The De Havilland-M.G. Sprint Special
Interest has been lent to this season's sprint contests by the appearance in some of…
WINTER WORK IN THE GARAGE (Continued from the January issue of MOTOR SPORT).
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 engine accessories and components should next receive attention. A beginning may be conveniently made on the carburetters and the fuel feed system. If the engine has been giving previous to the overhaul a performance and petrol consumption normal for the car in which it has been fitted, there is no point in experimenting with different chokes and jets. The instrument should, however, be dismantled, and any sand, water or other foreign bodies carefully removed from the bottom of the float chamber and the jet passages, and also from the ‘small
filter often found in the union at the top of the float chamber. Punctured floats are rare nowadays, but may be detected by shaking them. If the float should have a leak, the petrol may be driven off by heating in very hot water. The petrol vapour escaping will show as a stream of bubbles, and the puncture may be repaired with a careful application of solder.
When tuning the carburetter for speed or other special work, the advice of the competition manager of the manufacturer should be sought, as he will probably have had experience on other cars of the same make and type. The principle is roughly that one wants the biggest possible choke for all-out speed, but a smaller one is needed at low speeds for good acceleration, so that a compromise must be effected. The jet size will be a little bigger than that Which gives maximum power, in order to keep the plugs cool.
The S.U. carburetter, which is one of the most popular on British sports cars, uses a large jet which hardly ever needs changing, the metering at various points In the throttle opening being effected by means of a tapered needle. Engine suction raises the piston, the bottom end of which acts as a choke, while needles of varying contour allow the setting to be changed to suit all conditions. For a richer setting over all the range, the jet may be lowered by means of the hand control, and the new position made permanent by screwing down the nut at the bottom of the jet chamber to meet it. The simplest method of fuel feed is by pressure, and the only points which require attention are the washer on the filler
cap, which may need replacing if it does not hold its pressure, and the pump washer, which should be greased occasionally. The tightness of the pipe-lines should be checked and if there are any sections of flexible piping these should be examined for signs of perishing. Pressure feed finds out weaknesses in carburetter float needles, and if they are deeply ridged, they should be replaced, as grinding them in to form a new face is not satisfactory.
Vacuum feed is seldom found nowadays, partly owing to its habit of drying up after a long burst of full throttle. Water and sediment should be drawn off through the drain cock at the bottom of the tank, and the suction pipe from the induction system to the tank should be kept tight. If a suction windscreen-wiper is fitted, and its pipe leaks this will materially reduce the efficiency of the Autovac.
Types of Fuel Pumps.
The S.1′ Petrolift is a simple form of electric pump which seldom requires attention, but grit occasionally gets into the centre tube and causes one or both of the plungers to stick. The top one can be withdrawn on raising the lid, while the bottom one can be reached after removing the filter The centre tube should then be wiped out with clean rag. The new L. Type 5.15. pumps are much more compact and exert a positive lift instead of gravity to feed the carburetter. They should be free from trouble, and any derangements are dealt with thoroughly in the instruction book.
The Autopulse, another popular electric pump, employs a thin copper diaphragm which sometimes splits. If fuel drips from the instrument, and the pipe unions are tight, it should at once be returned for servicing, as otherwise there is likely to be an internal explosion, when the mechanism will cease to operate. The A.C. mechanical pump is deservedly popular, but on the earlier types
the connecting linkage between the operating lever and the diaphragm sometimes developed excessive play, while the return spring occasionally broke on high-revving engines. If petrol starvation has been suspected, and the pipe lines are all tight and clean, these two points should be checked over.
The magneto should next be dealt with. First see that the carbon brush which picks up current from the slip-ring is of ample length to make good contact, and that the spring has sufficient tension to hold
the brush up to its work. A piece of soft rag wrapped round a pencil may be used to remove carbon dust.
The rocker arm on the contact breaker must be free on its bush, and the points should be free from pitting, and should butt square when forced together by the cam ring. Slight pitting may be removed with careful use of the magneto file, but a badly burnt appearance points to a defective condenser. Turning the engine till the heel of the rocker arm is fully raised by the cam, the gap should be set to the distance shown on the guage on the magneto spanner.
A jump-spark distributor requires no attention unless .the revolving finger is badly burnt. Where a carbon-brush distributor is used, the fibre between the segments is liable to be covered with a film of carbon. On a new instrument this may often be removed with petrol and a rag, but as the track gets rougher, judicious use of emery paper will be required. Naturally the rougher the track becomes, the more carbon will be scraped off, so the need for careful treatment will be appreciated. The carbon brush found at the end of the distributor shaft should be inspected, and also the one at the back of the contact breaker.
