except at the end of a batch.  One machine acquired was designed for what is known as plunge grinding, which process simply explained means employing a grinding machine with its face trued up to the exact contour of the bearing journal.  The machine automatically takes its cut to a pre-determined depth and then releases and withdraws the wheel carriage in readiness to repeat the process on another journal. The operator, therefore, has only to move the machine to the next grinding position.  The other machines in use have been modified to employ a somewhat similar plunge system but on these the operator has to feed the grinding wheel in by hand to a depth indicated by "Zero” position on a Mercer dial type gauge.

The majority of crankshafts are found to clean up at first overhaul to .005in. or .010in. undersize.  At subsequent overhauls regrinding in stages of .005in. up to a maximum undersize of .040in. for small engines and for the larger crankshafts up to .060in. under size is usual.  Thus, one crankshaft will last at least five engine overhauls after which a new crankshaft is required. The number of crankshafts breaking in service is very small indeed.

Building up of journals either by electrolytic deposition or by metallisation, i.e. metal sprayed on in a molten condition after the journal face has been roughened has not yet been undertaken, but is under consideration.

Connecting Rods
These are checked for truth and size of bearing aperture and then remetalled.  One method is to metal the bearing alloy into the rod itself and the success of this method is probably due to the satisfactory heat transference which results from the intimate contact between the bearing metal and the main material of the connecting rod.

The connecting rod big-ends are bored out to size to suit the crankshaft supplied for a particular engine.  The diametrical clearance between the crankshaft journal and the bearing surface is normally .0015in. while the permissible end play is of the order of .005 in. to .006in.

Pistons
New pistons complete with rings and gudgeon pins are usually fitted at each overhaul, but a measure of recovery is carried out by turning down to normal size used oversize pistons.  This work is carried out on a special machine and at the same time the piston lands are cleaned up to take new piston rings.

General Machining
As mentioned earlier in this article, as well as the specialist machines, a considerable number of general machine tools are used mainly for recovery purposes to take out scoring, indentation or warping.  Cylinder head warping occurs either by reason of normal working stresses or by excessive unbalanced bolting down.  Where the warping exceeds a permissible tolerance of .008in. the cylinder heads are refaced on a vertical milling machine using an inserted tooth cutter.  Jigs have been made for each of the standard makes overhauled and this operation can be carried out quite quickly and shows a big saving over contract prices previously paid for this work. Fig. 4 shows a view of part of the general machine shop.

Surface grinders have proved most valuable especially in dealing with hardened parts where ordinary  machining is not possible. Truing-up of fly wheel faces, clutch pressure plates, clutch thrusts, etc., also provide ample scope for the use of these machines.  Formerly many such items were scrapped because facilities for reconditioning were not available.  Similarly, tappet heads and tappets are ground to give a true surface and in all the examples quoted, a large number of items are ground at one operation, special jigs made in the Central Repair Depot being employed.  On recovery work of this nature a clear-cut saving is evident.

One of the hardest worked machine tools in the depot is the radial drill.  In the process of overhaul it is found that tapped holes in castings are prone to damage either by threads being stripped or by past efforts in the field to remove broken studs.  This damage is made good by filling up the hole by welding, or by drilling out to an oversize and inserting a metal blank which in turn has to be drilled and tapped.  This operation calls for precision as correct positioning of holes is essential to register with other components.

The lathes in the general machine shop are used for production of a variety of bushes and pins and for the production of some of the simpler parts which are in short supply.  It becomes a serious matter when the whole production of a workshop is jeopardised by the absence of essential spares, and the ability to turn out a number of these to bridge the gap is obviously of great value.

Brake drum turning to remove scoring is carried out on a special brake drum turning machine.  The friction surface of the brake drum becomes work-hardened and highly polished with deep scoring and to cut into this surface it is necessary to use tools having cutting tips of tungsten carbide or similar alloy.

Fig. 4 - General Machine Shop

Tool Shop
As the bulk of engines dealt with are, fortunately, of a limited number of types, repair and reconditioning in batches has been made the standard system.  To do this economically calls for production of special jigs and fixtures to make the operation as far as possible approximate to mass production methods.  This was visualised right from the inception of the workshop and a very fully-equipped tool room was provided.  The equipment includes high-grade-lathes, universal miller, shaping machine, cutter grinder, "do-all” metal band saw and a number of smaller precision machine tools as well as a Vickers Hardness machine.  The tool room, as is usual, is partitioned off from the main machine shop so that the machine tools provided can be kept for high-grade work only and not for heavier production turning.

Inspection
All components, after reconditioning and before issue on the assembly lines, are subjected to close scrutiny by an independent inspection section.  This group is well equipped with comparators, hardness testing machines, spring testing and measuring machines, together with all the necessary micrometers and fixed gauges.  A crack detector is used for examination of parts heavily stressed in use, such as crankshafts, steering arms and stub axles.

