TUNING M.G. CARS
SOME NOTES by W. E. WILKINSON (In an Interview)
Everyone who has anything to do with sports or even touring cars knows that no two cars, apparently identical in every respect, give the same performance. Small variations in valve tinting, the casting of the cylinder-head, the fit of the bearings and pistons, all these can affect the ultimate result, though it is almost impossible to detect them until the car is fully run in and tried against the stop-watch. Obviously tuning is of little account unless the chassis is a good rue, and this is a point which makes the tuning of M.G. cars particularly worth while. The lay-out of the chassis, brakes and so forth has been determined as a result of racing experience and so there is a margin ample to deal with any extra speed which may be obtained, and it also happens that for a small amount, say .£5 to £10, a useful and certain improvement Of performance can be expected in
The first car to be considered is obviously the popular ” P ” type with its three-bearing four-cylinder engine, virtually identical with the unit used an the ” ” and ” R ” type cars and thus capable of a substantial increase in power without fear of damage.
Before starting work it is advisable that the engine should be run in, so as to be able to detect the improvements in performance which are being made, though of course there is nothing in the tuning which could not be done to a new engine. We usually start with checking the camshaft timing, making sure that the inlet valves open, as they should, 15 degrees before top dead centre. Sometimes the keyway is machined a fraction out of position, and in this case the alteration in timing has to be rectified by making a new key. In the. same way the ignition timing must be checked, the correct setting being A-inch before t.d.c. With the ignition fully advanced. If the setting is wrong, and particularly if the owner has been trying a little ” private ” tuning, the error is nearly always in the direction of too much advance, and an improvement of 2 m.p.h. with smoother running often follows simply through attention to this point.
The next thing to be decided is the compression ratio desired. The standard ratio is 6 to 1 and this can be taken as high as 8.5 to 1 without any major alterations, but in this case the engine ic ill re-quire a mixture of 50 per cent. straight or ethyl petrol and 50 per cent. benzol. Not everyone is prepared to go to the. trouble of buying benzol however, so generally we are content with removing A-inch of metal from the head and using a thin gasket. This gives a -compression ratio of about 7 to 1 and an increase of speed of 3-5 m.p.h., while the engine .still runs .smoothly on standard fuels.
The next move is to grind out and polish ports, and to make sure that the
Mr. Wilkinson has had a varied experience of sports and racing cars. Some years ago he was head tuner to Captain Eyston and accompanied him and the late Count Comfrari on their Maseratis in the Double Twelve, the Irish Grand Prix and the 7′. 7. lIe acted as spare driver to Mr. R. E. Tongue in the 1934 500 miles race, finishing fourth on an M.G. Magnetic. He is now racing manager of the Bellevue Garage. ED.
A dynamometer is of the greatest use in checking the effect of small adjustments. This one has just been installed at Me Bellevue Garage.
extra as a result of providing a free passage for the incoming mixture. Triple valve springs we also find useful in getting the utmost out of the ” P ” type engine. The tension is very little
greater than that of double springs, but valve bounce is nevertheless avoided since their period is well above any revs. which the engine will reach. The standard engine components have a sufficient margin of safety to stand the extra power produced by these altera tions, but sparking plugs -iaving a higher heat-resistance need to be used, the
14 min. K.L.G. L.K.1.’s proving satisfactory. With the 7.5 to 1 compression it is also advisable to fit valves of K. steel.
All these attentions cost comparatively little, and a car which previously May have had a maximum of anything between 70 and 78 m.p.h. should now be capable of a genuine 80. If you are an enthusiast with a good supply of ready cash there are other things which add to the car’s efficiency, though naturally as this is raised the extra m.p.h. become proportionately difficult to obtain.
One thing which helps in many cases is to have the bearings eased. It is difficult to forecast exactly how much bearings are going to bed down with running in, and occasionally we find them still tight after several thousand miles. A clearance of two-thousandths on main and big-end bearings May actually prolong the life of the engine, since, the crankshaft expands just as surely as the pistons or the cylinder block. Another thing necessary to ensurethat the engine is giving its best is to make certain that the Connecting rods are running parallel with the bores, while those who wish to take part in speed trials may find it worth having the compression raised to 10 to 1 and running on alcohol fuel. Most people with the ” P ” type tar naturally do not centemplate doing anything as drastic as that and for ordinary events such as reliability and speed trials the 7 or the 8.5 compression prov ides q tiit e enough power.
