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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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