Assembly of Engines and Gearboxes
The assembly of components into engine and gearbox units is dealt with broadly by two methods.

For light engines which form the bulk of requirements, assembly is on the line system, that is, the complete engine is assembled in stages as it proceeds
through various hands on the line.  A separate line is in use for each of the main types.

The assembly starts with a complete kit of components necessary to build the engine and this is prepared in advance of requirements by the "Initial Inspection and Make-up Section".  The work benches adjacent to the line (see Fig. 5) are equipped only with such tools as are necessary at each stage of the work and the work is facilitated as far as possible by the use of high-grade ring and socket spanners, torque spanners, and electric nut runners.  Specially designed wrenches and fixtures have been provided where necessary to speed up the work.

Fig. 5 - Engine Assembly Line

The heavier engines such as Gardner Diesels are assembled by individual mechanics and do not pass through several hands.  The “initial kit" system applies, but these types retain their identity so far as components are concerned and as distinct from the main types where parts are, in general, freely interchanged.

Completed engines all pass through some form of power testing and here again the light types are specially treated by being first run-in in tandem on suitably designed cradles. One engine under its own power drives by means of a connecting shaft a similar engine not under power.  After a running-in period of one to two hours according to how the engines behave under test, the driven engine is powered and in turn provides the means of running-in a further engine.  A proportion of the light engines are finally tested fully for power and consumption on a Heenan Froude (DPX 2 model) dynamometer, to ensure that the results are consistent with the maker's design and that the repair tolerances, etc., are acceptable and unlikely to cause trouble in service.

The heavier type engines are not given this initial tandem running but are brought up slowly to full power on test benches made by Messrs. Bennett Feregan.  These dynamometers (Fig. 6) absorb the engine power hydraulically and give direct readings of torque.  During the course of testing an analysis of exhaust gases is made to determine the suitability of the carburettor settings.  A cathode ray oscilloscope is used to provide visual evidence of the efficiency of the whole of the ignition system.

Fig. 6 - Bennett Feregan Dynamometer

Carburettors and Diesel Fuel Pumps
It will be appreciated that if the best results are to be obtained from an overhauled engine it is important that the carburettor should be subjected to close examination and repair.  There is no doubt that this engine component is still very largely a specialist job and the best settings can only be obtained by testing in conjunction with its individual engine.  A small shop has been set up apart from the main workshop for carburettor repairs and is equipped with all the necessary small tools and testing equipment proper to this class of work.

A similar workshop has also been set up to deal with diesel fuel pumps and injectors.  The requirements of this work are exacting as the atmosphere must be entirely dust free and to this end the workshop is sealed and provided with a small air conditioning plant.  Floors and walls have to be given anti-dust treatment.  The equipment of this workshop includes a Hartridge test bench which is used for calibrating, phasing and testing of fuel oil pumps, while injectors, after servicing, are tested in a sprayer test cabinet.

Heavy oil engines (diesel) are finding a growing use in the departmental fleet of heavy vehicles and considerable additions of this type have been made by taking over vehicles from the Government Surplus Depots.  In recruiting staff for the Yeading workshop particular care was taken to engage a number of men with wide diesel engine experience both as regards the actual fitting work and testing.  This precaution has enabled all classes of this type of engine to be dealt with fully and has provided very satisfactory results.

It might be mentioned that diesel-engined stand-by power units were also acquired from Surplus Depots to assist in the event of electricity load shedding and these were overhauled at Yeading and installed both at Yeading and in the Factories Department, Perivale.

Repair of Electrical Units
Electrical units, in common with the general system employed in the workshop, are repaired in batches.  As far as possible staff are employed for lengthy periods on the repetitive overhaul of one type of electrical component and thus become very expert in the course of time.  A special bench is set up for each piece of equipment to facilitate the layout of tools, testing equipment and spares.  The general layout is illustrated in Fig. 7. The aid of the machine shop is enlisted in cleaning up the contact surface of the many types of commutator used in dynamos and starter motors.

The number of items dealt with in the electrical section is fairly high, possibly because electrical equipment in general is not of such robust design as the mechanical parts of a vehicle.  Another factor is that this equipment suffers two types of damage, i.e. mechanical and electrical, and electrical faults frequently result from mechanical failures.  Examination of the components passing through the workshop for repair shows that they exhibit the following characteristic defects.

Trafficators suffer mainly mechanical damage due to the driver or passenger colliding with them while they are in the "indicating" position.  This particular type of damage is due to the fact that many of them after a time fail to be self-restoring. It is significant that a leading manufacturer has recently produced a trafficator for commercial vehicles having an articulated arm.  One other fault occasionally experienced is that of an electrical burn-out caused by failure of the arm to rise when switched on, due to jamming in the casing.


Windscreen Wipers
These fail mainly as a result of commutator and brush wear with consequent choking by dust, causing bad brush contacts.  Failure can also be caused by overloading consequent on continuous running, particularly if the screen becomes dry.

