Thornycroft "K type"

[mammoth]

If I may indulge the moderators I have created this topic in the hope that more information concerning the Thornycroft K type, otherwise known as the WD subsidy truck, built between 1912 and 1914. This model was very similar to the early 'J' type of which only two survivors are known - see Aussie Thornycroft topic - which in turn is naturally confused with the subsequent and more familiar war time and later 'J' type with disc wheels.

I invite all contributions and corrections.

The only manufacturer's illustration that I have come across is here;

http://archive.commercialmotor.com/page/29th-january-1914/12 where is was displayed at the Manchester Show.

During the first decade of the twentieth century Thornycroft were keen to put their products in a good light with the War Office/War Department. It wasn't just steam and internal combustion vehicles that they produced but naval vessels as well. Accordingly the company made a significant effort to meet compliance with WD design requirements.

The story of the various trials is much greater than can be covered here but were reported on by Commercial Motor magazine. The subsidy scheme came into being with a prescribed design criteria determined in 1912. The WD favoured a double reduction differential having been impressed with the Leyland rear axle (the same arrangement was used by Volvo and others into the 1970's) in previous trials, although chain drive was still accepted, albeit at a lower subsidy. Thornycroft, not wanting to take a competitor's design, designed  a completely double reduction arrangement which was granted a patent in Dec 1913.   http://archive.commercialmotor.com/article/14th-january-1915/20/patents-completed. The design was reported in Commercial Motor for the Olympia Show issue in June 1913...."run the propeller shaft horizontally to the rear, from a bearing carried in a special cross member to the top of the back axle housing, this shaft then gearing vertically below it by spur gears, which constitute the first reduction, the final reduction being by bevel in the usual way. "  The K type was the first to be granted a subsidy certificate and participated in the WD trials in 1913 and performed very well over the total of 1500 miles.  This design, would have made the diff housing very tall and I speculate that the unique raised cross members shared with the J were to accommodate this.

 

Edited March 25, 2021 by mammoth
typos

[mammoth]

The photo above is of my early J type which was equipped with a new design worm drive rear axle. The K type was reported as a new design in Commercial Motor in September 1912 with rating for gross load of four tons  whereas the J was rated at 3 1/2 tons. The K had larger wheels back and front and described as more robust but no detail is given of what the differences actually were. It carried the prescribed brush bar in front of the radiator and tow hooks back and front. The K type was inevitably significantly more expensive, more of which later.

[mammoth]

J K photos-001.pdfThe magazine article written by Bill Dawe back in 1994 now sheds more light on this model. Thanks to Bill's research back then I can now offer the below information.

The K model was designed specifically to meet the design wishes of the Mechanical Transport Committee of the War office. In addition to a double reduction drive axle a torque tube arrangement was required to control axle location, rather than relying on the springs, and so the rear axle and shackles front and rear which it's sister J model did not have. The first K was chassis 1177 sold with a subsidy to Pickfords on 24/10/12 and was shown at the 1913 Olympia Show. A total of just 60 K types were built with 26 going to private hands.and the remainder to the War Office. Towards the end of production the M4 motor was fitted randomly and then as standard and the last one was chassis 2206.

The transition to the WD version of the J model followed the War office recognition in 1914 of the failure of the subsidy program due to the onerous and expensive specification. ( Commercial Motor was scathing of the "subsidy muddle" and Johm E Thornycroft complained publicly)  The rear axle specification was dropped and so Thornycroft immediately submitted a K model fitted with the J worm drive for approval. and from this point the K model ceased production.

Thornycroft were a major provider to the navy and so at declaration of war big orders came in. The firm gave priority of steel castings to the naval orders (all manufacturers at the time had trouble sourcing steel castings) and so the pressed steel wheels came into being, concurrently with a re-design of the  of the early J to become the WD. J model.  The chassis now had conventional rear cross members, front axle shackles at the rear of the springs, steering tie rod to behind the axle, and petrol tank moved from under the seat to the fire wall. A new radiator which was lower and fitted between the chassis rails was introduced, although old stock high radiators continued to be fitted in  early batches.

J K photos-001.pdf

Edited April 9, 2021 by mammoth
addition

[mammoth]

Correction as I haven't worked out how to edit.

VCV magazine 44 has an article by Bill on Thornycroft engines and it is No 52 which has the article on J & K types.

[mammoth]

K type front.pdfFurther research has found what may be the only surviving image of Thornycroft's double reduction rear axle. The images from front and rear show the banjo style casting which cradles the gear casing. The torque tube can be seen attached to the top of the casing. The raised "set frame members" can be seen either side of the silencer.

K type diff.pdf

The front of both the J and K types wore a badge on the radiator with the legend "Thornycroft motor'.

Edited April 9, 2021 by mammoth

[mammoth]

Just why a model specially designed for the British subsidy scheme and more expensive (750 pounds vs 685 for the J) should be sent to Australia is a mystery. Chassis 1198 built 10/04/1913 was sent to McGhie Motors in Brisbane. Four other K types were sent to Australasia  one in January and three in June 1914.

[mammoth]

The strange radiator protector on the McGhie's K type was not a one off as seen on the Whitbread's K type subsidy model.

[mammoth]

Here is the 1912 catalogue for both J and K types. How the K got to be rated for a higher load than the J  was something to do with having larger wheels, which are close to the later standard sizes of 720 front and 850 rear versus the J which had non standard sizes possibly of their own manufacture. The extra 5 cwt of weight of the chasssis could be accounted by the special differential, torque tube and larger wheels but also possibly heavier springs.

catalogue J.pdf