SOME NOTES ON THE 1 1/2- LITRE ASTON MARTIN
SOME NOTES ON THE 11-LITRE ASTON MARTIN
'These notes, by a reader who is now a Wing-Commander in the R.A.F., although a departure from our more usual tuning notes, will be of interest to all present and prospective Aston-Martin owners, although the advice given is not necessarily that agreed by the makers. The writer has had ample experience of the marque, racing included, after becoming interested through perusal of a MOTOR SPORT road test twelve years ago.—Ed.]
DURING the period from 1929 to 4936, after which the o.h.e. 14-litre Aston Martin went out of production, live models were produeed, the Internatioaal, Standard, Le Mans, Mark II, and Ulster. The first was of separate gearbox construction, with a worm-drive axle and torque tube, and may be readily recognised by the flat radiator and rod-operated brakes. The last three, with -which this article is concerned, have a Vee radiator, engine and gearbox of unit construction, a bevel drive and open propeller-shaft, and cable-operated brakes. They may be distinguished from one another by the &glowing points. The Le Mans (often wrongly referred to as the Mark I) model was pro, dueed in 1933 and 1034, and may be recognised by the oil filter, which has an aluminium cover, and runs the whole length of the offside of the engine. The Mark II and Ulster ears were built between the end of 1934 and 1930, and are recognisable by the Auto Mean oil filter near the front of the engine, and an additional frame cross-member, which is situated between the crankcase and clutch housing. The Mark II also has radiator shutters. The lister model has a higher compression ratio, a camshaft with more overlap, and, uswilly, a two-seater body with the spare wheel very neatly stowed horizontally in the tail. Any car bearing the engine and chassis numbers L.M. followed by a two-figure number is a car built specially for racing. In buying a second-hand car, a test run of at. least fifteen miles should be undertaken, during which the car should be driven fairly hard. If, at the end of this, the oil-pressure has nof fallen below 20 lb./sq. in., the engine is in all probability in good condition. A rough and ready estimate of the mileage of the car may be made from the wear on the gearlever and gate, as if there is appreciable wear on the gate between the top and second speeds, and if the gear lever is worn about half through, a total mileage of about 100,000 is indicated, and, by this mileage, the driver's right heel has generally worn a hole through the floor boards I
The i.e Mans and Mark ll cars have a compression ratio of 7.5 to 1, and it may be wondered how they like " Pool " petrol. The answer is that a pair of Cox Atinos economisers, together with a slight increase in the use of the ignition lever, render them quite tractable, although the fuel consumption increases to about 26 m.p.g., as opposed to 28 on -Cleveland' Disco!, which was found by far the most suitable fuel in peace time. This increase is, at any rate in part, due to the necessity for increased use of the gears. An extension brazed on to the ignitionlever makes for comfort, avoiding the need for removing a hand from the wheel to operate the contml. Retarding the ignitton,timing by means of the vernier adjustment is not recommended, since it will decrease the "saver and increase the consumption.
As regards the performance of the car as a whole, two points stand out, namely, excellent steering and road-holding (particularly in the case of the Ulster model), and retention of tune. The Maximum speed is in excess of 89 m.p.h., at which gait the speedometer of the Le Mans model is, in the writer's experience, fairly accurate, whilst that of the Mark H usually records some 88 m.p.h. Acceleration from zero to 00 m.p.h. in the shortchassis models is of the order of 21 to 23 seconds—not brilliant, but the car is sturdily and somewhat heavily built. The brakes are a rather weak point, being heavy in operation, while it is rot easy to obtain a Tapley Meter reading in excess of 90 per cent. A vacuum-servo motor might help in this respect, and it is the writer's intention to experiment in this direetion. The hand-brake operates on all wheels and greatly assists if used in conjunction with the foot-brake. There is no compensation hi the system, but once adjusted correctly—not a very long job— the brakes require no attention for a long time, other than that of greasing the cables, which should be done regularly. About once a year it is advisable to remove the brake drums and shoes and to clean and oil the shoe-fulcrums with thin oil, used very sparingly. This takes less than an hour, and is Well worth doing.
