WINTER WORK IN THE GARAGE
Now is the time to carry out an overhaul of your car, and in the following article will be found some useful information as to the best means of setting about the work. THE philosophers who write in the daily newspapers at this time of year are constantly telling us of the advantages of winter, as being a time to improve our minds while yet keeping our bodies in good condition. Not many of these gentlemen, one would fancy, are
the owners of sports cars, but the same reasoning applies. Instead of facing the icy or watery blasts which are reputed, not without reason, to make ” Grey Englishmen,” two or three week-ends spent in getting to know the inside of the motor-car will be repaid by added enjoyment later on.
Tools and Tackle. The examination of engine and chassis
is not a difficult matter, and can be carried out with simple tools and tackle. For the first, a set of fixed-jaw spanners of good quality, such as the B.S.A. series, will be required, and there ought to be a complete set provided with the car, which can be used for dealing with the other end of stiff bolts. Substantial box spanners are also worth having, and the thin fixed spanners made by Terry’s are often useful for reaching inaccessible nuts. Pliers, adjustable spanners and a hammer form part of every tool kit, but two or three screwdrivers with blades of different lengths and widths are worth having. Some bastard-cut and smooth files, and a supply of grinding powder, jointing compound and emery cloth complete the list.
A work-bench can be constructed on a framing of 4 by 4 inch timbers, with a top of one inch boarding, a convenient height being about 36 inches. A vice with a jaw-opening of six or more inches will be needed, and this should be fitted over the right-hand leg of the bench, so as to transmit any strains put on to it direct to the floor. Several wooden boxes for holding large engine parts and some tins for the smaller items will be required, and it is wise to have at hand an assortment of Whitworth
and B.S.F. nuts and bolts, with suitable spring and plain washers, also split pins, in ease any of these items are damaged *when taking .down the car. A .spare cylinder-head gasket and also a couple of valves and saute valve-springs should be obtained before operations begin.
The Garage. In order to work comfortably in a
In to a garage, some form of heating is almost essential, and. the tall paraffin stoves, or of course an electric fire if there is a power-plug available, are very handy. On a concrete floor it is wise to stand on the lid of an old packing case, or even to construct a ” duck-board ” to go in front of the bench.
The first component to be dealt with in an overhaul is the engine. If the cylinder block has been removed within, say, the last 5,000 miles, it should not be necessary to do more than remove the head and decarbonise it, but if the car has undergone a season’s work with nothing more than “top overhauls,” and in any case if the car can be spared for a sufficient time, an examination of the pistons and big-ends should be made.
Whichever course is decided upon, the first step is to drain the radiator. The carburetters will usually be left in place, but all controls and petrol pipes have to be detached, and also exhaust pipes, plug leads and the top radiator connection. In the case of overhead-camshaft units the maker’s instruction book should be consulted to find out whether there is any method of ensuring that the timing shall not slip when the drive is detached.
Dismantling the Engine.
Most modern engines have a sprocket which can only be secured to the camshaft in one position and which is held in contact with the timing chain by a stirrup, but otherwise it will be necessary to mark sprocket and chain links with white paint, and to lint a length of wire
through the chain before detaching it, to prevent it falling into the depths of the crankcase. Marking will also be necessary with shaft-driven camshafts if the driving gears have to be unmeshed.
Th instruction book is or should be useful to find out which are the nuts of the cylinder holding-down bolts, for on an O.H.V. engine some of these appear to be used simply for securing the rockerstandards, and their real use not suspected until efforts to lift the head have failed. On Alvis and Meadow engines the water is led from the cylinder block to the head by aluminium ducts at each end, and these also must be taken off.
The Head and Valve gear.
The head can be raised from the cylinder-block by inserting screwdriver’s on both sides and levering up evenly, but they should . not be forced in too far, otherwise the gasket may be damaged. On many engines lugs are left on the castings, and are bevelled to make it easy to insert the wedges. A head which is difficult to move may often be shifted by turning the engine round slowly with the starting handle. The head should then be lifted off its studs and placed on the bench. The cylinder bores sh mild be blocked with pieces of soft rag to prevent dirt getting down, and a sheet of brown paper pressed down over the studs will complete the protection. The first step in dealing with the cylinder-head is to remove the sparking plugs and the valves. Some makers supply a valve extractor in which one arm passes through the plug hole and bears on the bottom of the valve, while the other arm is hinged to it and has a forked end which depresses the valve spring cap, and allows the valve cotters or collets to be taken out. If a valve extractor is not used, one has to put on the bench a cotton reel, a nut or any other small object of the correct size to support the valve-head, and to depress the with an
the spring cap with an openjawed spanner, and at the same time fish with a piece of wire to remove the cotters. If the spanner slips, as it probably will do, the cotters will be shot across the garage and will take some time to find, so the extractor is to be recommended if one is at all short-tempered. The inlet valves should be a good. fit in their guides, otherwise air-leaks will occur, weakening the mixture and making starting difficult. If the valves are difficult to remove, in the case of the inlets, this may be due to using low-grade fuel, which will leave a gummy deposit, or from burring-over of the cotter holes used for the square type of cotter, in which • case the stem will need to be filed. Alternately the valve may be bent, either through hitting the piston through over:revving, or by being distorted
by heat in the case of the exhaust valve. In any case, bent valves should be replaced.
