Balancing Crankshafts With Air-Turbines 



IN the early days, when the problem of 

 the automobile manufacturer was to 

 make a car run at all, rather than run 

 economically and smoothly, balanced 

 crankshafts were unthought of. But as 

 the buying public 

 began to demand 

 cars with smooth- 

 running engines, in 

 order to reduce the 

 unpleasant effects 

 of excessive vibra- 

 tion, the automo- 

 bile engineer had to 

 devise some method 

 of equalizing the 

 power impulses 

 transmitted to the 

 driving shaft of the 

 automobile at each 

 cylinder explosion. 

 And so he hit on 

 the method of 

 weighing all the pis- 

 tons and connecting 

 rods, and classifying 

 them according to 

 their weights, in or- 

 der to be sure that 

 the reciprocating 

 mass of each cylin- 

 der was equal to 

 that of any other 

 cylinder in the same 

 engine. 



But balancing 

 the crankshaft 

 was a far more diffi- 

 cult problem, since it 

 is in one integral piece 

 which serves all the 

 cylinders of the en- 

 gine. In the old days, 

 the only way to dis- 

 tribute the weight of 

 the crankshaft prop- 

 erly on all the cylin- 

 ders of the engine was 

 to get it in static 

 balance, which means 

 in such a position that 

 when placed on two 

 knife edges, one at 

 either end, the shaft 



The Air-Turbine In Action 



The crankshaft is carried on two pivoted stirrups, 

 thus leaving it entirely free to turn about its axis 

 without being affected by its mechanical means of 

 rotation. The turbine wheel, which has six spoke- 

 like arms, each with a flat blade at the end, is 

 turned by a jet of compressed air issuing from a pipe 

 on a level with the highest position of the blades. 

 Two micrometers, in contact with the ends of the 

 shaft, show the vibrations of the shaft if it is out of 

 balance, and small weights are then attached to the 

 shaft by spring clips as shown. These indicate at 

 exactly what points metal must be cut off in 

 order that the shaft may be balanced perfectly 



The turbine when not in motion. 

 Its mechanism is clearly indicated 



428 



would remain in that position without 

 revolving. 



While this kind of balance was easily 

 obtained by the trial and error method of 

 turning the shaft and then cutting off 

 portions of the 

 crank-arms to make 

 the shaft balance, 

 it did not neces- 

 sarily follow that 

 either the engine or 

 the shaft would be 

 balanced when it 

 was rotated, as when 

 turned in the en- 

 gine* itself. Two 

 equal weights on 

 either side of the 

 center will balance 

 well even though 

 one weight is all on 

 one piston and the 

 other all on an- 

 other. Unequal 

 distribution makes 

 no difference. But, 

 nevertheless, the 

 piston to which the 

 heavy weight is at- 

 tached will push 

 down with a harder 

 force at each revo- 

 lution than the one 

 next to it. Hence 

 the engine runs un- 

 evenly, even though 

 the weights are bal- 

 anced. Excessive 

 vibration is set [up, so 

 that the engine wears 

 out quickly, and the 

 passengers are con- 

 stantly jarred and 

 shaken. 



The demands of the 

 American automobile- 

 buying public for 

 smoothly-running cars 

 has necessitated the 

 development of some 

 simple method of bal- 

 ancing the crankshafts 

 of such engines at a 

 rate which will not 



