Southern Electric Group 4Cor unit 3142 Preservation Report 1

Overhauling a 1938 Power Bogie

In the summer of 1996 we asked our landlords at St Leonards Depot, St Leonards Railway Engineering Limited (SLREL), to move power car 11187 under the crane so that we could remove the power bogie for overhaul. SLREL generously agreed to this so in August 1996, 11187 was shunted underneath the 25 ton overhead crane ready for work to begin. It should perhaps be pointed out that the 4Cor Power car has only one powered bogies, that under the cab. The other end rests on a normal trailing bogie.

First is was necessary to disconnect some of the brake linkage from the brake cylinder under the centre of the coach, the motor leads and also to remove the keyway in the centre casting. The normal method of lifting is to slide bars between the coach body and the bogie and lift the body with the crane attached to the ends of the bars. However, Cor motor bogies are pretty big by modern standards and there was insufficient room to slide bars through. It was, therefore, necessary to place sleepers on the rails and, using a bottle jack resting on the sleepers, to jack up the body from under the headstock. Only a few inches of lift was needed but a great deal of sweat went into gaining this small amount of extra clearance.

Once there was enough room to slide the bars through, the lift could be started. With much creaking and groaning the cab end was lifted two to three feet (a very impressive sight) at which point the centre casting on the bottom of the coach was clear of the top of the bogie. The bogie was then hauled out as a trailer behind the Hastings Diesel Group’s DEMU and the body was lowered onto trestles.

We decided to tackle the underside of the body firSt I have to confess to feeling rather uneasy at first, going under a body merely propped up on trestles, but we all soon got used to this. The chassis of the coach body is constructed from “I” section RSJ girders with the wooden framework bolted on top. I expected to find that the floor was also of wood, but was surprised to see what looked like corrugated iron. The floor, like that of much more modern carriages consists of this corrugated steel with a composition material on top. Underneath all of this is a network of conduits for power and control cabling and air lines. The motor leads (a bit thicker than standard garden hose) connect into junction boxes on the coach centreline. The main electrical gear is situated nearer the centre of the coach and awaits our attention at a later date.

All equipment underneath appeared to be in excellent condition. The only real casualty was a pair of spark arrester plates placed, we believe, to protect conduits etc from sparks from the brake shoes. Probably the Cor originally had fibre brake blocks, but when cast iron ones replaced these—on motor bogies only—the sparks possibly became a problem and shields were required. The shields are only about 1mm thick and had rusted right through in some places. However, replacements were easily made by copying from the originals.

The centre casting on which the bogie pivots is a large, solid piece of steel fixed to the coach chassis, with a steel pin about the size of a rolling pin projecting vertically downwards. The pin fits into a recess on the top of the bogie, but it does not seem a great deal to hold a carriage in place! The work underneath the coach body consisted of cleaning, rust proofing and painting all the steelwork. The outer crust of dirt was first chipped away using hammers and rust was cleaned off with rotary wire brushes, using an extended head to get into awkward corners and in some places simply with hand held wire brushes and elbow grease. To my wife’s eyes the procedure seemed to be a matter of slowly transferring 60 years of dirt from the train onto me and then having it brought home to be washed off. After this process, the cleaned steel was coated in red lead which was followed with gloss black paint.

The work under the body was completed early in 1997 and it was then time to turn our attention to the bogie itself. Before much could be done inside, it would be necessary to lift the motors out (Figure 1 shows how the motors are mounted). I had often heard the term ‘axle hung, nose suspended’ and nodded wisely without really understanding what it meant. Now was my chance to find out.

The motors almost fill the space between the wheels. They rest on the axles in suspension bearings (see Figure 1) thus keeping the gear teeth on the axles (57 teeth) meshed with those on the motor shaft (the pinions, with 23 teeth). The remaining weight of the motor is taken at the nose end (see the shock mounts in Figure 1) where two large bolts for each motor locate it onto the bogie frame. Thick rubber bushes are interposed between the frame and the motor mountings to permit small movement and absorb shocks. The forces on these mountings may be either upwards or downwards, depending in which direction the motors are rotating.

To remove the motors, the suspension bearings must be dismantled. Each bearing is in two halves, each half having a gun metal liner with a white metal bearing surface overlaid on it and this forms the surface bearing against the axle. One half of the bearing is formed in the motor casing while the other half is bolted to it. The removable half must be separated from the motor case to release the motor from the axle. The light steel casing which covers the gears must also be removed, as also the tow bolts holding the motor at the nose end.

