I was interested to read Hugh Conway’s letter in the February issue on Bugatti breathers. I recall in the late 1920-30 period having a long discussion with the legendary Papworth on this subject. At that time it was clear that not all Bugattis suffered from loss of oil via the crankcase breathers.
The Type 37 Bugatti did have room for an oil filler which acted as a breather, plus the normal breathers on the crankcase wall, fitted with “dunces hat” wire gauzes inside covered by the aluminium domed cap.
The Type 37A had only two breathers situated on the exhaust side, as the supercharger occupied all the space on the offside and there was no oil filler. Thus oil had to be pumped to the engine sump from the oil tank beneath the passenger seat. This tank was connected to the hand pump on the dashboard, and the pump handle was lovingly known as “the butchers knife”. The engine sump required 11/4 gallons of oil.
In the sump was a set of sheet metal baffles and steel-framed gauzes all secured by common screwed studs. Thus oil passing away from the mains and big ends would have to negotiate the crankcase gauze in order to arrive in the sump.
My conclusions are that the engine oil pressure can be suspect if it is unusually high. This means that the volume of oil pumped would be too great to negotiate the sump gauze, and would thus build up above it, causing the crankshaft to dip its webs and throw up the oil at the breathers on the external wall of the crankcase.
As a guide, a Type 37 with centrifugal oilways in the crankshaft webs would need to show more than 2 or 3 kg/cm at 3000rpm, and just to have the gauge needle off zero at tick over. The Type 37, with high pressure oil system and unloader built in the oil pump terminals, would shew a bit more at 3000rpm, possibly 3-4kg/cm2.
Another source of over-oiling is the cambox, which is supplied by a connection to the crankcase oil gallery, the oil terminal of which is metered, by drilling the correct size for the all supply required. At the cambox level the oil terminals can be drilled somewhat larger as the metering is done at the gallery end.
The method of testing is to run the engine at 800rpm and to watch the camshaft and fingers. Oil should ooze out of the fulcrum points and contours. Should too much oil escape at these places it finally arrives by drainage back to the crankcase to exacerbate the situation there.
I do not think this is an epidemic and should the odd case be cured as Hugh mentions, this may well be the better method. From my experience, the only time I lost breather caps and gauges was from minor crankcase explosions, caused by piston crowns melting. There must be quite a few of these beside the track at Brooklands.
It is nice to recall Charles Brackenbury winning the Gold Star three years in succession on the outer circuit with a T37 at about 115mph, on a 2-litre supercharged Grand Prix at over 120mph and again on a 2.3 Grand Prix at over 126mph.
If any of these three Bugattis lost oil from the breathers Charlie would not have finished the race.
J Lemon Burton, Hassocks, West Sussex