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OVERHAULING AN UNDERTYPE STEAM WAGON.

9th August 1921, Page 22
9th August 1921
Page 22
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Page 22, 9th August 1921 — OVERHAULING AN UNDERTYPE STEAM WAGON.
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No. 18.—The Sentinel Four and Six Ton Wagons.—Useful "Wrinkles." from the Makers Own Repair Shop—Special Tools for Certain jobs—How to Set the Engine Valves, and Other Hints.

IT IS probable that more information has been disseminated in regard to the maintenance and repair of petrol vehicles than has been the case .with the steamJ-driven variety, 4/et, as the repair shop man-must needs, at ernes, act in the capacity of general practitioner, it is as well that he should he as familiar with the one type of machine as with the other, even though the petrol-driven variety predominates on the road.

Workshop Facilities for .Steam.

In this article, therefore, bearing in mind the fact that, in recent times, there has been a considerable increase in the number of steam vehicles in use— particularly of the make with which we are now dealing—we shall address ourselves, perhaps, more to the man whose previous experience has mainly been .amongst petrol vehicles and who finds himself faced with the necessity of tackling a steam wagon overhaul, than to his more experienced brother to whom the steamer may be an " open book."

The main point for a man, with no previous experience of steam, to bear an mind is that while. the steamer is generally a more robust and, perhaps, less complex vehicle than the petrol wagon, it is heavier in its main details—partly on account of the greater tonnage it is designed to carry. It is as vell, therefore, before starting on an overhaul, to ensure that substantial lifting tackle is available, and that workshop facilities are adequate for the various operations that may have to be carried out. A steam wagon crankshaft., for instanee, is a very different affair from that, of a petrol engine, and its connecting rods —though fewer in number—are much more massive than the corresponding petrol engine details. Bed-' ding in big-end brasses is, therefore, a heavier operation and must be tackled accordingly. For thia, reason, also, it is, perhaps, desirable not to disassemble the chassis more than is essential for the execution of such repairs as are diagnosed from syrup.toms to be necessary.

Features of Sentinel Construction.

While, on an" overtype " wagon, the engine, as a unit, is obviously accessible, on an undertype wagon, such as the Sentinel, with the body of the wagon "in situ," the reverse appears to be the case. It. will he found, however, that the engine, can quickly be dropped from the chassis, and, tackled as a separate unit, on suitable trestles, and that, with the wagon body taken off, a fairly complete examination can even be made of it without removal. The almost

ideal simplicity of the undertype transmission gear has attendant advantages, from the repair shop viewpoint, as well as presenting a neat appearance. The vertical boiler is conveniently designed to allow of a maximum of accessibility with as little disturbance as possible. It is convenient, for instance, to drop the firebox and gain access to all important parts for cleaning and examination purposes, without removing the driver's canopy. This method we shall describe.

So far as the engine is concerned, valve setting, that operation winch tradition, in steam practice, has shrouded in a kind of mystery, presents little difficulty. The valves are of the poppet type, cam-actuated, and, in consequence, even the man with no previous experience of steam, can approach the matter of their adjustment without misgiving. Detailed instructions as to valve setting will be given later.

For the rest, it :should be noted that the makers have had the foresight to produce a very complete set of valve facing cutters, reamers and gas taps, suitable for dealing with every valve seat and guide which may need attention. 'The literature, also, which Ole.37 issue for the use of their wagon owners will be found most useful, and we must acknowledge our indebtedness to much of it, in the preparation. .of 'this article.

Dismantling for Inspection.

For the examination of the boiler, inspection of the firebox and tubes, and for cleaning purposes, the firebox must be dropped. To do this the canopy. need not be taken off, but the funnel and the circular boiler stud cover must be removed from the boiler top and the steam super heater coil lifted out, after uncoupling the two flanges which hold it on either side. The ashpan having been dropped, a chain sling can now be passed through the hole in the canopy, down through the centre of the firebox, to enable a stout bar (as shown in an illustration) to be passed through it and thus enable the weight of the box to be taken. The removal of the ring of nuts which hold it in position above and below, will now permit the firebox to be lowered bodily from the boiler shell. Cleaning and scaling is now possible, and any tubes which may require such attention can be tackled with a tube expander. The

Turning cam quadrant to move camshaft thoroughly cleaned out. The blast to required position. nozzle should also be examined, as it may become choked, due to the carbonization of oil. The stoking shoot should alio receive attention, and, if the bottom half is found to be badly burned. by the fire, its renewal is desir

able.

