Thomas Special grand prix car, information requested

This is my first post on this forum and covers both my enthusiasms, historic motor racing and making 1/32nd scale slot car models of historic racing cars to go fast as they can under the rules applied to the event. After 40 years I am not sure which drives which, as they are now so inter-wined

For while I having been asking whether any of my slot racing friends knew the dimensions of the Thomas Special. Recently one of them said that Atlas F1 was the forum to try, so here goes.

Racing scale slot car models of historic racing cars tends to be split into periods for authenticity and one is pre-1939 grand prix cars, or, if the organisers have got tired of the big Auto Unions and Mercedes doing all the winning, pre-1934 grand prix cars. One of the basic rules is that track and wheelbase must be scale for which there is a good database of information, but there is no information about the Thomas. To build a model that will pass scrutineering requires documentary evidence.

One of the rules of thumb for selecting a prototype to model that will be quick is that it must be long, low and wide, with a wide body to accommodate a motor and a chassis. The Thomas Special fits the bill, which is why I am keen to build one.

I am aware that Parry Thomas built many racing cars and they could all be described as “specials”, but the one I am referring to is the straight 8 grand prix car that ran in the 1926 and 1927 British Grand Prix at Brooklands, with limited success There is picture of it on page 60 of April 2006 Motor Sport competing in the 1926 JCC 200 mile race and also pictures in Bill Boddy’s Brookland’s history and William Court’s Power and Glory Vol1 page 152.

I would like to find out the front and rear track and wheelbase at least, but any other dimensions would be useful, especially overall wheel and tyre diameter as I have found a head on and a side on photograph which could be scaled if I had wheel sizes. The photos I have are black and white, one showing it a pale colour which probably is white as that is the colour Parry Thomas tended to paint his cars, but others are darker and could be green

Can anybody help?

Can I help? Er no.

But have you seen the book by Hugh Tours - Parry Thomas Designer Driver (pub: B.T. Batsford)? That might have the information. I know they've got a copy at MotorBooks in the West End. £45 I think.

Incidentally one of Thomas "Flat-Iron" Specials was hillclimbed post-war with a 4.5 litre Mercury engine. I don't suppose anybody knows what has happened to them since? Or the 1.8-litre Thomas Special?




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Welsh Motor Sport History

No dimensions immediately to hand Dick - but at least everybody here will now know what these wonderfully avant-garde little cars looked like.

DCN

Interesting.

From John Bolster's Specials:

All previous Parry Thomas cars were fitted with disc wheels, but in this case the new special was endowed with the fashionable Rudge wire type, presumably in the interest of rapid wheel-changing in the pits.

And yet the one in Doug's photo has disc wheels . . .

The one in Jenkinson's Racing Car Pocketbook, which is signwritten "THOMAS SPECIAL 2" does have wire wheels. No dimensions though

Originally posted by Tim Murray
Interesting.

From John Bolster's Specials:


And yet the one in Doug's photo has disc wheels . . .

Hasn't it just got aluminium covers fitted to the wheels?
They appear to be far too dented to be 'solid' disc wheels!

The wheel fixing would appear to be a center lock (Rudge Whitworth type) fitting as you would expect with wire wheels. And covers could have been fitted to aid streamlining.

In response to Dick's question about dimensions, he might be able to work it out from the wheel sizes?

I would expect the wheels to be 19" diameter - e.g. that would be roughly the diameter of the wheel discs.

The ratio between wheelbase & wheel size (assuming 19") would then give a wheelbase of 5'9", of course if the wheels were 20" that would make a 6 foot wheelbase.........

This is from the book Parry Thomas Designer Driver by Hugh Tours that was recommended by johnwilliamdavies.

The contemporary French magazine "Omnia" quoted
the wheelbase as 242 cm (probably a conversion of 95 inches),
the track as 127 cm (= 50 inches) (no differentiation between front and rear),
and the tires either as beaded edge 765 x 120 (= outer diameter x width in millimeters) or straight side 30 x 4.75 (= outer diameter x width in inches).

In my eyes, photo no. 23 of Catalina Park's post shows the car with the 765 x 120 tires.

the photo in the Jenkinson book is a 3/4 front view that was obviously taken at the same time as the two above. It doesn't convey any more information.

FWIW, it is credited to Topical Press Agency Ltd. but after 24 years I doubt if they still exist.

Originally posted by Dick Smith
This is my first post on this forum and covers both my enthusiasms, historic motor racing and making 1/32nd scale slot car models of historic racing cars to go fast as they can under the rules applied to the event. After 40 years I am not sure which drives which, as they are now so inter-wined

Dick, are not these guys fantastic? They simply amaze me!

