1922.] The Shrawardine Tractor Trials, 1921. 977 



states, " both the maximum and sustained pull were less than 

 the tractors were capable of exerting under normal conditions 

 and on softer ground." Why this should have been it is not ea*sy 

 to say with certainty, although the hardness of the ground and 

 the difficulty of penetration with spuds doubtless is a factor. 

 The unsatisfactory nature of the results points to some modifica- 

 tion of the test, since they are clearly valid in respect only of the 

 exceptional conditions prevailing at the time and have no general 

 application. 



Mechanical Questions. — Engines. — The ordinary four- 

 cylinder engine appears now to be almost in full possession of 

 the field, bat there seems to be an opinion that the six-cylinder 

 engine may be introduced in the tractor on account of its 

 greater steadiness of pull. The two-cylinder horizontal slow- 

 speed engine still retains its position in some popular types. 



The Avance tractor was unique in one respect — it was the 

 only two-cycle hot-bulb engine for burning crude oil, and the 

 surprising cheapness of the fuel suggests that a more extended 

 use of this engine may be expected in the future. The Avance 

 had a certain crudeness of design, and vibrated violently on its 

 springs w r hen undergoing the test for belt horse -power, an 

 effect which was no doubt due to the inevitable unbalanced 

 forces of a single-cylinder engine. The irregularity of turning 

 effort, in spite of the heavy fly-wheel, seemed to be reflected 

 in the quality of the work done. The possibilities of an engine 

 of this type for agricultural purposes are well worthy of con- 

 sideration by manufacturers, and those wiio favour the slow- 

 speed power unit in preference to the high-speed type may 

 shortly be offered a further choice. 



Pulleys. — One of the principal functions of agricultural trac- 

 tors is to drive stationary machinery, and for this purpose they 

 are fitted with belt pulleys. The variety of methods in which 

 these pulleys are fitted is very wide. It is regrettable that 

 manufacturers seem not entirely to appreciate the fact that it 

 should be possible to manoeuvre tractors readily into any desired 

 position; this is especially the case when the drive is cross- 

 wise to the tractor. An instance occurred at the trials where 

 a machine took as long as 41 minutes to obtain the correct 

 alignment and as a consequence a time limit of 30 minutes was 

 imposed. Designers should regard the placing of the belt 

 pulley as being one of the most important subsidiary features 

 on a farm tractor. 



. B 