Valve heads are usually stamped with numbers indicating their position in the engine, but if this is not so the valves should be arranged in a drilled and numbered block of wood.
The tension of the springs which have been removed should be compared with a set that have not been used, and weak ones replaced.
Decarbonising the cylinderhead presents no difficulty, though everyone as their own idea as to the best tool to use. An old knife or a blunt screwdriver serves very well, and scrapers specially made for the purpose can also be bought. Care must be taken to clean thoroughly the surface against which the gasket beds, again with a blunt instrument so as not to scratch the smooth face of the metal. If the valve face and its seating in the cylinder-head are badly pitted, they should be re-faced, an operation which is best carried out by a garage, as it will not pay the private owner to acquire the special cutting tools only to use them once. The valve and its seating must be smeared with one of the valve-grinding compounds sold for the purpose, and rotated backwards and forwards over a small arc a few times, and turned to a new position. If no special tool is provided in the tool-kit, a hand-vice is useful for gripping the stem. On wiping off the compound, a polished ring, which is the sign of a good seal, will appear, and the final touches may
abrasize must be carefully removed from valve and seating with a petrol-soaked rag. After the grinding-in operation has been completed, the valves and. their springs may be replaced in the head. Stiff springs may be compressed in the
it can be cut with a knife blade, and if a piece gets left inside the spring, it can do no harm. The sparking plugs should now be taken to pieces and cleaned. Soaking in petrol, or, in the case of engines in which caster
vice, after first threading through them three pieces of strong string. These are tied tightly and the springs, caps and base oil is used, benzol or alcohol will loosen the carbon and a scratch-brush or emery paper will clean up a porcelain
be given with a fine paste if two varieties are included in the tin. All traces of the cotters can be replaced in comfort. is better than wire in this connection,
insulator like new. A cloth is better on mica insulators. Re-assemble the plugs and set gaps to 15-18 thousandths for magneto and 28 for coil ignition.
This completes the attention to the cylinder-head, which may be laid aside until the next operation is carried out, or replaced if it is decided not to further with the engine overhaul.
The next move varies according to the type of engine. the cylinder block and crankcase are cast in one unit, the sump will have to be dropped and the bottom half of the bigends removed before the see the light of day. With a detachable cylinder block, matters are much simpler. If the valves are push-rod operated, the rods should be removed and stored in the order in which they were fitted in the engine, as their lengths may vary slightly. The cups should be examined to see if there is any sign of flaw in the casehardening. The lower connections from the have to be taken off, and
removing the nuts of the crank case studs the block should come away easily.
Assistance at this point is almost essential, and an overhead tackle, particularly the chain-type which does not rim back when the down-haul is released, is a great help with a heavy engine. One member of the crew then lifts the block as steadily as possible while his partner steadies the pistons and prevents them striking the side of the crank-case when they emerge from their bores.
Pistons and Bearings. Gudgeon pins may be secured in a
pins may be in a variety of ways, usually by spring rings which prevent them moving sideways in the piston webs. Quite often they float both in the small end and in the piston, and are prevented from wearing the cylinder bores by a pad of aluminium at each end. If there is any Sign of scoring on the cylinder-wall it means that the pads are not working properly and must be changed.
The pistons should be removed from the connecting rods after marking them to show which cylinder they belong to. and which way round they were fitted. The carbon inside the crown should be scraped out and the top will naturally also be cleaned, taking care not to scratch the soft alloy.
The piston-rings should be free in their grooves, without any up-and-down movement. The rings should be removed by sliding them over three strips of tin equally spaced round the piston, and the grooves freed of carbon. If there are brown stains on the piston, it shows that compression has been escaping, and if new rings do not effect a cure, for maximum efficiency the engine should be re-bored. It is important when fitting new rings to see that there us a clearance between the ends, which should be about 10/1000 inch on a 3-inch piston, otherwise they will touch when the engine gets hot, and seizure will occur.
The condition of the bigends can be determined by taking hold of the connecting-rods. A little side-play is permissible, but there should be no up and down movement. If there is, the big-ends require attention before complete failure takes place. The cylinder-bores should now be examined. They should have a high polish, though floating gudgeon pins often mark them slightly without any loss of efficiency. Severe gudgeon-pin scoring should be built up by one of the welding firms who spedalise in this repair, while deep cuts may necessitate re-boring. Sometimes one finds traces of aluminium, the result of a temporary seizure, and the corresponding high-spots on the piston
should be taken down with a smooth file.