Something new is learned each day.

Henry

I am fascinated to see pictures of the Thomas GP cars.

Whilst I appreciate that this thread concerns the dimensions of the cars, could someone supply details of the engines installed in them?

Thanks in advance

PdeRL

Originally posted by johnwilliamdavies

Incidentally one of Thomas "Flat-Iron" Specials was hillclimbed post-war with a 4.5 litre Mercury engine. I don't suppose anybody knows what has happened to them since? Or the 1.8-litre Thomas Special?

One of the Flat Irons is still in existence in the U.K. As far as I'm aware it is very much unrestored and I don't know if it still has its correct engine.

May I suggest you write to Bill Boddy and ask him to mention something in his column in Motor Sport? It might elicit a helpful response.
Indeed I recall an article on the car in question in Bill Boddy's page in a relatively recent issue.


JH

Apropos the colour: I have a nice French book called "La Vie des Pilotes de Course de 1919-39", which is illustrated with drawings and paintings by Michael Turner. The darker-coloured Thomas is shown in one of the paintings in what is best described as "Bentley green". It would be unlike Turner to get it wrong ....

Originally posted by VAR1016
... details of the engines...
PdeRL

1.5-liter straight eight composed of four aluminum pairs with steel liners,
bore/stroke = 52/88 mm,
detachable head made of cast iron,
single overhead camshaft driven by spur gears - two valves per cylinder - valves closed by small leaf springs,
crankshaft in five plain bearings - big ends in plain bearings - dry sump (oil tank serving as crossmember).
Trials with different carburetors and Roots blower(s) (water cooled).

Originally posted by robert dick

1.5-liter straight eight composed of four aluminum pairs with steel liners,
bore/stroke = 52/88 mm,
detachable head made of cast iron,
single overhead camshaft driven by spur gears - two valves per cylinder - valves closed by small leaf springs,
crankshaft in five plain bearings - big ends in plain bearings - dry sump (oil tank serving as crossmember).
Trials with different carburetors and Roots blower(s) (water cooled).

Wonderful, many thanks.

Presumably then, this engine was manufactured either by Parry Thomas (I believe he was a fine engineer) or to his specification. I do wonder how such a costly project might have been financed at that time - after all they were not "John Player Specials"!

Also interesting is the use of leaf-type valve springs. This idea was used on the Leyland Eight with which, of course, Thomas was very familiar.

Incidentally (and off-topic) leaf valve springs were also used on the Hotchkiss AR - whose camshaft resembled a little crankshaft!

Thanks again.


PdeRL

From Specials by John Bomster:
The engine was built by Peter Hooker, of Walthamstow. It was very unconventioal in design. The crankcase had eight holes along the sides, with quickly detachable covers.
All eight cylinder barrels were separate and spigoted into the crankcase. Light alloy water jackets were fitted, one to a pair of cylinders, four in all. A single, cast-iron deep section cylinder head was employed, and this sat on top of the eight cylinders and four water jackets, clamping the lot together. The head was pulled down on the crakcase by right-and left hand threated turnbuckles, through which holes were drilled to take a tommy-bar.
The cylinder head was a typical Tomas design, with the usual inclined valves returned to their seats by laminated springs. A single camshaft operated the valves through the medium of rockers; there was also provision for a second camshaft to close the valves, but this was never used. A train of gears drove the camshaft.
H section connecting rods, and two-ring pistons were employed. A dry-sump lubrication was adopted, utilizing one pressure, and twin scavenge pumps.
The chassis frame was extremely low, and passed beneath both axles, the center section being very deep and tapering towards each end. The bottom of the frame was flat, and was the lower part of the car. Thomas had now abandoned torsion bars, and the front axle was underslung on semi-elliptic springs. Reversed quarter elliptics were used at the rear. Hartford friction-type shock absorbers were fitted all round.
Transmission was unusual in that the four-speed gearbox was incorporated with the torque tube, and pivoted from a chassis cross member in a ball housing in front of the box. This housing contained the universal joint, which was driven by a short shaft from a multiplate clutch only 6-in. in diameter. The torque tube was lowered in relation to the axle by spur reduction gears.
A very low and wide radiator sloped steeply bakwards, and was situated in front of the axle. An oil tank was slung beneath the radiator, and projected through the under shield for cooling purposes. All previous Parry Thomas cars were fitted with disc wheels, but in this case the new special was endowed with the fashionable Rudge wire type, presumably in the interest of rapid wheel-changing at the pits. Perrot-pattern brakes were used, and these had rather small-diameter ribbed drums.
The driver sat right down on the undershield of the car, the steering column being practically horizontal. Bodywork was unorthodox, and earned the name "flat-iron" for the car. It was exceptionally low, the top of the bonnet being 'way down below the top of the front wheels, and came out to the full width of the chassis, completely enclosing the radiator and suspension parts. An upswept scuttle was provided for the driver, who had a faired head-rest. A passenger could be carried at a pinch.
These cars had various alternative induction arrangements. There was provision for one, two or four carburettors, and drives at the front of the engine for one or two superchargers.