If an oil-hole is provided on the magneto two or three drops of light oil should be used, and a trace of vaseline on the camring. In a coil ignition set the coil and the distributor are of course two separate units, but the remarks about the distributor and the gap-setting are equally applicable. In order to reduce the speed at which the contact breaker operates (225 times per second on a six-cylinder
engine running at 4,500 r.p.m.) it is quite usual to have two of these mechanisms working on a three lobe cam. Unless the contact-breakers open exactly at an interval of 180 degrees to one another, much power will be lost, and unless the owner is prepared to go to some trouble to get the setting exactly right it is worth paying a visit to a competent service station at least every 5,000 miles to have it checked up. The same applies to those ignition systems in which the advance and retard mechanism is automatic, controlled by weights and springs.
The voltage passing through the coil does not rise as in the case of the magneto, so that its efficiency falls off the greater number of sparks it has to produce per minute, and performance is often materially improved by fitting the magnetos produced by Scintilla or B.T.H., which are interchangable with the coil distributor.
Sparking plugs deteriorate after a season’s strenuous use, and even if the points are not burnt away a deposit of film of low insulating properties forms on the porcelain or mica. A set of new plugs of the correct grade should be put in after the overhaul, with the appropriate gaps of .018 for magneto ignition and .028 for coil. The high-tension leads should also be replaced if the rubber is perishing, or if they have been much in contact with oil and water. and
Battery and Dynamo.
The electric system is of ever increasing importance on the modern car, but can be maintained at a good pitch of efficiency without much difficulty. The dynamo should be inspected to see that the brushes are all free in their guides, and are pressed into firm contact with the commutator by their springs. The commutator should be cleaned with a rag soaked in petrol, and the spaces between the segments cleared of carbon with a blunt pen-knife blade. The leads should all be tight, and the grease cup, if one is fitted, used sparingly but regularly. The starter may also require to be cleaned. The bendix drive should be washed with petrol and dried with a clean rag, for oil on this part will cause the travelling pinion to stick on its thread. A back-fire sometimes breaks the cushion spring at the end of the shaft, and this or a bent shaft will prevent the starter from working properly. That hard working but often neglected accessory the battery, should have each
cell tested with a syringe hydrometer, and if the readings show that it is low, it should be charged at a service station. An individual cell with a low reading may mean an internal short-circuit caused by a piece of one of the plates coming loose due to vibration, and if the method of securing the battery is not a positive one it is worth while having two upright screws secured to the battery crate with a cross-piece to hold the accumulator in position. If one cell in a battery fails, it can be replaced for a small sum at the battery maker’s service station.
If the battery has been in use for a year or two, it may be wise to have the acid changed, otherwise it should merely be “topped up” with distilled water.
Water Pump and Transmission.
Oil and water ways are the only remaining things which require attention on the engine. External oil cleaners or filters should be dismantled and cleaned out, and a new filter unit put into to the type which use a felt strainer. The outside of oil-coolers, such as are fitted to the bottom of the radiators of Hornet Specials, should be cleared of mud and dirt to restore their radiating efficiency.
The water pump is sometimes the Achilles’ heel of the modern engine, but the fault more often lies with the owner, who does not maintain a proper supply of lubricant, with consequent wear of the pump shaft. If a leak occurs when there is plenty of grease in the pump gland, there is usually a nut for further compressing the packing, while if this adjustment fails, the pump will need to come off for the packing to be replaced. It should be noted that” any old grease” will as a rule not stand up to the high temperature of sports car cooling water, and special compounds, which usually contain tallow, are required. As has already been mentioned, Jubilee clips are particularly valuable watertight hose joints.
The dry-plate clutch, which is almost universal in England, has little in it to get out of order. As the linings wear, however, the pedal comes further up, so that in time it may touch the floor boards at the end of its travel, and put pressure on the clutch race, apart from causing actual slip. The position of the clutch lever must be altered so that at the end of its travel it is clear of the boards. The clutch lining only needs renewal when this adjustment can no longer be made, while clutch springs, if of sufficient strength in the first place should last for several seasons. The lubrication of the clutch race and of the pedal shaft should not be overlooked.
The gear-box should be drained, preferably after the lubricant has been stirred up after a run on the road, and the sludge flushed out with thin warm oil or paraffin. The correct grade of gear-oil should be used to replenish, and it is worth noting that the makers sometimes recommend the use of a lighter grade during the winter. If the universal joints are of the mechanical type, they should be refilled with heavy oil or special non-separating grease, according to the design, while fabric joints should be replaced if showing signs of wear.
Attention to the back-axle.
Like the gear-box, the back-axle is best drained and refilled after a run has thinned the lubricant. The filling plate is usually placed in a position such that the casing cannot be overfilled, but it is just as important to see that it is filled as far as it appears to be, and the oil should be circulated by jacking up one of the rear wheels and pulling round by hand to make sure that it has reached all parts of the casing. To make pouring easier, the oil may be warmed by leaving the tin half submerged in a bucket of hot water for a few minutes.
