About the Bentley 4.5 Liter Blower

Walter Owen Bentley, better known as W.O., started to design and manufacture his famous sports cars after studying steam engines for a period of five years. So, in 1904, when he was sixteen years old, he began his training as a steam locomotive engineer. It was the fact of the steam engine being the machine which best demonstrated the balance between form, strength and speed which led to W.O.’s fascination with them. But perhaps the thing which excited him most was the speed, and so he dedicated his free time to competing in car races. He competed against Rex and Indian, and his sporting experiences include twice entering the Isle of Man Tourist Trophy, which comprised of pure speed tests, hill climbs, and velodrome races—including some at Brooklands.

In 1910, the 22 year old engineer stopped working with locomotives and spent two years on the technical supervision of several hundred taxis, including their repair and maintenance, at the National Cab Company in London.

With the start of the first World War in 1914, Bentley founded the first British firm to make aviation engines which used aluminum pistons: the air-cooled Bentley BR1 and BR2, which had star cylinders. This resulted in them being among the best and most powerful in the allied forces. In 1919, Bentley founded his own car company with the aim of manufacturing, “a fast car, a good car, the best of its kind.”

The first car with a three litre engine was completed in 1919, and a month later he sent that car to the Olympia Motor Show. Orders started coming in, and a few months after that, he carried out his first road test; news of which was published by The Autocar. After this even more orders came in, and a small factory was founded in Oxgate Lane, Cricklewood. 

The first 3 litre Bentley, a coupe, was launched in September 1921. This model was manufactured until 1923, and, despite its high price, 1,619 cars were sold. Its basic characteristics, however, were maintained in all the Bentleys made at the Cricklewood factory, where they made cars with 3, 4.5, 6.5, and 8 litre engines.

From 1931, the only part of the original car remaining was the name and the Bentley grill. This meant it had a very short existence—twelve years full of expectation, glory and fame—and also constant financial problems.

When the organizers of the car marathon at the La Sarthe circuit invited W.O. Bentley to participate, he declined. Bentley claimed that his pure-blooded cars weren’t built to race for an entire day and night. Later, when he realized that there would be nobody flying the flag for Britain, he reconsidered and decided to race.

The race, with W.O. in charge of the team, didn’t turn out very well. The driver and official test driver, Duff and Clement, managed to hold onto the lead for a while. However, halfway through the race, a stone punctured the fuel tank. Duff ran 5 kilometers to get to the boxes, and Clement, on a borrowed bicycle and with 2 cans of fuel loaded onto his shoulders, made it to where the car had stopped. They managed to restart it. Despite these huge efforts, their rivals had gained a large advantage, and the Bentley had to settle for fourth place. The next year, in 1924, luck was with them a little more than the previous year, and the Duff-Clement combination made its mark on Le Mans. They covered over 150km more than the second placed team.

W.O. Bentley had already changed his opinion about the 24 Hours, and in 1925 he entered two cars: the usual Duff-Clement team, and a new team of Bertie Moir and David Benjafield. Racing with the convertible top up, Moir-Benjafield’s car consumed a lot more fuel than they had anticipated. The car stopped twenty kilometers from the official refuelling point. The other car practically took off and finished in second place.

Three Bentleys lined up for the 1926 race, including a new model—the Super Sport—which was lighter and faster. Twenty four hours of misfortune ensued: two cars ended up in two separate accidents, and the third retired twenty minutes from the end. The following year, W.O. Bentley added a very fast 4.5 litre car with the other two 3 litre cars. All the vehicles were equipped with a device which allowed the driver to regulate the brakes, as the brake shoes wore out. 

The famous race driver Sir Henry Birkin, together with Clive Gallop and the expert in supercharged compressors, Amherst Villiers, developed a supercharged version of the 4.5 litre Bentley. It was much faster than the conventional 6.5 litre cars. This decision was made against W.O. Bentley’s will. He was somewhat wary and didn’t really trust the engines, although while they lasted, their speed was incomparable. Proof of this is Birkin’s still standing record at the former Le Mans circuit. 

