MY BIRKIN BENTLEYS
tla the following article Peter Robertson-Roger gives Some hitherto unpublished information about his two super
charged, 41-litre Bentleys. They were No. 1 and 4 of the late Sir Henry Birkin’s famous team, which was financed by the Hon. Dorothy Paget, and rated during the 1929-31 seasons. No. 1 is the singleseater which held the Brooklands Lap Record ; No. -1 is the short-chassis fourseater which finished second in the 1930 Pau G.P. When we tested the latter in 1937 it lapped at 102.69 m.p.h., and went from rest to 50 m.p.h. in 8.8 seconds and from 10-80 m.p.h. in 20 seconds. Now Louis Giron has put in the engine from No. 1 it should be much quicker, and has already done a fast run to Oxford in his hands. 1,Ve must match it against Lycett’s 8-litre when real petrol is again available. These special Blower Bentleys must not be confused with the production, blower 41-litres. Only two others were built ; one belongs to Mavrogardato, the other is believed to be in Prance. Robertson-Roger has kinclly written this article for us, and it says much for his keenness that it was done in bed, as his leg is not yet mended.—Ed.j. IN agreeing to write this article on my Birkin Bentleys, I naturally thought I had an easy task. After all, I ought to know something of the matter. Three obvious headings occurred to me : ” Historical,” ” Technical,” and ” Per sonal.” A little thought showed they were not so good. Historically, most
readers of MoTOR SroRT would be just as well informed as I—indeed Birkin’s performances with the single-seater must still be fresh in the minds of most of us— technically I should fail to grip, for my knowledge is not great, while anything coming under ” Personal ” would be construed as dull, bigoted or merely a fanfare of Roger trumpets.
But I have a great love for my Bentleys, which have given me endless pleasure. Both were purchased with the main object of preserving them—the four-seater to save it from passing, via a rapacious dealer, into the hands of an unappreciative owner with a penchant for showing off—and the single-seater because it seemed high time someone rescued it from an ignominious and half forgotten retirement.
The fervent competition enthusiasts, changing their cars at least once a year so as always to have ” the latest,” to whom the contest is the thing and the car just an instrument for it, will probably smile at this ; but it is just a matter of the point of view and they can always skip the rest of the article. I have always had a predilection for the big car, so admirably exemplified by the Bentley, and I have not yet seen the car I would rather own, either as a possession or for the pleasure in driving it. This probably sounds disgustingly self-satisfied, but there it is. As remarked above, the history of the Birkin-Paget team is well known, but perhaps a few notes on the cars under review w? add be of interest. The singleseater is No. 1 and the road car No. 4, and most of the engine components are stamped with these numbers. Incidentally, No. 2 is the other short chassis car, belonging to Mavrogardato, while Paul Marx has No. 3, the long, or rather normal chassis machine. After much studying of photographs, it was decided that M.avrogardato’s car was the one driven liv Birkin at Le Mans in 11130 while he drove mine at Pluenix Park, Ulster T.T. and in the Pau Grand Prix. He finished fourth at. Phetnix Park after breaking an oil pipe in the final stages and crashed
at Ballystockart in the T.T. At Pau, he finished second, after what must have been one of the greatest drives in history, against the cream of Continental drivers on out and out racing cars. Considering their natural superiority in braking and cornering, the Bentley’s speed on the straights must have been tremendous. Among the spares I have is a straight through exhaust system covered with mud, on which is a small aluminium plaque with the words ” Pau 1930. Removed from No. 4 car.” The Brooklands races of the singleseater are too numerous to mention here in detail, but one stands out above all others—the match race against John Cobb and his Delage, which the Bentley won by a couple of lengths, putting in a final lap at 137.3. It is said that altogether the single-seater covered over 50 laps at 135 m.p.h. Or more during its
career, There are many who have criticised the car on the score of steadiness, but it is significant that Birkin never mentions it in his book, and from the many alterations in shock absorbers, weight distribution, etc. it is obvious that much thought has been expended on the problem. Of the immediate history of the cars when the team was disbanded, I am, of course, unaware. It would be of great interest if anyone who owned any of the cars immediately after their racing careers were to write in and give his impressions. My car I did not purchase until 1935, when it was owned by Mr. R. C. Murton-Neale, who had run it in an Outer Circuit race and succeeded in finishing second, with a lap at 127
He told me that the car had belonged for a while to Chassagne, who prepared it for the Belgian 24 Hour Race in 1931 or 32, but it was not ready and never ran. One of the cars, No. 3 went to France for a while, and was twice entered for Le Mans by Trevoux.
believe it crashed each time. A few months after taking delivery, a piston broke during a run to Scotland
in the summer. Incidentally, this occurred at Penrith, which we had readied in a little over five hours from London. Lest anyone should imagine this is another average speed story, I hasten to point out that we left London at 5 o’clock in the morning ;* but it did give me an idea of the very high average the car could put up, especially as we had made no attempt to hurry, since we had all day in which to complete the journey. Anyway, the car was repaired at a small but efficient garage in Dumfries, but through a natural ignorance, the standard Bentley pistons were fitted, very long ones with a ring at the bottom, which absorbed much of the engine power. The result, of course, was a considerable reduction in performance, though reliability, in the shape of almost complete freedom from plug trouble, was
improved. Later, a new type of very light piston was tried, resulting in a slight improvement in acceleration, though the maximum remained at about 112 m.p.h., the last 1,000 revs, in any gear being somehow hard to come by.