If it is necessary to take out the engine to attend to the big-ends or main bearings, this should be done while the head and block are not in place, since without their weight it is much easier to handle. On a few engines it is even difficult to remove the sump easily unless the bolts of the engine bearers are slacked off and the crank-case slightly raised, so the same thing applies.
The sump is usually secured on a number of studs, and a few shrewd blows with the shaft of a hammer may be needed to shift it. Care should be taken to avoid damaging the gasket, if one is fitted, though a replacement can be made from strong brown paper. The oil of course should be drained out before dropping the sump.
Care should be taken when dismantling an engine lest the valve timing be disturbed. In this M.G. Midget engine the camshaft bevel is marked, and the position of the bolt on the vertical drive coupling should be noted.
Cleaning the Sump. Before cleaning and washing out the
base-chamber, the contents should be examined for water, which points to a bad cylinder-head gasket or a minute crack in the cylinder wall, and for fragments of bearing metal. Paraffin and a stiff
brush may be used for cleaning the sump and the various filters, but petrol is to be preferred, as it evaporates, so that there is no chance of any being left to contaminate the new oil when the sump is refilled.
Where the cylinder-block is cast in one with the crank-case, the pistons can only be withdrawn after the sump has been dropped and the bottom half of the bigends taken off. The bearing shells are stamped with the numbers of their cylinders, and should be stored carefully with the bolts and their respective shims or thin washers, so that the whole assembly can be replaced exactly as before. The pistons are normally withdrawn from the block in an upward direction, as oil baffles and other obstructions are likely to prevent them being removed downwards. They should then be examined and
decarbonised as already described.
The condition of the bigends should be noted. Correctly fitted ones have a dull, often greenish, sheen, while if they are discoloured or have isolated bright spots, they probably require attention. Taking up bearings is not a job to be tackled by the inexperienced owner, and if they need to be dealt with, one would he well advised to have it done by one of the firms who specialise in sports car tuning.
Big-end bolts sometimes stretch, which can be detected by their threads having a jagged appearance, and if this is the case, they should be replaced. Bolts of hightensile steel are needed for this position, and the makers of the car will have -suitable ones in stock. The nuts should be tightened really firmly, and the rods should have no shake on the crankpins, but should be quite free. Any locking devices must be put back.
Before replacing the pistons, the gaps in the piston rings should be spaced Out evenly, and engine oil should be put on the cylinder walls. No difficulty will he experienced in putting back the sump, but the faces should be clean, and the washer may be coated with L’Hermeticol or a similar jointing contpound if it is found that this was done originally. When putting back the cylinder block, the crankcase should be turned so that two of the pistons are
at top and the rings compressed so that the pistons can enter their bores. There are on the market special collapsible bands which can be pushed over the rings -and which slide down as the pistons are inserted. The block can then be lowered slightly and the other pistons guided in.
Needless to say, a non-reversible pulley tackle is a great convenience in replacing a heavy block.
The cylinder-block holding down bolts need to be tightened down evenly, starting, say, with the end ones diagonally opposite one another and working to the middle. The lower water connections will need to be put back, and in this connection one can recommend the Jubilee radiator clips, with which secure joints can be made even if the water-hose is not an exact fit on the metal stubs. A copper and asbestos gasket is generally used for the cylinder-head joint, and if it has been taken off without being damaged, it may be used again. Even a slight cut made by a screwdriver in prising up the head may weaken it, however, and a new one should be used. These gaskets are put on dry, or sometimes smeared with
grease or oil. Klingerite gaskets, made of a woven material, are now used on many cars with success, while a copper washer is usual on racing cars. These may be used almost indefinitely, but may need annealing by heating over a gas ring and plunging into cold water. Care must be taken to bolt down the cylinder-head carefully, otherwise it may be warped, and the maker’s instruction on them gives specific instructions as to the order in which this should be carried out. After the various water pipes and oil pipes, if any, have been replaced, there only remains to reconnect the camshaft drive, or to put back the push-rods, according to the type of engine. A strong screw-driver to lever up the rockers is indicated in the latter case. The tappet clearances then need to be checked over, and should not need much alteration if
the pushrods are put back in their original positions.
Ball-ended rockers with flats on them, such as were used on the old-type Bentley engines, may be deceptive if the flats are not registering with the valves.
Alter filling up with oil and water, and re-connecting controls, exhaust pipes and other exterior fittings, the engine should be started and run for a few minutes, keeping an eye on the oil-pressure guage in case the pump has become air-locked. The engine should then be stopped, and the cylinder head bolts tightened, and after this has been repeated, the tappets will probably need a final adjustment. Final attention to water and other joints may also be indicated, and this completes the engine overhaul. A further article dealing with the engine accessories and the chassis will be given in next month’s issue.