If the brakes have been functioning properly, and have been recently re-lined, it should not be necessary to disturb them, but otherwise the brake drums should be removed and the linings examined. With Rudge hubs the drums may sometimes need to be removed with the hub, by slacking off the nut on the axle, and striking the end of the latter with a hammer and a brass punch, taking care not to damage the thread. The hub and the drum may also be tapped with a mallet.
A wheel puller is however the safest resort If a hub of any type has to be removed. Quite often of course the drum is simply bolted to a flang on the hub and can be easily taken off. If the linings are worn down nearly to the rivets, they should be renewed. In many cases it is possible to get linings die-pressed and ready drilled, in which case they merely have to be secured to the shoes, which is done with aluminium or copper rivets. If the brake is not a stock type, the lining will have to be fitted from a strip of fabric of the right width. It should be secured starting at one end and working to the other, and the holes
should be well countersunk to prevent the rivets scoring the drum. The lining should be sloped off with a file at each end to prevent chattering as the brakes are applied.
Glazed linings should be roughed up with a file, while those which are oily may be soaked in petrol which is then lighted. Oil in the brake-drums means either that the brake shafts have received too much oil, or in the case of the rear set, that the back axle has been over-filled, or that the felt washers which retain the oil need renewing. A trace of grease should be used on the brake cams.
If the drums are slightly scored they may be skimmed up in a lathe, but if the cuts are deep, new drums are to be preferred, since brake-drums are already rather thin on many modern cars, and replacements are not expensive. Alternately the old drums may be fitted with Laystall hard steel liners which are practically indistructable.
Springs and Shock Absorbers.
Scoring is usually caused by projecting rivets, or by using racing lining, such as Ferodo MZ on soft low-carbon drums. The remedy in each case is obvious.
Before replacing the wheels the hubs should receive a small quantity of grease to prevent the wheels sticking on the taper, and this will also be a convenient time for going over the wheels for loose spokes. Nothing need be said about adjusting the brakes, but if new linings have been fitted the adjustment may need taking up once or twice before the fabric beds down. Jacking up the chassis will allow the leaves of the road springs to separate, and graphite grease can be put between them
with a putty knife. Spraying with penetrating oil is an easier but less lasting method of dealing with them. Spring gaiters are not used much nowadays, but it is worth while removing them if fitted to see if there any broken leaves. Hartford shock-absorbers may be taken to pieces, the discs cleaned with petrol and slightly greased before re-assembling. If they seize solid they will snap the brackets.
The Lighting System.
All grease or oil points should then be gone over, and if the nipples are blocked, taken off and cleared with a delightful tool called the ” Biffit ” in which a hammer blow forces lubricant from a miniature grease-gun.
The lamps and their connections should be overhauled, and if any of the bulbs show discolour ation, they should be replaced before they fail altogether. The charging rate of the dynamo should exceed by at least one ampere the consumption of the lamps, and if it does not do so, either the rate should be increased by moving the third or regulating brush of the dynamo, or if the latter has reached its maximum rating, bulbs of lower consumption must be used.
If a lamp glass cracks across, it should be replaced at once, otherwise moisture and road dirt will reach the reflectors, which will have to be sent back to the manufacturers for re-polishing. Some lamp reflectors have a film of transparent varnish and may be cleaned with care using an ordinary soft cloth, but the more expensive ones are usually
delicate, and only silk may be used for wiping them.
Nothing now remains except the instruments and the coachwork. Speedometer cables should be taken off and lubricated with oil or light grease according to the maker’s recommendation. U tube petrol guages such as the Hobson occasionally go wrong, but the very complete instructions which can be obtained will enable any fault to be rectified. Pressure guages can often be perusaded to return to the zero mark by judicious
bending of the internal curved tube. Radiator thermometers cease to function when the liquid escapes from the pipe to the radiator, and must then be sent back to the makers. The same applies to clocks and ammeters. As to the coachwork, prevention is better than cure. If a friend can be obtained to jump up and down on the running boards, the owner can usually trace loose wings and tighten them up, or replace rusted-up bolts. If the front wing assembly is insecure, two upright tubes bolted to the chassis and ending in split lugs to take the cross-tube supporting the lamps will take the place of a
multitude of wire stays and other fixings, without detracting from the frontal appearance of the car.
Last and not least, a touch of paint supplied to the wings will often prevent the fatal patch of rust which makes replacement necessary.
Any general article dealing with overhauling the car must needs be incomplete, but if the owner can spare the time and trouble to attend to the points mentioned, the chances of an unexpected breakdown or premature wear will be greatly reduced, while his interest in the car will be very greatly increased by a practical knowledge of the details of its mechanism.
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