Here are some jobs which have been tried and found satisfactory, nearly all of them within the scope of the average owner of the type who does his own maintenance. The first two are war-time makeshifts, intended to avoid or postpone extensive overhauls. If it is found that the oil-pressure becomes unpleasantly low when the car is driven bard, and that adjustment of the relief valve affords no improvement, the usual cause is wear in the journal and big-end bearings, and in the pressure oil-pump. It will be recalled that the hibrication is on the dry-sump principle, and both pressure and scavenge pumps are identical except that the former is 1 in. and the latter 1Ain. long. Obtain a new scavenge pump-ease and new gears, and cut these down to I in. in length. The gears do not need softening, but care must be taken to ensure that both case and gears are cut absolutely .square, and to make a good face-joint between the case and end cover. There should be a clearance of .001 in. between the end cover and the spur gears. The existing studs are long enough to accommodate the extra length. of casing, and the scavenge pump has sufficient excess capacity to deal with the greater -oil-flow. A consequence of this greater flow may be oil finding its way past the front main bearing into the dynamo, which can be overcome by drilling a At-in. drain-hole at the bottom of the dynamo-casing, immediately in front of its flange. It will be necessary to adjust the relief-valve after fitting the new pump, setting it to give it pressure of 30 lb./sq. in. when the 'engine is thoroughly warm. If the valves are old, repeated grindingin may have made the edge of the heads sharp, and this is liable to cause pre-ignition in the case of the exhaust valves. This sharp edge should be skimmed off, removing as little metal as possible. The valves are of ValchrOme steel and should not be roughly handled, as the stems may become bent. The writer once tried IC.E.905 valves on a car which was being prepared for racing, but increased pinking was noticeable, and he was subsequently told by Ileaclli that, in a bench test, the standard valves ran at a temperature
75° C. below that of the K.J.ones.
'The flywheel weighs 45 lb., and from 12 to 15 lb. can be removed, resulting in slightly quicker upward changes and a little better acceleration. Here again, care must be taken to engine that the flywheel is not weakened, and that the balance is not upset. The weight Must be removed from the front face, since the clutch is mounted on the rear one. However, since much dismantling is necessary before the flywheel can be removed, and since the results are not very pronounced, this job is not worth the trouble of doing unless the clutch has to be dismantled at sonic time, and this is unlikely unless the engine is being removed from the chassis. Power-output can be improved at the expense a economy by substituting 36 mm. carburetters for the normal 80 mm. pair (a new balance-pipe will he necessary) and using a T.T. camshaft, which has 41° of overlap as opposed to the 190 of the standard shaft, whilst the use of 9 to 1 compression-ratio pistons will improve both economy and power-output in a most marked manner, but is imprac-,, ticable on Pool spirit.
i.e Maus models were equipped with a fibre timing pinion, for quietness. This is liable to fail, and it is most advisable to replace it by the later steel pinion. Since the failure invariably involves bent valves, and sometimes further damage to the engine, it is wise to effect the change before the teeth strip. The wheel is quite easily reached if the radiator is removed, but it should be noted that the bottom of the timing-cover is flanged and that two bolts below the front of the sump screw into this flange. These bolts must be removed before the tinting cover will come away. Here are some items of general information. Champion R.1 plugs are most satisfactory for normal use. This grade is several degrees harder than the plug recommended in the Aston Martin handbook, but it is the type recommended by Messrs. Champion, and unless the car is using oil at a phenomenal rate, no oilingup trouble will occur, and erosion of the points takes place more slowly. The plug gaps should not be allowed to exceed .015 in. or the engine will missfire when the throttle is opened ; .012 in. is the best figure. This point should be watched when new plugs arc fitted, as the gaps of these are very frequently much greater
than this when the plugs are sent out. The writer has seen many people who should know better attempting to adjust the gaps of this and similar types of Champion plug by bending the central electrodes. Even if the insulator does not crack at the time, there is a very serious risk of splinters chipping off after the plug is installed in the engine, and such splinters do a mighty lot of no good! If the gap is too large, the earth electrode should be tapped inwards with the aid of a line pin-punch. The normal oilpressure for all three models is 30 11,/ sq. in., and 20 lb./sq. in. should be regt)rded as the minimtun safe: pressure at normal engine-speeds. Below 2,000 r.p.m. the pressure is sure to fall off when the car is old, and when idling the pressure ulay lie only two or three pounds. The bore and stroke are 69.3 by 99 mm., giving a capacity of 1,495 c.c., the exact bore being 2.728 in. and not 2.73 in. as quoted in the catalogues of some piston manufacturers. Tlie correct valveclearances, at running temperatures, are : inlet .006 in., exhaust .008 in., and these should be measured with the blade or the feeler between the valve and the rocker, not between the cam and the rocker. With the T.T. camshaft, an extra .003 in. on each valve is necessary. Both top dead centres are marked on the flywheel, the pointer being on the near side, arid if the flywheel is ever removed, it must in consecptenee be replaced in the same position relative to the crankshaft. One inch of arc on the flywheel rim subtends an angle of 0.6', and the valve timing, Measured on the rim, is : standard C11111 shaft, inlet opens in. bel..01:e T.D.C.,
exhaust closes l in. after ; T.T.