Regulation: front longitudinal

Type: four linear cylinders, water cooled

Cubic Capacity: 4.398 cc

Diameter x Stroke: 100 mm x 140 mm

Compression ratio: 5:1

Distribution: four sloping valves per cylinder controlled by one overhead camshaft on a vertical axle from the crankshaft.

Regulation: gearbox following the engine. Rear-wheel drive

Clutch: dry, one disc

Gearbox: 4-speed with manual change. 1st -2.66:1, 2nd -1.65:1, 3rd -1.35:1, 4th -1.00:1

I started making this model with the challenge of improving on my previous model, the Bugatti Type 59. In reality, the Bentley is a very demanding car for a model maker, due to the fact that many of the mechanisms are on display—so they have to be perfect. Once again, I decided to work to a scale of 1/10, as this size allows maximum detail and enables me to make all the mechanical parts, including authentic screws myself.

From the outset, I had to assemble good graphical documentation based on various articles from different magazines and specialist books about the Bentley. I realized straight away that, despite having all this information, there still wasn’t enough to enable me to achieve the quality of workmanship that I desired. Therefore, I carried on investigating until I found a Bentley 4.5 litre in the Antic Car Club de Catalunya, whose President was the owner of the car. It wasn’t the supercharged version, but it served 80% of my needs. 

The wheels on the Bentley are Rudge Whitworth type, spoked with 6×15” Dunlop tyres. Making the wheels always requires special care, as they are a very visible part of the car which attracts your attention. The eighty spokes are mounted on two levels, and have to be exactly to scale, although this includes laminating the rod to make the spoke to scale. Each one has to be precise, as differences in thickness would make it inaccurate.

I started the process by planning all the steps for the framework of the spokes on paper. Then, I put a round piece of brass in the lathe to begin to reshape the rim. I repeated the same operation to make the different layers of the axle casing/housing. I used brass for these pieces, as they would later be painted in British Racing Green, like on the original model. In addition, I had to draw all the holes on the rims and axle holes on templates on adhesive paper. In total I drilled 800 0.5 mm holes, and this required extra special care. I had to make a small bradawl master to make the small bulges in the rim where the spokes separate.

Like in the previous model, the chassis is made up of two longitudinal tie-beams, and three main crossbeams, which were then used to support the compressor, the engine, and the gearbox, as well as supporting other mechanisms.

The first difficulty I ran into was doing the scale drawing of the original model, given that it is a very long piece which has numerous curves. These all have to be perfect to achieve the desired effect, as this forms the skeleton of the car.

I used a brass handrail, and then I drew the profile of the chassis on the widest part, and the curves on the upper part of the handrail. After that, I fixed this piece with clamps to mill the curves of the tie-beams. Once this operation had been finished, I changed the position of the fixings to enable me to mill the definitive profile of the tie-beams. Then, when the upper part had been hollowed out, I was able to solder the crossbeams and the tips with silver. That completed what would be the backbone of the model.

Aluminum is not as easy to machine and additionally, drilling and threading is much more difficult and risky with aluminum than brass. Another disadvantage is that it is impossible to solder pieces of such small dimensions.

This model incorporates a wide range of screws, measuring 0.7, 0.8, 1.0, 1.2, and 1.4 mm. Moreover, hexagonal screws made by myself have also been used. This required great effort, but it was worth it in order to achieve the perfection that I was looking for. We’ll now move onto how I made all the previously mentioned pieces which were then incorporated into the chassis. 

The compressor is one of the brightest and most colourful parts of the car. It is an Amherst Villiers Roots, and attracts your attention due to it’s size at the back of the chassis. The head of the compressor required complicated milling due to the different circular parts that make it up. I also had to drill various holes to be able to hold the piece using 1 metric screws. 

Following that, I made the body or central part, laterally milling it with an ‘H’ shaped tool to make the cooling fins. But also remembering to leave spaces in between for the pins which would hold the compressor head. The final part was a round piece which I made using a simple turning operation. After that, I made the finned outlet pipe that is fixed onto the left hand side of the compressor. 

