Some notes on the Brescia Bugatti

[Although very few Brescia Bugattis are left intact, so many people enthuse over them, so many would-be Bugatti owners intend to start with this model, and they are so typical of high-efficiency cars in general, that these notes by J.A. Fawcett are of considerable interest. – Ed.]

As long ago as 1910 M. Ettore Bugatti had designed his Type 13 eight-valve four-cylinder of 65 x 150 mm. and capable of 60 m.p.h. This was followed in 1914 by his sixteen-valve model (68 x 100 mm.), with plain bronze bearings. The racing version was very successful in 1920-22.

The earlier models developed 30 h.p. approximately at 3,000 r.p.m. on a 5.5 to 1 compression ratio, the car weighing about 11 cwt. with short wheelbase, and 3 to 1 top gear, being capable of 80 m.p.h. A later development by Leon Cushman with 8 to 1 compression ratio did over 90 m.p.h.

The standard car (produced up to 1923) weighed about 15 cwt. and with 3.46 to 1 top gear was capable of about 65 m.p.h.; third gear gave up to 60 m.p.h. – but the yowl!!

The next development was the Brescia and Modified Brescia, produced up to 1926. These had the 69 x 100 mm., ball-bearing engines, the only difference between the two being twin magnetos firing eight plugs for the Full Brescia. which was usually turned out as a short wheelbase racing job, against a single, forward-set magneto of the Brescia. These notes deal with the Modified Brescia produced from 1924 to 1926, the latter models having f.w.b. This engine had an improved disc type built-up crankshaft and an improved lubrication system and, with a compression ratio of 5.8 to 1, developed about 48 b.h.p. The gearbox was also improved by the use of wider gear wheels and silent constant-mesh gears, making it reasonably quiet. There is no doubt that a good example of this car, driven and serviced intelligently, is a very desirable piece of property. Unfortunately, they often get into the hands of incapable people and get “caned” to death.

The car was designed for a definite purpose, i.e., high-speed cruising (60 m.p.h.) with reliability and economy. It was guaranteed to do 75 m.p.h. in top gear. 65 m.p.h. in third gear and to give 40 m.p.g. at “touring speeds” – add to this a comparatively low r.p.m. limit (3,800 r.p.m.) giving reliability and one has a performance not out of date sixteen years later.

The gear ratios employed have a good deal to do with the above performance. The standard axle ratio of 13 x 45 gives 3.46, 4.5, 6.39 and 10.10 to 1, and with 720 x 120 mm. beaded edge tyres the road speeds at 1,000 r.p.m. are, respectively, 23, 17 1/2, 12 and 8 m.p.h. Therefore a cruising speed of 60 m.p.h. equals 2,600 r.p.m., and, of course, it is impossible to over-rev, on top gear. Actually a good model will cruise at 3,000 r.p.m. on about two-thirds throttle. Experience with this model indicates a few hints and modifications, bearing in mind the fact that no attempt has been made in tuning for speed alone – in fact, mechanical soundness, quiet running and flexibility have as far as possible been the chief objects, although acceleration has been improved. All sixteen-valvers are now old, but if the main bearings and valve seats are sound they can be rebuilt successfully – if not, it will be impracticable to make a good job. Over-revving, especially from cold, causes cracked valve seats, and a replacement block in sound condition will be hard to obtain.

Lubrication causes a certain amount of difficulty. The gear-type pump driven from the camshaft draws oil via a long pipe from the sump. It is usually necessary to prime the pump after the engine has stood for some weeks (a screw is provided on the inlet side of pump for this purpose). Should the pump fail to pick up on normal occasions, it is due to air being drawn in via the oil unions or via a worn pump driving shaft bush. The oil pressure is about 1 kilo. per sq. cm. at running temperature. It registers low when cold (about 0.5 kilo.) and increases on warming up. It is sound practice not to “step on it” until the pressure becomes normal. The pressure can be adjusted via the rear main-bearing oil jet (enlarging lowers it and vice versa). If the pressure rises unduly it indicates a choked jet in the gallery pipe and should be investigated without delay. A line is scribed on the heads of the jets, and this line must register directly fore and aft.

The camshaft and tappets are lubricated via a feed from the back of the pump, which can be cheeked by removing a pin-spanner disc. An overflow pipe is supposed to keep up the level in the cam casing. but this is often removed by duff mechanics as a cure for over-oiling.

A useful idea for preventing oil from passing down the valve guides is to obtain shrouded valve spring caps from the exhaust valves of the 2-litre straight eight car, which are of the same size. In spite of all precautions, oiling up will occur when the oil gets old and loses its viscosity. The remedy is to drain and refill with fresh oil. In the old days one used Castrol “R” which had high viscosity, but was at a disadvantage in cold weather, as it never really got circulating on short journeys (the engine runs very cool) and this starves the valve gear. A low-priced oil, such as Pratt’s “Snowdrift” (4/8 pre-war) plus colloidal graphite gives satisfactory results. Put 3 quarts in and drain off when viscosity is too low (indicated by blue smoke after idling).

