"Babs" engine–was Parry Thomas careless?
SINCE Mr. Owen Wyn Owen of Capel Curig disinterred the 27-litre Thomas-Special “Babs” a number of mysteries about the car have been posed not all of them relating to how it killed its driver. For instance, last October a correspondent who had seen “Babs” in Mr. Owen’s garage reported that Parry Thomas was apparently unaware of the correct lubrication procedure for a Liberty engine or didn’t bother, because on the dismantled engine of “Babs” the upper bearings of the drive-shafts to the o.h. camshafts were found to he damaged and one had half melted away. This led to a reader. Mr. S. W. Layfield of Onchan, lending us a handbook for the Liberty aero-engine, from which it is clear that in these engines “the camshaft circuit is served. last by the feed pump and will therefore be the last to receive an adequate supply (of oil) when the circulation is sluggish” under such conditions it was stipulated that “one of the camshaft casing lids may be removed and hot oil poured in”. Also it was made plain that if the engine had been standing for a week or more besides doping the main thrust bearings (of the camshaft drive-shafts) the camshaft casings should he doped with half-a-pint of oil through the plug holes machined in each of the front covers and the upper drive-shaft should have been doped through the oiler at the base of the generator (these engines had coil ignition). Further, it was stated that before starting an engine which had been idle for some length of time it was advisable to inject a small quantity of lubricating oil, about half-an-ounce, through each priming cock. The engine should then have been turned over five or six times to distribute the oil.
Although both Clive Gallop for Count Zborowski, and Parry Thomas were capable engineers, it seems possible that in the car these precautions were neglected. Incidentally, these camshaft driveshafts had two ball-hearings at: their lower ends and phosphor-bronze bearings at the top, as our correspondent suggested. Another query that has been raised is how was “Babs” started, in the absence of carburetter chokes? Presumably the four Zeniths were enriched, maybe with rag, as the car was push-started. but the official method was to turn the engine while operating the priming pump, giving three pumpsful in normal temperatures, then turn the engine over twice, then turn it until the main contact-breakers were open. then switch on and press the starting-button buzzer. The engine was then run slowly for 30 to 45 seconds, or longer in cold weather: run on the second switch at a speed at which the ammeter read zero, and warmed up like this until the radiator thermometer read 65 ( and the oil-system was at 40″C. The ignition was then to he advanced and the engine accelerated to 1,400 r.p.m. for a short while, alter which it had to be accelerated and slowed once or twice to throw oil up into the cylinders. It was added that after three minutes’ running the oil pressure should rise to 5 lb per sq. in. and at 1,400 r.p.m. show a maximum of 25 to 30 lb.sq. in. (This was with the standard two HC7 carburetter between the vee of the cylinders, feeding through four aluminium manifolds, the forward carburetter feeding cylinders 6, 5, 4 port and starboard the rear one cylinders 3, 2, 1 on each side. Thomas had altered this using four Zeniths, two at the front and two at the back of the engine) I do not know whether Gallop and/or Thomas were conversant with this starting procedure with these stipulations but I hope to sec Wyn Owen observing some of them in the not too distant future, when he starts on the resuscitated “Babs”.
I do not know whether Gallop and Thomas observed this starting procedure, not easy in a car without a starter. Incidentally, the rev. limited quoted for a 1924 Liberty were 1,400 r.p.m. warming up. living at below 6,000 ft., 1,650 at or/ above this speed and 1,750 . the maximum. This American 45-deg. 2.4-valve 127 177.8-mm V12 engine with its welded water jackets normally had a cr of 5.31 to 1 4.78-tot pistons were not usually issued to the RAF and it gave 405 b.h.p. at the the normal speed of 1,750 r.p.m., 425 b.h.p., (Thomas claimed to have increased the output ; some authorities quote 500 to 600 b.h.p. at 2,000 r.p.m.). The dry weight was 820 lb.m the gross weight 1.083 lb., and the valve timing was opens to deg. a.t.d.c., closes 45 deg. a.b.d.c., exhaust opens 48 deg closes 8 deg. a.t.d.c. Maximum ignition advance was 30 deg.
It will be interesting to learn how much Thomas departed from the timings, etc. . . with his special camshafts, pistons and manifolding, etc. Wilde on the subject of “Babs”, the recent epidemic of Asian influenza makes one sympathise with Thomas, who set out for Pendine and his last drive only partially recovered from ‘flu, 1927 version. I understand he felt so weak that be contemplated stopping between Brooklands and Pendine but felt better after dinner in Oxford and pressed on that evening to his destination. I have heard he was driving a 3-litre Invicta.-W.B.