With the body platform removed, the engine drops from the chassis, after.uncoupling all pipes and connections and removing the bolts which hold the suspension side plates to the frame members. This unit is fairly heavy, and due allowance should be made for this in slinging. A note may here be added as to the necessity for thoroughly cleaning the engine before opening it up. Owing to its position, it is liable to accumulate a lot of dirt. The removal of the axles calls for no special 'comment and, unless the water tank_is leaking and in need of special attention,. it. will probably be convenient to leave it in position. When the units have been removed, the chassis should be well cleaned and thoroughly examined all over for pos. &Bole flaws, and for rivet looseness. ,A loose ri-vet should be replaced by a, well-fitted bolt.

Some Minor Points.

Valves, cocks, and all boiler fittings should be put in good order, if any of e27. them have shown a tendency to leakage. The cutters supplied by the company enable the safety valve, feed check valve, and auxiliary valve seats, amongst others, to be trued up. Leaking cocks can be put right by smearing the plugs with very fine emery and oil and regrinding them in their barrels. If aplug of.this.kind is found to be really badly scored, it may he necessary to true it up first in a.lathe, in which case the shoulder may have to be filed to allow the washer to seat against the barrel, as otherwise it may he impossible to tighten it, and, it may be necessary, sometimes, to open out the hole a little to enable it. to register properly and, so, to avoid constriction.

The foot release valve should be given especially careful attention, as aleak here may be the Cause of a considerable loss of steam, which goes direct to the funnel each time the stop valve, is opened. Also an important valve, the condition of which is frequently neglected, is the pump by-pass valve. It should be remembered that, in the Sentinel design, the )3unip is continually working, so the importance of the by-pass valve condition will be appreciated.

The packing on all valve stems should be inspected and renewed if necessary. Piston rod packing especially should be examined. A large amount of steam may be wasted if the packing has perished, and water thereby accumulates in the Crankcase.

Great care should, however, be taken not to tighten up this packing unduly, especially immediately after it has been renewed, This is a common fal:lt, and it is really only necessary to tighten up the nuts on the gland studs lightly with a spanner, or even with the finger and thumb.

. The Engine Unit.

• The main crankshaft bearings are not split, and push over the ends of the shaft. When refitting these, it is advisable to test the fit of the shaft by taking the weight in the manner shown in the photograph we reproduce, and slowly turning it. When fitting the left main bearing, the housing of which carries the camshaft driving shaft, the meshing of the bevel pinion with the corresponding wheel on the crankshaft should be verified. Care should be taken when coupling up the two halves of the camshaft driving shaft to pull them towards each other, and then slack back about 1-64th in., in order to ensure that the gears at each end do not engage too deeply.

As regards the valve Operating arrangements, the following is the correct procedure to follow :—To inspect the camshaft, first -disconnect the reversing gear near the cambox, remove the end door from the latter, then take out the eight valves and their springs and covers. In

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replacing these, it is important to put each back in the place from which it came. Then push the short control lever on the eambox as far as it will go towards the crankcase, and pull the camshaft right out. If the small, or ".fast,' steam cams are much worn, the shaft should be renewed. Before replacing the shaft, the push rods should be withdrawn and examined. This can be done without disturbing the cainbox, by using a special tool supplied by the makers, which enables the rods to be withdrawn through the bore of the canabox. Worn rods should be replaced and, if necessary, the guide holes can be opened out to flin. diameter and rebushed with special bushes.

In replacing the camshaft, ease the push rods out of the way of the shaft and, in entering the latter, make sure that the finger on the inner end of thecontrol shaft engages with the wide •groove in the camshaft.

Thea'couple,up the reversing gear, with the lever in the " forward" starting notch, and measure the distance from the end of the camshaft to the face of the bevel wheel. On all wagons up to and including No. 232, the end of the shaft should project Ain. beyond the fate of the bevel wheel. On later wagons it should be -13ain. inside the face, unless there is another dimension, stampedon the shaft end. In such a case work to that figure.