When lifting the motors, only the two lugs nearest the centre of the bogie are used. This allows the motor to tilt sufficiently to clear the frame, but lifting it vertically using all three lugs (again see Figure 1) would cause it to foul the frame. After removal, the two motors were rested on sleepers by the side of the bogie. Removal of the motors permitted access to the inside of the frame where serious cleaning, rust proofing and painting could now begin. Modern bogies tend to be of box section construction, but on the Cor the sides of the bogie are plates, similar to the frames of a steam locomotive and about 1"; thick.

Also contained inside the frame is the brake linkage—usually defined as rigging in the trade. Figure 2 shows, in simplified form, the action of the brakes. As the rod is pulled in the direction shown by the brake cylinder positioned further along the coach, the linkage holding the shoes goes out of square, into a roughly parallelogram form, and the wheels are squeezed in between, thus restricting their freedom to rotate. This linkage was also partly dismantled, i.e. the lower levers were removed, to allow the next stage of the overhaul to proceed. This was to lift the frame off the wheels completely. The axle boxes slide up and down in the bogie frame and after removal of the lower rods of the brake linkage, the bogie frame could be lifted off the wheels and axle boxes completely.

The bearings inside the axle boxes were another surprise to me, at any rate. The bearing journal only contacts the axle over a fairly small area at the top. See Figure 3 for a cross section of the bearing. Lubrication is achieved by a lambs wool pad sprung loaded against the underside of the axle, which soaks up oil from the reservoir formed by the lower section of the axle box.

Like the motor suspension bearings, the axle box bearings were all found to be in good order. The only items needing replacements were the oil seals on the inside of the boxes where the axles pass through was a piece of ½" plywood in a slot at the rear of the axle box. This had a hole of about 6½"; in diameter for the axle to pass through. Felt was wrapped around and tacked onto the plywood to form an oil‑tight wrap around the axle. (Felt was largely used for oil seals on shafts in automotive practice at that time.) The original seals were quite worn and the exact construction was not easy to follow, but with the help of advice from staff at various railway depots, we managed to fabricate suitable replacements. A rather surprising complication was that the diameter of the axle at each box was different with about 6mm (¼") difference between largest and smallest dimensions.

The next item of interest is the suspension. Figure 4 shows the primary suspension i.e. that which connects the axles boxes to the bogie frame. The weight of the bogie and one end of the carriage bears down onto the volute springs and therefore hangs on the equalising beam. The equalising beams are massive pieces of solid steel about nine inches to one foot high, around four inches thick and run the length of the bogie. Volute springs act exactly like the more familiar helical (coil) springs under compression, but their shape is flat, like the cross section of a clock spring.

If the wheels had independent suspension, any difference in rail height between the axles would put greater weight on the higher wheel. The advantage of the equalising beam is that where there is a difference in rail level across the bogie, the beam will tilt and apply some of the extra weight from the higher wheel to the lower wheel, thus tending to equalise weight distribution. Most modern bogies tend to use some form of equalising arrangement, the ‘Commonwealth Bogie’ being perhaps the best know example.

Returning to the axles boxes, when the bogie frame was lifted off it was apparent that there was a crack in the web connecting one of the axles boxes to the equalising beam. This had obviously happened before as was evident from repairs to the other similar parts. Fortunately, SLREL came to our rescue and welded the crack up in a similar fashion to the earlier repairs. From there it remained necessary only to clean, rustproof and paint the axles boxes ready for reassembly. While the axle boxes were off, the wheels were cleaned down and repainted. Being such a large area, the simplest way to do this was to use a compressed air driven needle gun. This made a good job of the wheels, but I had not realised that the compressed air expanding in the gun causes it to cool. Very soon a frost formed and my fingers ached! The trick is to wear thick gloves and to hold the gun further back.

With the wheels and the axle boxes now completed we could concentrate on the bogie frame. It can be seen from Figure 4 that all the weight hangs on the nuts at the lower end of the volute springs. Obviously theses nuts are very substantial 4½"; across the flats). It would have been desirable to undo these to remove the equalising beams, but after some heroic efforts only one of the nuts could be loosened, while the remaining three held faSt An attempt to make a special spanner came to nothing, so the beams had to remain in place. It was clear, however, that the springs were in good condition and it proved possible to clean, rustproof and paint behind the equalising beams quite satisfactory. Cleaning and repainting the remainder of the bogie frame was also completed at this stage.

The only item still requiring attention in the bogie was the bolster. Figure 5 shows the construction of the secondary suspension i.e. that between the coach body and the bogie frame. The bolster basically forms the top half of a spring sandwich. The lower tray hangs from the bogie frame by swing links. The coach body centre casting rests on top of the bolster. The springs in the middle of the sandwich are formed of transverse (fully elliptic) leaf springs which is an unusual feature. This type of bogie with equalising beams and transverse leaf springs is sometime know as an American pattern bogie. The bolster is free to swing from side to side to a degree, constrained by friction pads set inside the frame. As the train follows curves, the bolster will swing outwards. The swing links are not vertical, but at an angle as shown. This means that the side on the outside of a curve will rise while the opposite side will fall, thus causing the coach body to lean inwards around the curve. Who said tilting trains were new?