Out of the two original "Flat Irons" I understand that only one now exists, and this is in the UK.

This is the one which was fitted with a diesel engine and used to attack compression ignition world records.

I believe the owner managed to obtain the original engine and drive train from the second car which was broken up in Canada. From memory, the only missing item is a rear axle.

Originally posted by Peter Morley

Hasn't it just got aluminium covers fitted to the wheels?
They appear to be far too dented to be 'solid' disc wheels!

The wheel fixing would appear to be a center lock (Rudge Whitworth type) fitting as you would expect with wire wheels. And covers could have been fitted to aid streamlining.

Yes indeed. I should have looked more closely, but was on my way to bed with a quantity of nice red wine on board.

to add to the information on the engine's details.
From Brooklands. The Complete Motor Racing History. William Boddy. (MRP)

These cars had remarkable chassis-frames which gave them their very low build, the side-members passing beneath both front and rear axles, the front ends being sharply upswept as anchorages for the half-elliptic springs. Reversed quarter-elliptic springs were used at the rear, mounted on brackets above the side members, and the chassis-frame tapered to a point behind them to support the tail. The oil tank, the driver's seat, only 5 inches from the ground, and the steering box being high-set, as on the Leyland. The radiator was inclined backwards and cowled in with the springs and dumb-irons, and so low was this cowl and the bonnet that they were appreciably below the tops of the front tyres. So effective was the streamlining that Railton estimated that 60bhp was sufficient to produce 100mph.

The engine was a striaght-8 of 52 x 88 m, 1,494cc, with aluminium water jackets in pairs of two surrounding cast-iron (or as some references have it, steel) liners spigoted into the crankcase. As the minimum weight under Formula had been increased for 1926, Thomas used a cast-iron crankcase in order to gain rigidity, eight large inspection plates being incorporated along the sides. The crankshaft was built-up, ran in five plain white-metal bushes, had integral balance-weights, plain big-ends and was of the unusual 4-4 arrangement in which all the throws in one plane were at one end and all those at right-angles at the other end of the shaft. The conrods were of H-section and two-ring pistons were used. It was emphasised that this was in effect a large engine with tiny cylinders, designed to run up to 6500rpm. The actual dimensions of the crankshaft were: total length 27in, big-end journals 30mm x 32mm diameter, main bearing journals 23mm x 38mm diameter. The cast-iron cylinder head carried two large tulip valves in each machined hemispherical combustion space and a copper-asbestos ring effected a joint between cylinder and head, while rubber and linen rings separated the head from the water jacket, the head being pulled down onto the crankcase by threaded turnbuckles which had holes to accommodate a tommy-bar. The valves, each of which weighed 1.5oz, were actuated by a spur gear-driven oh camshaft and massive rockers and closed by leaf springs, the layout following Thomas' usual practice, although the possibility of a superimposed camshaft to provide positive valve closing was foreseen.

Lubrication was on the dry-sump system using separate scavenge and delivery pumps. Two Roots superchargers were mounted at the front of the crankcase and cooled from the engine cooling system. To assist the low-set radiator a water tank was located under the scuttle. The drive passed through a special multi-plate clutch evolved by Thomas, which was only 3.5in in diameter and contained a large number of steel and Ferodo-lined plates. An open shaft with a single very large spherical universal joint supported in a phosphor-bronze housing took the drive to the 4-speed-and-reverse gearbox mounted on the front end of the torque-tube. This gearbox was distinctly robust and had its constant-mesh gears at the back. The rear axle contained a double-reduction gear to accommodate the low transmission line and was fully-floating. Thomas was said to be experimenting with a David Brown worm final drive with its own oil sump to obviate the loss of power through excessive oil-drag. Wire wheels were used, sometimes covered by discs, and the four-wheel brakes, operated by pedal and hand-lever from rod-and-cable linkages outside the car, had ribbed drums and Perrot-actuation at the front. The driver sat on the offside beside the propeller-shaft, with a cutaway in the cockpit on his left - useful for his elbow - and the tank was in the tail, its filler tunnel protruding from the scuttle cowling.

Apart from the two cars, Thomas was also having a boat prepared for the Duke of York's Trophy, to accommodate one of his engines.