camshaft, inlet opens 2 in. before T.D.C., exhaust closes 21 in. after T.D.C. The standard ignition timing is with the points just breaking at T.D.C. with the magneto luny retarded.
When replacing the valve rocker-plate on the head, ensure that there is a paper washer on the machined face having the front dowel. Here there is an oil-duct, in the underside of the rocker-plate, for lubricating the timing-chain, and if the washer is omitted there will be a serious lack of oil-pressure when the engine is warm. Before removing the valve-spring retaining caps, but after removing the lock-nuts, measure the length of valvestem projecting, and when replacing the caps, screw them down the same distance. If in any doubt, tend to leave slightly less stem exposed, because the caps can easily be screwed down if necessary, but, owing to the jamming action of the springs, it is sometimes difficult to unscrew them. If the caps are screwed down either too much or too little, it will not be possible to obtain the correct valve clearance. Cylinder-head gaskets are solid copper and hardly ever need replacing, but should be annealed each time they zi.re removed. They are available in two thicknesses, .030 in. and .055 in. When fitting the head, the nuts should be pulled down" really tight, because they cannot be further tightened 'without reinoving the rocker-plate. If for any reason the cylinder-head studs are removed from the block, it is essential to ensure that the stud close to the valve-gear oil-duet is
not left too long on being replaced, otherwise it will foul the rocker-plate at this point, causing a very bad oil-leak, and there is a risk of the plate being fractured when its nuts are tightened down.
Castor-oil is recommended by the makers for both gearbox and back axle, and the car runs appreciably more freely if it is used. Castor-oil is not, however, recommended for the engine. The standard axle ratio is 4.66 to 1, the lower gears being, in the cat-, of the Le Mans : 14, 8.7, and 5.9 to 1, and in the ease of the Mark II: 12.9, 8.1, ail(' 5.9 to 1. Alternative axle ratios are 4.25 and 4.4 to 1, the latter having straight-tooth bevels.
The Le Mans model had two Autopulse fuel pumps mounted close to the back axle. These pumps are extraordinarily reliable and need little attention, but if necessary they can be reached through a trap, just above them. This trap is in the floorboards, and is so well concealed that it may easily pass unnoticed. The engine oil-tank holds 21', gallons in the ease of the Le Maus cars and 2.9 gallons on the Ulster and Mark II models. The correct oil-level is one Melt below the filler-neck. It is inadvisable to circulate flushing oil through the system because a certain amount will remain in the pipelines, filter, etc., and it will dilute the fresh oil. The radiators of all three models 8;lt gallons of water. These large tonounts of oil and water are ideal for fast long-distance journeys, for which use the car is intended and is at its best. The drawback is that some miles are required for proper warming-up, and in these days of restricted me and short journeys, this leads to oil-dilution-particularly with Pool petrol-and worn cylinder-bores, unless steps are taken to ensure that the proper running temperatures are speedily reached. The writer uses a thick muff which covers the entire bonnet and lower half of the radiator, and which is retained
by snap fasteners. This remains fitted except in the very warmes weather, and beAdes ensuring rapid warming-up, will keep the engine warm for hours in the coldest weather. (The top half of the radiator is, of course, covered when the car is standing.) When running,, the temperature is kept at between 80° and 85° C by means of the shutters. In conclusion, several people have
fitted superchargers to the 1 k-litre Aston Martin. Different types of supercharger have been tried, at maximum pressures varying from 7 to 15 linjsq. in. with, of course,. the Ile cessary reduction of compression ratio, butt as far as the writer has been able to ascertain, none of them has been really successful, and the marque for some reason does not seem to lend itself to high density induction.