If the setting does not suit the-reversing link, as adjusted, lengthen or shorten the latter.

The valve seats can now be reground if necessary and the valve stems tried for clearance. There should be a bare 1-64th clearance between the valve stem and push rod ends, with the valve hard on its seat. Valve springs may weaken in time and should be tested. A new steam valve spring is 2g ins, long when free, and a load of

9 lb, compresses ii in. A new exhaust valve poring is 21 in. when free.. and compresses the saim amount with a 12 lb. load. A spring can safely be used until weakened by 25 per cent., that is to say until the loads given compress each spring

After that point replacement is desirable.

How to Set the Camshaft.

K e•ep the reversing lever in forward start notch. Then remove chain and get your assistant to turn the engine with a spanner or -chain pinion nut in the direction tending to screw nut on, as shown diagrammatically. Remove the trunk door on left-hand side (or pump side) of engine and let your assistant turn the engine until the piston on that side of the wagon is exactly at the end of its stroke (nearest boiler). With a knife or scriber scratch a line on the piston rod flush with the packing gland (illustrated). Be careful that the gland is not

loose and floating about with the rod. Then, for the time being, do not move the engine. Now put the valve stem and guide in plaee, i.e., the second valve from the left-hand side of the front end, and bring your assistant round to the left side of wagon. He will then be able. to rotate the camshaft by turning the cam quadrant, as shown. With your one hand hold steam valve cover in position and with the other press the valve on its seat. Now get your assistant to turn the amshaft two or three times, until you know exactly where you are ; then stop him just at the point *here the valve is commencing t) lift, and -couple the cam quadrant ; one bolt will be sufficient to hold this for the time being. Your assistant should now turn the engine back slightly with the spanner on the chain pinion nut, while you hold the same valve as before on its seat, and watch the line you made on the piston rod. When this has travelled about in. or so from the packing gland tell your assistant to turn the engine in the forward direction very slowly. Watch the line on the piston rod carefully, keeping the valve on its seat, and just as the line reaches the packing gland (or the • piston arrives at the end of its stroke) the steam

• valve should commence to lift. If you are not quite certain of this, tell your assistant to -turn the engine a little way backwards again, and repeat as above. If, while holding the valve on its seat, you) at the same time, try to rotate it with your fingets, you will know exactly when it starts to lift, as it is difficult to rotate while on its seat, but quite easy as soon as it lifts. When one valve is correct the others will be properly timed.

It should be noted that all steam valves should start to open with the piston exactly at the end of its stroke, with the reversing lever in forward start position.

Random Repair Shop Wrinkles.

In the . space at our disposal, it is impossible to cover every feature which may need. attention at the repairer's hands, so we will conclude with a few

haphazard hints. . . .. Firstly, as to driving chains. It should be noted that the makerscan supply special chain cleaning and lubricating pans for the proper treatment of these important parts, according to instructions which they also supply. Proper treatment will double the life of a chain. Chain pinions can be removed easily with a special draw-off gear made by the makers. Driving chains are easily put on or taken off by pulling the ends together with a piece of rope, as shown in the sketch.

In fitting rear axle bushes, it should be noted that, while they should bear along the whole length of the crown, they should only touch about 4 ins. circumferentially.

The brake radius rods should always be adjusted to correspond with the main radius rods, in. order to keep the axle box in a vertical position. Piston clearance should always be checked after the crank pin bushes have been adjusted.

When fitting new brake linings care should be taken to ensure that the holes are made a geod fit for the fixing screws. After replacing front or rear road wheels, screw up all nuts as tight as possible. This injunction applies to nuts all over the vehicle, with the exception of stuffing box gland nuts. The• check valves should have about •AT in. lift.

End play in wheels is taken up by fitting specially thick thrust washers. Oversize cross-heads can obtained if necessary to compensate for wear. When lining up front wheels, set them slightly " narrower " in front. If axle box bushes wear badly on the flanges, replace by special bushes, or, in emergency, rivet a semi-circular piece on the worn surface. See that there is not too much play between the stop valve and its spindle. Finally, we must express our thanks to Mr. George Woadvine, of the Sentinel Waggon Works, and to his assistant, Mr. Philp, for the facilities extended and valuable assistance given us in the compilation of these notes.

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