The radiator grill on the Bentley has a single form, specific to this make of car. I started to mill it from a piece of brass, taking into account that it would have to be finished by hand on a lime base, given that it doesn’t have consistently smooth curves. The upper part of the block is maximized to work on the body of the radiator.

The front grill is made of stainless steel, and it is important that it is to scale; the light spacing as much as the diameter of the grill. The top/lid is the most complicated part of the grill due to its reduced dimensions. I made it like the real one, so it could be opened and closed. The most challenging part was getting the pressure right for the closing mechanism.

The small top is made up of no less than seventeen pieces of brass, which were then nickel-plated. They all have to move perfectly, and one of the most difficult parts was making the two wooden handles on the upper piece.

The gear box is separate from the engine, and is situated in the middle part of the chassis. There is a short transmission driveshaft from the engine to the gearbox back, and a second drive shaft with universal joints at each end from the rear of the gear box to the differential at the back axle. It is made almost entirely from aluminum—the only parts made from brass are the register heads. On the right hand side of the gear box you can see the transmission arm where the gear-change is situated.

From the back you can really get a good view of it, and appreciate the size of the petrol tank. I used 0.8 mm brass sheet to make it, made into a strip and then formed, as on the real car. The mesh protection is in place because at that time the roads were generally gravel, and it was quite normal for stones to fly up off the road and puncture the petrol tanks.

In the upper part is the petrol filler and the petrol cap, which have the same pieces as the radiator but on a larger scale. The petrol pipes are located on either side of the tank, and have four taps to open and close the petrol flow.

Due to the length of the bonnet and the fact that the engine has four cylinders, the firewall protrudes slightly compared to the bodywork, which adds to the car’s attractiveness. This means that it was necessary to detail the firewall on both sides. This protrusion of the firewall leaves the back of the dashboard exposed, meaning it was also necessary to detail it with precision, including the cables. The complexity of the firewall and dashboard meant that I spent more than six hundred hours on them.

Basically, it is made up of a mixture of 1, 3 and 6 mm brass sheets where I positioned the dynamo with its connection to the engine, the current regulator, two petrol tanks, angular supports for the dashboard, the accelerator, two connection boxes, and infinite connection pieces which go from one side of the firewall to the other—carrying pipes with oil, water and air.

Like in the real model, I used aluminum to make the majority of the engine. As I said earlier, working with aluminum carries a great risk, due to the fact that it is much more durable than brass, and very common for drill bits and pins to break whilst drilling or threading.

The engine is made up of three main parts: the block, the cylinder, and the cylinder head or rocker lid. It is supported in the chassis by three points: at the front; the part where it connects with the compressor; and the two arms which separate the block, and rest on the tie-beams of the chassis.

The detail on the engine is a different matter altogether. You have to begin by making the largest pieces first, moving down to the smallest pieces last. Firstly, I milled the drive shaft and the arm which supports the two magnetos. the bodies of the magnetos were made from ebonite like on the real car, and the magneto insulation is made of bakelite.

To make the bodywork, I fabricated a master copy from wood, which served to mould the brass sheet I used in the bodywork. I shaped the brass sheet using a hammer, and then assembled the additional parts with soft solder. The interior panels and the seats were made of wood, and then covered with leather. When the interior panels fitted well, I cut the doors out and made the hinges and locks.

If we want to see a complex dashboard, then the Bentley is a perfect example. It has no fewer than nine clocks, five switches, and three other controls. To begin, I drew the plan of the layout of the clocks and controls. 

Next, before separating it from the plug and using the wooden turning machine, I made the 969 circular marks. I kept the same order and sequence as on the original car, only ten times smaller. Next, I moved on to the lathe to make the bases of the clocks and the faces.

The steering wheel was made from brass, which I painted black. I then wound string around the hoop to give it the same effect as the original. The windscreen and the protective grill were also made of brass, and then nickel-plated. The system of bars on the roof will be the last parts to complete the model.