Valve Tuning. – There is a little overlap and it is usual to set this one-third on the inlet, side and two-thirds on the exhaust side.

Tappet Clearance. – Standard clearance is 8 thou. inlet and 10 thou, exhaust; 10 and 15 thou. respectively is O.K. with standard valve springs (with which valve bounce starts at about 3,700 r.p.m.). Extra strong springs are not advisable for ordinary work, as they cause excessive wear on the tappets. Tappet shims used to be available from the makers in 0.002″, 0.004″ and 0.010″ sizes, but these can be pressed out of mild steel sheeting.

Ignition Tuning. – Fully advanced, not more than 35˚ before t.d.c. More advance is had for the engine bearings.

Compression Ratio. – Standard 5.8 to 1; 6.8 to 1 can be used with “Pool” and 7.5 to 1 on Discol (about 5 mm. increase in piston crown), which is about the limit for ordinary work.

Ignition and Carburation. – A coil ignition set (ex-Morris Cowley conversion set) gives better slow running and a Solex carburetter gives good pick-up without flat spots (setting 23 mm. choke, 115 x 51 jet).

Plugs. – Champion 17 or Lodge C.U. (lorry type), detachable for cleaning, are best, owing to oil. The gap should be 0.015″.

Clutch. – Correct adjustment and care of the clutch is absolutely essential if the finer points of gear changing, etc., are to be enjoyed. All lost motion should be eliminated. The thrust bearing and housing are a source of this and are better replaced by a deep-groove ball bearing in a suitable housing or possibly with a unit from a Type 40. Adjustment is by a screwed ring, which can be turned by a tommy bar when clutch pedal is depressed. When all this adjustment is taken up, longer pins can be used. The last bit of movement of the pedal should “feel” the pins forcing the clutch plates together and the toggle arms should be in line. When adjusted correctly it should be possible to engage first gear from rest with very little noise. When the clutch sticks wash it out with paraffin and squirt in some graphited penetrating oil. The clutch square is apt to wear ridged and is better ground off, and when worn a good deal, chatter is observed on “tick over,” but is not serious, providing clutch action is good. To assist gear changing the gear lever selector springs can be eased off. The gears will not slip out unless worn. The gearbox should be filled halfway up the shafts with gear oil.

Brakes. – The brakes of later cars are similar to the design used for years on the G.P. models, but are smaller and, of course, are not, as powerful as more modern systems.

Rear Axle. – Ratios: 13 x 45 and 12 x 45. Felt oil retaining washers are fitted at differential end of axle shafts. If oil leaks on to brakes, 1/4″ drain holes can be drilled in the rear axle casing, at the brake drum end, just before bottom dead centre.

On 2-seater cars it is usual to lower the rear of the chassis by altering the rear spring. The camber can be removed by a spring smith or leaves removed or wedges inserted.

General. – The Bugatti shock absorbers consist in effect of internal expanding shoes. These can be relined with Ferodo. It set tight they are apt to seize up, so are best assembled with a dressing of castor oil. Tight settings are not necessary as the road-holding on good roads is first class and on bad ones such settings knock hell out of the car. On the whole, a set of Hartfords are desirable, as being easier to adjust.

Incidentally, the Bugatti “shockers” can be adjusted (if the linings are sound) by packing behind with strips of emery cloth, setting the gaps of the shoes equally.

The steering never gives any trouble and is proverbial. The road wheels should be balanced and the “toe in” checked and, if necessary, adjusted by washers behind the inner cup of the ball joint. Stub axle pins are fitted with a curious lubricating system and are consequently neglected.

Replacement pins can be made locally. The old bushes are trued up and a new diameter pin made to fit, ordinary grease gun lubricator fitted to both bushes and the pulley attachment for the brake cable fixed to the new pins.

To conclude, a few notes on driving will not be out of place as they bear a good deal on the life of the car.

The chief point is that owing to high gear ratios it is possible to do as much harm at low engine speeds with wide throttle openings as by over-revving. The gears must be used. Second gear in towns and for pick-up, third gear for accelerating to higher speeds and top gear for cruising. It is possible with correct carburation and ignition settings to come down to about 1,000 r.p.m. on top gear with light throttle opening and to pick up by delicate movement of the accelerator on easy going only, but flexibility on top gear in the present-day sense is not possible. In gear changing a good clutch is important and the slip-through principle is best because of the close ratios, and is easier at higher road speeds because one is apt to over-rev, at low speeds when changing down and be too slow when changing up.

Lastly, observe the maker’s engine speed limit (3,800 r.p.m.) and never “step on it” until the oil is thoroughly warm.