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Welsh Motor Sport History

did the car race on the "continent" in 26-27 or just at brookland,

Only at Brooklands, although they were entered for Dieppe in 1926 but weren't ready.

And by March 1927 Parry Thomas was dead. So the cars didn't get developed to their potential.

Quite an amazing car for the time.

Originally posted by MCS
Dick

Have you tried writing to Bill Boddy?

I suspect he would have some information.

Cheers
Mark

See post 12

The best source for information on the "Flat Irons" is an article WB wrote for Motor Sport magazine in (I think) March 1973.

The following are extracts taken from a letter written to Veteran & Vintage magazine in 1962(again, I think!) by the owner of the survivng car: -

".....The remains of the ex-Munday car came into my possession in 1957....I was able to trace the car which went to Canada. This was broken up in about 1950 but the engine, clutch, gearbox, supercharger, and numerous engine spares have survived, and I have just had them shipped over....the only major components now missing are the torque tube and back axle."

I believe the car is still in the same unrestored state as it was around 40+ years ago, but at least it survives reasonably complete !

I thought to myself “I will leave it a couple of days to see whether any body responses” only to find 25 responses and a definitive answer in about 16 hours. I should have tried here earlier.

Thank you to all who responded and added to our knowledge of these cars. Especial thanks go to Robert Dick for providing the dimensions, of just about everything and Vitesse2 for the colour. I would believe Michael Turner as well!

I have a plan of the contemporary Delage that won both the British GP’s at Brooklands in 1926&7; in 1927 they were 1-2-3 with the rest nowhere. It had a 98.5” wheelbase and 53” track, so if Parry Thomas had continued his “lower” theme into “shorter” and “narrower”, which is logical, I think, the dimensions in Omnia can be trusted and certainly as close as we are going to get. I have my documentary evidence!

I think between you, you have posted just about every picture that exists of the Thomas Special GP cars, certainly every one I have got. The disc wheel covers were installed for a record-breaking attempt as Parry Thomas broke the hour record for 1500cc cars with in 1926 at 112.77mph, because that is what the caption under my copy of the picture Doug Nye posted says!

One of them also had a 2.7l Perkins diesel engine installed for record breaking in 1935.

I now feel doubly inspired to build a model of this car. I almost feel I owe it to you all. It will be for an event in the middle of August so it won’t be straight away, but I will post some pictures of it when it is finished. I have to complete a Cunningham Le Monstre for a race in May first …….. which is a different very different beast!

Thanks again.

Originally posted by Steve L
The best source for information on the "Flat Irons" is an article WB wrote for Motor Sport magazine in (I think) March 1973.

Correct, Steve: four pages, including several pictures not seen here.

Originally posted by Vitesse2
Only at Brooklands, although they were entered for Dieppe in 1926 but weren't ready.

Do you mean Boulogne?

I think the first 1.5 formula produced one of the most intriguing 'if only'. Imagine if the cars built for that formula could have been pulled together, in developed form, for a set of races. The Thomas Special, the Alvis, Fiat 806, Delage, Bugatti, Itala, Miller - let alone the designs that were half built or conceived (there was some strange French car, Sima? and the Salmson s8 of 1928 could have been extended to a 1.5 litre (the possible inspiration for Jano's 8C motor) had the formula still existed into 1928, as it should. The two litre era as well. Both seemed to be bursting with potential, but it just never quite came together at the same time. A real shame as the Thomas looks to have been brim-full of advanced and experimental engineering, as did so many cars of the time. Wonderful stuff, and thanks to everyone who has contributed.

Originally posted by angst
I think the first 1.5 formula produced one of the most intriguing 'if only'. Imagine if the cars built for that formula could have been pulled together, in developed form, for a set of races. The Thomas Special, the Alvis, Fiat 806, Delage, Bugatti, Itala, Miller - let alone the designs that were half built or conceived (there was some strange French car, Sima? and the Salmson s8 of 1928 could have been extended to a 1.5 litre (the possible inspiration for Jano's 8C motor) had the formula still existed into 1928, as it should. The two litre era as well. Both seemed to be bursting with potential, but it just never quite came together at the same time. A real shame as the Thomas looks to have been brim-full of advanced and experimental engineering, as did so many cars of the time. Wonderful stuff, and thanks to everyone who has contributed.

Hear hear - a really fascinating thread.

Now then, let's hear about Smith-Clarke's straight-eight Alvis, front-wheel-drive, 1.5 litre Grand Prix car - complete with horizontal valves!

PdeRL

Originally posted by Roger Clark

Do you mean Boulogne?

Yes I must have boarded the wrong ferry ....