The Bentley Brains Trust

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It was a happy thought on the part of Stanley Sedgwick, Secretary of the Bentley Drivers’ Club, to form a “brains trust” of real Bentley celebrities, so that members might glean first-hand information relating to their cars. Under Question-Master Kenneth Horne he assembled W. O. Bentley himself, W/Cdr. Woolf Barnato, H. Kensington Moir, Lt. Col. Clive Gallop, L. C. McKenzie, and “Nobbie” Clark.   F. C. Clement and S. C. H.. Davis were unable to attend. We expected a very serious and technical session but such was hardly the case. Kenneth Horne led things along in the best “Light Programme” manner, and Kensington Moir proved himself every bit Horne’s equal as a comedian. The result was a hilarious evening which gave the impression that vintage  Bentley owners of the  present day prefer the noggin to the natter. This was all the more surprising in view of the presence of the “patron of the marque” and the general “quality of the brains”; it is a sad fact that technical replies called forth interruptions from certain sections of the audience. This was no fault of the “brains,” who did their best to meet the prevailing demand. As a jolly, rather pointless party the thing was great fun, but there was little opportunity of advancing one’s technical knowledge of a famous make.

Putting aside such matters as food and drink, female psychology, the New Look, the value of chewing gum as an aid to peace of mind and the making of passes at girls who wear glasses, the following summarises the findings of the “brains”  in respect of Bentley technicalities:

A query regarding the,standard versus the “Prestwich” Speed six cylinder block resulted in Clark and “W.O” denying all knowledge of the latter,  Clark admitting only to a two-port and single-port block, although McKenzie said it was accepted years ago that Prestwich had something to do with the design of the single-port head in conjunction with “W.O.”

Clark, answering a question about the whine of the Villiers blower being heard only at certain speeds, said a secondary torsion happened at 2,200 r.p.m., and a primary one at. 3,100, and the noise is heard at those r.p.m., due, he thought, to that torsion and noise resonance. The reason why No. 1 engine went into No. 5 chassis seemed to be due, not to a very wild night., as Kensington Moir suggested, but to engines 1 to 4 being purely experimental units, the fifth or first production engine being stamped  No 1.  Clark believes he knows where the first No. 1 engine is today.

On the subject of how the “works” cars differed from the production jobs, Clark, Moir, Barnato and “W.O” all stated that. apart from axle-ratio, compression-ratio, careful  assembly  and larger tanks, and special pistons on the 4-1/2-litre cars, the Le Mans” Bentley  did not differ from the catalogue cars. 

Lt.-Col. Gallop gave some very interesting data as to how the Birkin  “blower 4-1/2” cars were developed, which boiled down to a special slightly-stiffer chassis frame which he persuaded Meakins of Glasgow to make, assembled with fitted nuts and bolts made at Welwyn on a No, 2 Herbert capstan, no rivets being used. Special crankshaft, con-rods and pistons were designed by Amherst Villiers, the crankshaft having main journals of 80 mm. dia., and at first being a nightmare to lubricate. K.E. 965 exhaust valves never gave any trouble and were not sodium-cooled. The first Villiers superchargers had a double casing and time was lost in getting the complicated castings made. The indicated rotor clearance and rotor/casing clearance was one thou., but due to the inner casing overheating, and the outer casing restricting expansion along the length of the supercharger, the rotors used to touch the casing. It was found possible to retrieve damaged rotors by machining the tops clear of pick-up, and forming a labyrinth groove at the top of each rotor. Such rotors were eventually found to give a boost of up to 9-1/2 lb./sq. in. with a 4-thou. clearance. The blower gears were cut for them by Mr. Hukins of E.N.V., and had a 2-1/2 thou. clearance, and no trace was ever seen of the rotors touching each other. The early con -rods were too heavy and also too weak, and broke. Ultimately a rod almost like the standard 4-1/2-litre Bentley rod was used, but thicker in the web and sides. The single-seater  blower 4-1/2″  did over 4,000 r.p.m. (on a 2.73 to 1 top gear  —  Ed.), and Tim got over 4,000 r.p.m. on the road (on a 3.3 to 1 top gear  —  Ed.) at Le Mans. But putting up the weight caused a certain amount of trouble and when driven very fast  —  Gallop said, “with the greatest respect to Dunlop, and not in the least meaning any criticism of them at all ”  —   those cars were just too much for their rear tyres, although Birkin was second with a stripped version in the French G. P. at Pau. On which discourse the Question-Master commented that it was quite clear that the Birkin car was the model from which the 1935 Trojan was developed.

McKenzie remarked, in answer to another query, that the slightly heavier side-members of the 1928 3-litre noticeably improved steering. On the subject of modern-type filters, McKenzie advocated a by-pass type connected to the main junction near the filter, where the pipe to the o.h. gear comes away. Gallop preferred total flow filtering. Moir recalled that the original Bentley tail-pipe diameter was 2 in. of about 16 gauge, but the number of summonses resulted in a reduction to 1-5/8 in.

The session concluded with outstanding memories of the “brains” in connection with Bentleys.

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