Overhauling a Steam Tractor.
Page 15
Page 16
If you've noticed an error in this article please click here to report it so we can fix it.
By an Engineer-in-Charge.
Before commencing the overhauling of a steam tractor, an examination should be made of all the parts, and those details which require attention should be carefully noted. If this operation is carried out in an intelligent manner, unnecessary work will be avoided. There is no useful purpose served by indiscriminately taking apart every detail of the tractor simply to put them together again, and I would like to advise drivers and mechanics not to scamp anything when doing an annual overhaul, as, if the tractor is then kept in the shops a day or two longer, for the purpose of completing the necessary repairs and adjustments, it is more than probable that the owner of the machine will be saved subsequent annoyance through failure of any particular detail.
Cylinders and Pistons.
The first parts which should claim attention are the cylinders (I will assume that the tractor under discussion is one of the compound type), and if, on examination, they are found to be cut and scored, or worn more than one-sixteenth inch, it will be necesiary to have them rebored and new pistons fitted. If, however, they are not worn very much, but have a hard, glossy surface, a new set of piston rings, if carefully fitted, may be all that is necessary. When re-boring a cylinder, the boring bar should be set dead true with the bore, and, with a roughing tool, a cut should be taken without stopping until the tool has passed right through the cylinder. With a fiat tool that has been carefully honed, a finishing cut should then be taken in order to scrape out the marks left by the roughing tool, and so leave the bore clean and smooth. A rough casting of a new piston should now be obtained from the makers, and this should be turned to fit inside the cylinders, and, unless the piston rod can be skimmed in the lathe, the hole in the piston will have to be reamered to suit the piston rod.
Slide Valves and Starting Valves.
The slide valves will next require attention, and if these are badly scored it will be necessary to re-plane and surface them again with the scraper. In cases where a lot of metal has to be taken off, it may be necessary to pin on to the valve a false face, and this should be planed up on bnth sides and securely pinned to the valve, the adjacent faces having previously been smeared with a thin paste of red lead. The false face should be secured to the casting by means of countersunk screws recessed abont one-sixteenth inch below the level of the face. Each slide valve should then be planed and surfaced. The required thickness of the false face may be ascertained after placing the slide valve on the rod, keeping it as far away as possible from the face of the ports; the thickness to which the false face must be planed is obtained by measuring the distance from the face of the slide valve to the surface on which it slides. After being fitted with a false face, the valves should be tried by hand before being coupled up with the steam-chest cover in position; this in order to make sure that it is not too far out and likely to seize when the cover is bolted on. The glands of the neck bushes will have to be rebored and bushed with gunmetal, leaving on the end of the bushing a shoulder about I in. wide, whilst the diameter of the shoulder should be the same as the outside of the glands; when the gland is screwed up, the packing will then keep the bush in place. The neck bushes should be new ones, and these can be turned and bored out of a piece of solid material. The faces of the starting valve, if not already steam-tight, should be carefully surfaced.
Cross-heads and Guide Bars.
The cross-heads will certainly require adjustment, and, if no provision for adjustment has been made by the maker, the bars, if of the parallel type, will have to be moved closer together. As most of the wear takes place on the bottom bars, and is greatest at about the centre of their length, they should be tried with a straight edge, and, if worn to such an extent as to require it, they should be replaned, but in doing this a witness" should be left along the centre of the valve. By that I mean for a width of about one-sixteenth inch the metal along the centre should not be cut away, but should be left standing proud of the planed. surface. The bars should then be replaced on the engine, with the crossheads in position, in order to ascertain ha v much metal must be taken off them in order to allow of their coming together, so that the cross-heads may be a free sliding fit for the whole length of their strokes. The amount which will have to be taken off the bottom bars may be found by the insertion, under the bottom of each crosshead, of pieces of tin, or thin sheet iron, just thick enough to bring the cross-heads up to the top bars; the piston-rods and glands should be in position while these dimensions are being taken, so that the glands may be tried with the pistons at both ends of their strokes, in order to make sure that the rods are quite free. Great care should be exercised in the filing and planing of the bars, as it is quite an easy matter to get the faces canting in relation to each other when tried with the straight edge across the bar. They should also be most carefully bedded down on to the brackets before the bolts are tightened, or it is probable that the bars will be twisted out of shape. If too much scraping and planing has been done, and the bars are, in consequence, rather too close together, they may be separated by the insertion of brown paper or tin lining. The crosshead pins and brasses in course of time wear oval, and the pins may have to be renewed; the brasses, however, may be used again if they are not very badly worn, by cutting them back a little and re-scraping them to fit the pin. The oil grooves should, of course, be cut a little deeper.