Nothing has so far been said about the chassis. Very little. is required in this direction beyond seeing that the brakes and wheel-bearings are lr in all positions, and if high-speed work is contemplated to bind the road springs with insulating tape and then cord, with final layer of tape to make a neat job. It is assumed of course that spring slides, joints and other vital parts are in good condition. There are still, of course, a great numIm:r of the earlier ” J ” type Midgets in regular use for trials and road work. The same treatment suggested for the ” P ” type may also be successfully employed on the earlier cars but the two., bearing crankshaft puts a limit to the power which can safely be obtained, and we seldom raise the compression above. 7 to 1.. This applies even more strongly to the supercharged Montfliery. As an experiment we had a specially balanced Laystall crankshaft made for one of these cars at a cost of £25 and ran it successfully through an entire season without
trouble, and if anyone is thinking of using one of these cars regularly in competitions, I strongly advise obtaining one of these.
Before leaving the Midget it might be well to say something about petrol consumption. The consumption of the standard car is about 39 m.p.g. Raising the compression to 7 to 1 improves the figures slightly, and even On 8.5, where slightly richer needles are required in the carburetters, the increase in fuel consumption is negligible.
The ” 1.1′ type Magna gave less scope for tuning than most of the later models, as the engine was rather small for the size of the chassis and required to run at high revs, before much power was produced. We have had quite good results with one of these running with an 8.5 to 1 compression, but a more successful way of tackling the problem was found in fitting a small Marshall supercharger blowing at 5 lbs. A larger and more efficient water pump Was also found of advantage.
The last type Of sports M.G. I deal with is the “N ” type Magnette, which is perhaps the most responsive to simple treatment. The engine is dealt with in exactly the same way as that of the ” P ” type Midget, and the compression may safely be raised to 8.5 to 1. The cars driven by Mr. K. D. and Mr. D. G. Evans have been prepared in his way and we have had excellent results with them, running throughout a season of trials without even dropping the sumps. 75 horse-power is developed at 6,500 r.p.m. V2ives, pistons, connecting-rods and other components are all standard, but the clutch springs have been strengthened, and the gear-box pinions originally fitted in the old ” j ” type Midgets are used, as the standard ratios are rather too low for trials work. Cylinderhead gaskets are dispensed with, the heads being checked on a surface plate and then lapped on to the block.
With trials ratios the all-out speed is 85 m.p.h. though another 5 m.p.h. can be obtained with a higher back-axle. The T.T.-type car which is capable of 95 m.p.h. is identical except for a different camshaft, which gives more overlap, and larger carburetters. The higher speed is obtained, of course at the cost of power low down. At the end of the racing season we experimented with a Magnette on which the compression ratio was raised to 9.5
to 1. Alcohol fuel naturally was needed. The car finished first in a Mountain Race and a close third in an outer circuit race, the best lap speed in the latter race being 104.19 m.p.h. With regard to the racing cars, the supercharged Magnette and ” Q and ” R ” type Midgets, any modifications we have carried out have been of a minor nature, most of the attention, as usually happens in cars of this type, being given to seeing that every part is free and a good fit. The camshaft on the Magnette
which only gives 15 degrees overlap can be changed with advantage for one giving an overlap of 25 to 35 degrees. As regards the chassis considerable weight can be saved by fitting a light body and Smaller batteries, while road-holding is improved by removing two leaves from the rear springs. The wonderful little engines fitted to the ” Q ” and ” R ” Midgets are almost identical. They can be revved safely to 7,800 r.p.m. and one we had on the bench the other day gave 116.6 h.p. at 7,500 r.p.m. Beyond rather ticklish jobs such as lightening the rockers and providing special valve cotters, nothing out of the Ordinary is needed on them, but we have made some successful experiments with a special cylinder head in which the sparking plugs screw into masked openings. There are no shoulders on the bodies of the special 14 mm. plugs, the copper gaskets being sandwiched in between the bottom of the
plugs and the metal of the cylinder head. This method of construction keeps the plugs cool and reduces the size of the opening into the combustion chambers. Our racing this season concluded with an attempt by Mr. Kenneth Evans on the 750 c.c. Mountain record. Previous attempts we had made showed that though the power developed by the ” R ” type Midget was quite sufficient to give us the record, the violent braking called for at the corners rendered the brakes almost inoperative after a few
laps. This we attributed to the fact that the brake drums were shielded from the air -stream and also the fact that the drums and shoes were both made of the same material, so that the heat did not flow away from the linings. Fitting windscoops on the back-plates and fins on the drums completely overcame this trouble, and a few days before the track closed, Mr. Evans took the record at 75.24 m.p.h., a satisfactory finish to a season in which cars tuned at the Bellevue Garage scored 45 awards in racing events and 36 in reliability trials. Racing nowadays is a strenuous business, but for the amateur with a small amount of money to spend, plenty of amusement can still be had from taking part in the smaller speed trials and the Club events at Brooklands, and next season we expect to be busier than ever preparing M.G. and other makes of car for events of this kind.