Figure 5 shows the bolster well below the top of the bogie frame. It has been shown this way merely to show the construction more simply, but in practice the top of the bolster is roughly flush with the top of the bogie frame. The bolster is prevented from being lifted out by two plates fitted on top of the bogie at either side. When the body is lifted off, the bolster springs‑up hard against the plates making it virtually impossible to unbolt these plates from the frame. It was necessary to lift the bogie back onto its wheels and lower the coach body onto the bolster in order to ease the pressure on the plates to enable them to be unbolted. The coach body was lifted off when this task had been completed.

It was possible now to lift the bolster straight out exposing the springs and the lower tray. The bolster and tray were cleaned and painted in the same manner as for the rest of the bogie. The leaf springs were found to be in good condition, but were not painted although red oxide had been applied at some earlier time. They were just coated in oil. Since the bogie was dismantled, it has been examined by staff from railway depots who have confirmed that it was all in good order. A number of other visitors to the depot also commented on the bogie’s good condition and, may I say, on the high standard of work being carried out on it.

Lastly, to the motors themselves. No attempt was made to dismantle these, but removal of the inspection plates to the commutators showed that both these and the brushes appeared to be like new. Perhaps the unit had been overhauled shortly before withdrawal or, maybe, the general standard is a tribute to its original builders. As an aside, the commutators are about 18"; in diameter and some 4"; in length (along the line of the axis). As far as I could see there are about 160 segments on the commutator. The motors were then cleaned externally with rotary wire brushes, an awkward job because of the fins on the surface which are there to assist cooling. Red lead and engine lacquer (to withstand high temperatures) were used to complete the job.

Eventually, after almost a year of work, the time came for reassembly. First the top section of the bolster; this simply slots onto ridges on the top of the leaf springs. However, when the weight of the bolster was removed, the springs sagged outwards as a result of the weight of the equalising beams resting on the outside, so when the bolster was lowered back it was not in alignment with the ridges. To bring the mating parts into alignment it was necessary to lift the outer edges of the springs with the crane until the bolster dragged into position. (Further study of Figures 4 and 5 may assist in understanding this point.)

With the axle boxes lifted back onto the axles, the complete bogie frame was lifted back on top and the motors lowered into place. As the motors were lowered it was necessary to hold the top half of the suspension bearing shells in place—located on top of the axle. This was achieved by two people standing underneath and holding them in place with pieces of wood—one each side of the axles—a little unnerving with four tons of motor dangling overhead! Once the motors were in position, the remaining half of the suspension bearings could be reattached. It was interesting to note that there are no keyways or dowels on the bearing housings to locate them precisely and it was necessary to rock the motor from side to side (using the crane of course), until the two halves of the bearing lined up correctly.

The gear cases were then fitted over the gears. The cases are constructed in two halves with grooves around the cut away sections which the axle and motor shafts pass through. The grooves have felt fitted into them, held in place by rivets. Felt seemed to be the universal oil and grease medium on the bogie and needless to say the felt had to be replaced. The gears are lubricated by grease. As an aside the grease (Crate Grease) used to lubricate the gears is extremely thick and has to be warmed before it can be poured into the case. Its effectiveness is legendary and a story goes that someone once decided to put it into the axle of his car. Once the grease cooled the axle set completely solid!

A final job was to clean out the well on top of the bolster in which the coach body’s centre casting sites. This is basically an oil bath with a friction plate similar to the clutch plate on a car, located between the coach and bolster. The coach body was raised and then lowered back onto the bogie once the latter had been levered by hand back into the correct position. Again the body had to be lowered in stages, using a jack for the final stage, because of the problem of insufficient clearance between bogie and coach body, as defined when detailing the manner of lifting the body off the bogies to start the overhaul.

The whole reassembly was very much quicker in fact than the dismantling, with almost all of it completed in one day. This was largely because a lot of help was provided by SLREL staff and Hastings Diesel Group volunteers. Once reassembled it was possible to haul the motor coach from under the crane and shunt it onto one of the other roads in the depot. Adjacent, in fact, to the other four Cor vehicles and the 2Bil.

The bogies has required a great deal of hard work and, like all such jobs, has taken much longer than originally envisaged. It does, however, represent a major step forward in the preservation of the unit. We know the bogie is in good condition as well as rust proofed and painted and it is an achievement of which we are all justly proud.