Big-end and Main-bearing Brasses.
The big-end brasses will be found to have worn considerably more than those of the small ends, and new ones will most probably be required. This is far preferable to lining the old brasses with white metal, as is sometimes done, in order to save a little expense; white metal is very satisfactory in cases where neither dust nor grit are likely to find their way into the bearings, but, in this class of engine, the grit from the road and the small ashes from the funnel are liable to score them very badly. Before taking the measurements for the thickness of the big-end brasses, the following conditions should be produced :—the connecting rods should be coupled up at both ends; the piston rods must be keyed to the crossheads; if necessary, liners must be inserted in the crossheads to bring the cotters up until they project just far enough through the straps to enable split pins to be inserted in the first holes; and, the clearance between the pistons and the cylinder covers at both ends of the strokes should be found. The old brasses can then be put back and coupled up with suitable liners to bring the pistons back to their original relation with the cylinder covers, and the thicknesses of the new brasses may then be obtained by adding to that of the old brasses the combined thickness of the liners. If there are no "stroke marks " on the guide bars, when ascertaining the clearances due allowance must be made for the expansion of the boiler, as, when under steam, the cylinder is carried further away from the crankshaft.
In the ease of the crankshaft bearings, if it is necessary to renew these, the crankshaft webs should be tried to make sure that they are parallel with the face of the guide bars. This may be done by laying one straight edge across the webs of the crank, and another across the bottom bars, and, by carefully sighting along the edges, note if there is any lack of accuracy ; if one side shows " low," a liner must be placed under the hearing at that side, to bring it up until both the straight edges are parallel. The thickness of the liners must be allowed for on the new brasses. The journals, as well as the crank pins, if scored, may be trimmed up smooth in the lathe, but in most cases a good polishing with emery cloth and oil will be sufficient.
Link Motion.
The link motion should be examined, and the die block, and any slack pins should, if necessary, be renewed. All the hardened parts should first be softened and the holes reamered, and new pins mu then be fitted, after which all the parts should be re-hardened and the pins ground into their ruse,..setive holes with flour emery and oil until they are a lice working fit. The guides for the slide-valve rod, if necessary, should be provided with gun-metal sleeves, and these must be bored to suit the slide-valve rods. The eccentric straps should be let together, and, if necessary, eased off at the top and bottom ; if it is found that the " go-ahead " strap is worn badly, it may possibly be changed over with the " go-astern" strap.
Transmission Gearing.
The engine should now be jacked up, and stout wooden blocks placed under the firebox so that the wheels may be removed and the second motion shaft withdrawn and carefully cleaned and examined for any defects. The gearwheels also should be cleaned and scrutinized, and the keys tried to make sure that they are not slack. If any of the keys are found to be loose, and it is impossible to drive them home any further, they should be removed and new keys carefully fitted. After they have been fitted so that they show a good bearing all over, and will just tap in to within about one inch of the gib or end, the wheel may then be made hot, in order slightly • to expand the wheel boss, and the key driven in with a key set and a heavy hammer_ The feathers in the crankshaft should also be examined, and these should be a good fit sideways, and should also be tight in the crankshaft ; if these conditions do not prevail, new ones will have to he fitted. It may he necessary to fit a new high-speed wheel and a corresponding high-speed pinion on the crankshaft, as these wheels are found to wear faster -than those of the low speed. The teeth of the new wheels should be carefully examined to see that they do not " bottom," as the wheels are rotated. The small pinions of the differential gear must be examined, and, if found at all slack, must be bored and bushed, and probably new steel pins will be needed. At the same time, while examining these wheels, as in fact 11 other parts of the tractor, ,every bolt and nut shou be carefully examined, and, where necessary, tighten up hard. The bushes in the second motion shaft as rule do not wear very much, but they should be trier to a .certain if they are tight in the brackets; if slack, they should be secured by the insertion of a set pin.
