Engine Rebuilding to Plan
Page 72
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ONE of , the modern' problems in the complete rebuilding of oil engines is that their life has become so greatly extended that' few operators find it economic to keep men and expensive machines available for this work. To a lesser extent this also applies to rebuilders
in a smaller way of business. , Some years ago the A.E.C. concern stepped into this widening breach with a scheme for changing completely overhauled units for those of all types of
operator. Now the increasing demand of this valuable service has necessitated the conttruetion of a new 'shop at Southall 'rOvering some 30,000 sq. ft. and fully equipped with the latest -and highly expensive. plant. The .through-flow of engines'is already 30-3.5 per week, but the capacity is 50 on normal' work or 100 with also a night shift.
In general the 'engines lose their
duality, although a few, operators. still
• demand the return of their own units, although this may upset the flow to some extent. Basic charges are made for engines of various models. They vary from £205 to £285 for current models, the price also being influenced -by particular equipment and the supply of really expensive new parts such as crankcase, cylinder block or crankshaft, which, however, are seldom required.
There is no oversaing of bores and pistons, every exchange unit having new liners, pistons and rings, and main and big-end bearings, whilst crankshafts are reground to any of four standards in 20-thou. steps. • The basic charge also does not apply to certain older engines, although these are accepted for overhaul. They often require special treatment such as lineboring of bearings where the crankcases are split at the mains and are not so rigid as•the modern monobIoe type. Most important of all is that every engine is given a year's guarantee, thus showing it to be considered as completely sound as a new one. Each is dynamometer tested for a whole day, working up from light load to full -power, and all fuel pumps are calibrated on Hartridge test benches.
The following is the rebuilding process• in brief:— Engines on arrival receive a first wash in a bath of Solvex crystals, and after dismantling the parts are soaked in liquid Solvex. Carbon is removed by fettling, wire• brushing and the use of Ardrox. Wet liners are left in, but the dry type pressedout ready for water testing the cylinders. In a few cases crankshafts have to be straightened in a 'press, but this is exceptional. Where line-boring is done the bearings are lead-flashed electrically in the main production factory.
Pressed-in cylinder liners are honed to finished size. Wet liners must project 1-4 thou. for finishing and are sprayed with a special aluminium oxide material to obviate cavitation erosion. Valve seats
are always replaced and the new valves have Stellited faces and chromium plated stems. Valve rockers are trued, by grinding. Welding is eschewed, cracked parts being renewed.
'A new process is the double-end boring of connecting rods, and new bolts are always fitted. Many hundreds ofconnecting ,rods are provided as spares for users and repairers who have insufficient facilities for this work. On many modern types precision bearings are used and boring is not required.
Stores of new parts and supplies -of those reconditioned meet at what known as the "nerve centre," and here they are, marshalled in completekits ready for assembly by -individual -operators—so that responsibility can be placed-Each finished engine is coated with rubberized paint.
Full justice cannot be given here to many other interesting matters, such as the crack-testing of crankshafts, the meticulous inspection, the overhead taliways and the battery-electrictruck–for transporting units to the -test house.