1923 3-litre Bentley overhaul

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Sir,

The following is an account of the overhaul of a 1923 3-litre Bentley short-chassis model, known as the “TT” type. The writer has long desired to own a short-chassis vintage car of this make, and having been lately released from service with the Army after four years in various parts of the world, he decided that now was the time to buy the car and carry out a fairly comprehensive overhaul of it. The writer is an amateur, in that he is not connected in any way with the motor trade, but he claims a fairly wide experience of the older type of vintage sports car, having owned and overhauled two “12/50” Alvis cars and a Sports Riley Nine, amongst dealings with 2-litre and 11/2-litre Bugattis.

The equipment available was a good quality 9-in swing lathe, a small bench drilling machine, and a bench grinder, with the usual complement of hand tools and unlimited ingenuity. The car was purchased in February of this year, and delivery by rail was surprisingly quickly effected. Some little excitement was experienced in removing the car from the railway goods station to the writer’s home, a distance of about a mile and a half. The engine would not start (it had been standing for nearly the whole of the war period) in spite of liberal (perhaps because of) priming of the cylinders through the cocks provided for the purpose. We managed at length to prevail upon the good offices of a gentleman with a Buick who, with a short steel rope and some very willing horses under its bonnet, not to mention a slipping clutch, gave its the necessary assistance to a point about 400 yards from our destination at the foot of a fairly steep but short hill. Here the Buick’s clutch protested more than ever, and we thanked our benefactor and let him depart. There was then nothing for it but to make the Bentley engine perform. As we were then at the top of another hill much less steep but about 300 yards long, we decided on a do-or-die effort, and put the car into second gear. The clutch was let in after about 100 yards and the magnetos switched on. With much hesitation the engine fired, and with a lot of careful throttle footwork, we managed to coax the car the remainder of the distance.

Before beginning the overhaul the engine was run for a while and notes taken for later guidance. The machinery did not sound so good ; the big-ends being diagnosed as very slack, while the musical sounds from the pistons suggested either very much worn bores or worn gudgeon pins. The valve gear was very noisy, not that one expects a 3-litre to have Rolls-Royce sound-effects when running.

Eventually the overhaul was started. It was noted with satisfaction that there were no water leaks and that the upper half of the engine at least was externally quite clean. The less said of the lower half the better, as it was obvious that for many miles of travel more oil had been lost by leakage than by being burnt. One thing which immediately impressed the writer was the ease with which the bits and pieces were dismantled. The nuts came off their studs and bolts as though they had been fitted and not forced on to their respective threads as would appear to be the case with some of the more modern cars to which the writer has had occasion to minister. Most of the parts were numbered. Acts of contortion were not necessary to get at the important parts, nor did one feel the need for rubber screwdrivers or universally jointed elbows or five pairs of hands. The layout is so straightforward that there was never any doubt as to the correct sequence for dismantling or for reassembly.

Surprisingly, the car was in fairly decent condition, with nothing which could not be made as serviceable as it was on the day on which it was turned out by Bentley Motors Ltd. After 21 years of life this was rather remarkable. The car had been rebored during this period, and the wear since this rebore was at maximum just .010 in. The worst feature of the engine was the wear in the little-end bushes, which were very bad. The lower half of the engine was in a filthy condition, sludge being present in very large quantities. The main bearings were poorish, as were the big-ends, and it was decided to have all these replaced and the crankshaft ground.

The cylinders were duly cleaned up by removing all the aluminium alloy fittings and steeping the block overnight in very strong solution of caustic soda. This method produces very clean combustion chambers and ports, and the writer is surprised to hear that more people do not thus avoid the chip and scrape performance. The caustic does not affect the bronze water jacket covers nor the “Hallite” packings, as these were left in position and the block has been pressure tested since and found to be OK. As the pistons for the rebored cylinders could not be delivered for three months, the remainder of the engine and the rest of the car formed the subject of a leisurely and thorough overhaul. The camshaft and rocker gear was next inspected and was found to be fairly good. A thorough clean-up of the rockers produced very nearly unworn cam follower pads, though the rocker-adjusting screws and the valve stem tips were not so good. These were ground up in the lathe and rehardened by the “Kasenit” process and the valves, which were in some cases bent, were straightened and the faces ground to the correct angle. The bevels on the upper half of the vertical drive had at some time been badly assembled and were rather worn. It was decided however, that these were not sufficiently far gone to replace if a little noise could be tolerated and they were eventually reassembled and adjusted as near as was possible to correct mesh. A new thrust washer was fitted beneath the top bevel. The reground crankshaft was then fitted with the new big-ends and mains and a new double-thrust ballrace was fitted to the nose of the crankshaft. New valve guides were made by the writer to an exact copy of those fitted on dismantling, and it was noticeable that the valves required very little grinding in to ensure a good seal. One point of interest was that when time valves, rockers and camshaft were assembled and the clearances correctly adjusted, the rocker-adjusting screws bore rather on the outside edge of the valve stem. As there was no method of adjusting this it was concluded that it is a feature of the design. One very tedious job was the refitting of the camshaft bronze bearings. There are five of these and they were all slightly worn, and the writer’s object was to bed the camshaft in to a better fit than it had been before. In this he succeeded, but a very large amount of labour was expended for what will probably be of doubtful benefit.

It must be borne in mind that the car is very nearly in the state in which it was first listed by Bentley Motors Ltd. It is one of those 3-litres which (to the writer’s way of thinking) over-enthusiastic people have not fitted with cycle-type wings and comic running boards, and it has been the object to restore the engine and the car generally to its original condition. The remainder of the car has been wonderfully improved (though it could by no stretch of imagination be said to be in bad condition) by the expenditure of time and trouble in finding bits and pieces with which to do up the upholstery and deal with the cracks (only one of any importance) in the aluminium of the bodywork. The one bad break in the body was at the bottom of the right-hand windscreen pillar. This was covered up and strengthened by rivetting in place a piece of heavy gauge aluminium, which forms an arm-rest fitting closely over the cutaway portion of the driver’s side of the body. This patch has been carefully shaped and polished, and it now looks as though it as originally intended to be in that position.

Generally speaking, the transmission was in excellent condition. The gearbox was clean and the teeth unmarked. The rear pot-type universal joint required replacements in the shape of a set of blocks and slippers, which were obtained, after much searching, from Central Garage, Bradford. The car is fitted with front-wheel brakes, and when it was bought the writer was informed that the brakes had been attended to recently, and this was found to be true, as the drums and linings were in perfect comlition.

An opportunity is now awaited with growing impatience, to see how the car will perform on the road, but. it is feared that this will be difficult of accomplishment until the end of “the trouble.”

The writer is anxious that the very willing answers to queries which he has made to Bentley Motors Ltd, and others whom he has badgered with questions, including Tom Mitchell, of Blackburn, and Mr Henry, of Grosvenor Garages, Manchester, shall be placed on record. Indeed, he is grateful for the thrill of seeing envelopes in his morning mail with “Rolls-Royce” printed on the war-time economy labels.

I am yours, etc

J Yates, Blackburn