Axles, Brakes, and Steering Gear.
The axle-box brasses should also be examined and renewed if necessary, and the axle itself closely scrutinized for flaws or cracks. The front wheels may now be taken off and an examination made of the axle and springs, and if there is excessive end play an the wheels or spring pins, suitable washers should be inserted. The brakes should next receive attention, and should any doubt exist as to whether any particular part requires to he renewed. the engine should be given the benefit of the doubt, and the parts should he scrapped and replaced by new ones. The operating screw and nut may need to be replaced by new ones, and, in all probability, new wooden brake blocks will be required. If a flywheel brake is fitted, these blocks should also be examined and renewed if necessary. The steering gear should be overhauled and any end play between the worm shaft and the bracket should be taken up by the insertion of a washer. The chains ought to be taken off the drum and passed through the fire, and, while each link is at a dull red heat, it should be examined for cracks. The chains should then be allowed to cool slowly. The eye bolts must be taken out of the chain roller, and these should be examined, as also should the adjusting screws ; if the latter have been screwed home and are incapable of further adjustment, a link should be cut out of the chain. When the steering gear is put back in place, and the chains coupled up, a quarter of a turn of the steering wheel in either direction should tighten one or other of the chains.
Boiler and Steam Fittings.
The boiler should now be stripped of its lagging; tube plates and tubes should be cleaned, fire bars taken out, and all dust removed from both inside and outside of the boiler. Thus stripped, the boiler is in a favourable condition for examination by the boiler-insurance inspector, who will advise what repairs are needed. All cocks on the boiler should he taken cs.t and ground in with a little flour emery and oil, and finally greased with Russian tallow before being replaced. The gauge glass should be taken out, the cocks ground in and repacked, if of the packed type; a piece of stiff wire should be passed through these fittings to make sure that the passages are quite clear. The safety valve may now be disconnected and cleaned ready for the boiler inspector's examination, and the pressure gauge should be removed, so that he may compare it with his standard instrument. All pipes should be disconnected and carefully examined for splits or cracks, and cleared of dust and foreign matter which may have lodged in them. Especially does this apply to the suction pipes for the pump or injector. The strainers also should be examined, and the tanks cleaned out. In most cases it is advisable to send the injector to its makers for adjustment or repairs.
Reassembling the Tractor.
The tractor should now be reassembled, and great care should be taken, when screwing up the bearings, to ensure their being quite free, and with a little end play. As the parts aro assembled, they should be wiped free from all grit and smeared with cylinder oil. The flywheel should be pulled round frequently by hand to make sure that each part as fitted is quite free, and all oil holes and grooves should be carefully cleaned, and new worsteds fitted in the oil cups. All joints, with the exception of that of the steam-chest cover, may now be remade: the steam chests should be left until the last, so that the valves can finally he " set " when the engine is under steam. When the assembling of the tractor is complete, the engine can be taken off its packing, the fire bars and ashpan replaced, and the fire kindled. As the steam pressure rises, and while the lagging is still off the shell, the boiler may be examined for any leaky seams or rivets, and if there are any signs of weeping,, the faulty joints should be caulked up. When steam is up, all the joints and glands should be examined and locked hard up. The engine should now be allowed to run slowly for some time, during which time careful observation should be made of all the bearings, and plenty of oil should be supplied to the working faces, especially in the cylinder. After running slowly for a little time, a wooden lever may be placed under the flywheel, so as to have a braking effect, and steam may then be turned full on in order to test the engine, and so show up, by the application of full steam pressure. any joints that are not quite tight. After surplus oil has been removed, the lagging may be replaced on the boiler and the cylinders, and whatever painting or varnishing is required may then be undertaken. After such an overhaul, it is best not fully to load the trailer for the first journey. A light load will give the engine a chance to bed itself down, whereas, after an engine has been overhauled, a heavy load might result in more wear in five minutes than in a year's ordinary work.