Fig. 7 - Electrical Component Repair Section

Instruments
Ammeters frequently bum out, generally because of accidental short-circuits.

Petrol Gauge
Failures are usually due to the breakdown of the potentiometer coil in the tank or to puncture of the float.

Fuel Pumps
Breakdown occurs either in diaphragm or contact.  Failure of the diaphragm from fatigue throws an overload on the windings and this in turn leads to burning of contacts.  The diaphragm life is much influenced by the ambient temperature.

Regulators
The introduction of this item in place of the simpler cut-out mechanism has given an improved performance but results in more repair work because of its comparative complexity.  Incorrect wiring after clearance of a fault can result in the burn-out of contacts.  Another type of fault occurs if the regulator is adjusted to compensate for high resistance in the external wiring, this leading to overheating with the possibility of subsequent burn-out.

Dynamos
Electrical faults are not often experienced, the primary cause of breakdown being mechanical failure.  Wear on pulley-driven armature shafts results if the drive pulley runs eccentrically on the shaft thus setting up undue strain and fatigue.  Excessive fan belt tightening has the effect of putting undue pressure on the bearing causing the armature to receive damage by coming into contact with the dynamo stator.

Starters
Some starters exhibit considerable commutator wear, but on examination brush spring pressures are found to be normal and commutation correct.  Electrical breakdown follows because of the extreme effort required when starting a cold engine.

Batteries
A well-equipped battery shop is used for conditioning and replating the batteries, and handles all types of battery in use.  Complete replatals and the manufacture of such items as connectors are undertaken.  Initial charging of the completed battery is by the constant potential method carried out in a suitably designed enclosure.  A number of rapid chargers are employed for boosting batteries of vehicles in transit; in these the charging current, which may amount to 90 amps., is controlled by a thermostat placed in the electrolyte and a 120 amp. battery can be fully charged within one hour.

The main value of this shop lies not so much in the immediate saving, which is quite considerable, but in the ability to keep the fleet supplied with batteries when trade sources of new batteries have dried up.  This has happened on many occasions.

Bodybuilding Workshop
In contrast to the mechanical work of reconditioning engines in which a measure of repetition is possible, thus permitting a regular routine to be adhered to, bodywork has proved much more difficult to organise.  The wide variety of bodies and the multiplicity of individual jobs to be carried out has called for very considerable detailed planning in order to organise the work properly.  For the mass-produced types, the solution is felt to lie in a very much increased use of jigs.  For example, when the work was started it was the practice, if a body was distorted, either to select a door which could be fitted to it, or alternatively to modify the door.  Operations such as these take a considerable amount of time and it is better, by using jigs, to bring the vehicle body and doors back to standard dimensions.  Again, this method allows damaged or rusted parts of the body to be cut out and fresh parts welded in with comparative ease.

The mass-produced pressed steel body is in use on most of the standard cars and light vans produced by the motor industry to-day.  It undoubtedly provides a method of construction economical in manpower which is a great asset to the manufacturer, for the maintenance engineer, however, this means a constant battle against corrosion.  Vehicles now leaving the manufacturers works are given coats of aluminium paint in an effort to keep corrosion at bay, and most makers are introducing methods of rust-proofing for both body and chassis.

Fig. 8 - Light Van Body Shop

A further factor is that postal vehicles back in and out of loading bays several times per day, and it is inevitable that they sometimes sustain body damage during such operations.

These factors make it difficult to achieve the desired result of the flow of bodies being equal to the flow of engines, but the position is now improving.  For the larger and more expensive vehicles the problem is not so difficult and very satisfactory production has been achieved.  The specialist coachwork calls for individual treatment, but as compared with charges for similar operations carried out in the past, and which are still being performed in the country as a whole, the central workshop will undoubtedly show large savings.  The inception of the National Road Haulage Scheme would have been well-nigh impossible without the facilities afforded by the Yeading workshop.  Already nearly 200 heavy-load carriers, including many 12-ton oil-engined vehicles, have passed through this workshop and frequently the bodies had to be practically rebuilt.  Another formidable task was to reduce the width of many heavy vehicles from the Service 8 ft. to the maximum legal width of 7 ft. 6 in.  This meant cutting the cab in halves and rebuilding; the body bearers had to be reduced and the sides repositioned.

Other interesting jobs which have passed through the body shop have been the production at short notice of a Mobile Post Office, the conversion of R.A.F. radar trailers to take mobile automatic exchange equipment and the overhaul of a “Jeep” and “ Dukw” for Criggion radio station.

A further activity of the body shop is the production of prototype bodies prior to bulk manufacture.  Previously it has been necessary for this work to be carried out at manufacturers’ works - a slow and costly process.  A recent example of prototype body building has been the production of the proposed 2-ton utility van designed to supersede the present 30-cwt. vehicle used by
main line gangs. 

 
 
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Last revised: April 02, 2019

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