However, in its detuned state it made a very reliable and pleasant road car, and really possessed considerable speed. On the way up to Shelsley one time, I recollect being passed with a rush by Earl Howe on an Alfa-Romeo. Thinking it it would be amusing to hitch my wagon to a star, I gave chase and the Bentley held the speed of his car quite easily. Perhaps he was merely loitering. In such competitions as were entered, nothing was done to the car by way of tuning ; its only successes were at a Vintage meeting near Hartley Whitney when it won two Classes and was second
in another. Lewes was tried without success, and also in 1936 the car finished fifth in the Bentley Drivers’ Club Race at the October Brooklands meeting, the flying lap being 103 m.p.h. Then at the beginning of last year, I heard of a more or less standard blower Bentley which had been prepared for an Outer Circuit race at Brooklands, had lapped at 123 in practice, with full equipment and been rejected by the stewards as tub fast for the entrant, who was new to Brooklands racing. I discovered it had been prepared by Louis Giron at Hampton Court, and to him I forthwith repaired, to see what could. be done about mine. He quickly discovered that a rebore and new valve guides would be necessary, and that the compression ratio was actually lower than standard I Thus the missing 1,000 revs, were ex
plained. New Martlett pistons were fitted, bringing the compression up to 6.5 to 1, and the original S.U. carburetters, which were showing some signs of wear, replaced by two Zenith Triple Diffusers, most remarkable instruments which seem to give an amazing urge high up in the speed range. The brakes came in for a lot of attention and were very greatly improved. Several detail modifications were carried out, including the fitting of a beautiful little air pump driven by a propeller, to maintain pressure in the fuel tank on long runs—and a great joy it has proved. Eventually the car was completed and run in, and it was evident that a great improvement had been effected. During carburetter tests at Brooklands, it went up to 120 m.p.h. with consummate ease on fairly soft plugs, Champion R.1 on the exhaust side and R.3 On the inlet. The urge at high speed was fascinating ; 100 m.p.h. for instance could be held
‘comfortably on half throttle, and even from that speed, the oomph which. was forthcoming was quite astonishing. This success encouraged me to enter for the United Hospitals and Vintage
meeting at Donington last May. It -was decided to see what the performance .would be on ” dope,” and accordingly only racing classes were entered, though the -car ran fully equipped. The increase in performance was most marked; in practice the Bentley reached 115 on the uphill stretch and over 120 the other way. The brakes too, came fully up to -expectation, slowing the car in magnificent fashion on the awkward hill down to Melbourne Corner. But in the actual race came disaster leaving the top corner I held on to bottom gear a fraction too long, there was an appalling -crash from the emgine and a great cloud -of smoke blew back into the car. A connecting rod had snapped at the bottom, smashing through an engine bearer on one side and the very non-standard sump on. the other. Things looked bad. There was no use blinking the fact, the engine would have to be entirely rebuilt, and the only way -of doing this really well seemed to be to ‘purchase the spares, and perhaps the single-seater, which was in almost for gotten retirement at Welwyn. So at last, after much charging up avenues and overturning stones, I set forth in a large lorry armed with a permit to remove the single-seater and all the spares I could find. The business of removing the car would almost form the subject for an article by itself, not the least of our troubles being the extraordinary difficult) of inserting my admittedly fairly
ample form into the driving seat. Indeed, when we stopped for lunch, it was almost decided that it would be quicker to bring out something on a tray; kind friends who were supposed to be assisting in the removal spent most of their time alternately laughing or taking photographs Of my embarrassment. Back in the workshop, it was decided that the best plan would be to transfer the engine of the Single-seater more or less entirely, vandalism though this seemed at first. It has the much discussed big port block—probably the only one in existence—a much larger and superbly made crankshaft, the most beautiful set of steel connecting rods and a much lighter flywheel. The clutch, too, was transferred. The main bearings, though perfect, were re-metalled with more modern material, and the Water system altered to get an improved flow past the exhaust Valve seats, which used
to be liable to crack. The lubrication system needed alteration, as the syStem on the single-seater differs considerably. A brand new supercharger from the stock of spares was used, and various other detail improvements and innovations effected.
The car has only just been completed and I have not yet driven it. I am told that the improvement is wonderful, the big crankshaft giving a truly remarkable degree of smoothness. The performance, too, should be considerably -enhanced. Finally, the single seater will be rebuilt and used on the road, in as near
original condition as possible. In this connection, the only parts needed are the upper half of the crankcase and a set of connecting rods ; if anybody knows where these articles may be obtained at a reasonable price, I should be eternally grateful for the information.
And now, in case you haven’t noticed it, there is a war on, the infernal flying machine needs the whole of the world’s petrol supply and there we are. Anyway, it’s all been great fun, and no doubt the Bentleys will sleep soundly under their coating of oil and their dustsheets, until the happier days come again.
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