explain what good the 6 to 1 gear on small single piston gas engines is for.

[Rob-D]

One should be able to get the same increase in torque by using different size sprocket wheels, correct?
Say a 4 inch on engine and 16 inch on other sprocket wheel connected to tool being powered this would result in a 1 to 4 torque increase correct?
From 20 lbs to 80 lbs torque?
The only HP I need is to turn the sprocket wheels and the steel shaft with unblanced weight to shake the gravel screen cloth mounted on springs.
The commercial manuf. gravel screen plants have 12-13 hP small gas engines powering them, so I assume thats what I need to turn the steel shaft, which is mounted tothe screen plant shaker box via two pillow box bushings, one on each end of steel shaft. Two u-joints would connect 16 inch wheel to steel shaft to compensate for movement of shaft as it shakes the screen.

Work = HP, one HP = 550 ft/lbs/sec , it was defined by James Watt after watching a horse pull a load. The last part of ft/lb/sec is seconds and one HP can lift 550lbs in one second. When you reduce the speed of an engine by gearing it down you increase the torque, in your case 6 times to 3,300 ft/lbs in 6 seconds so, as JJ said, the HP stays the same but the torque goes up while the time to do the work (W=FD; work = force times distance) goes down. (3,300/6=550 ft/lb/sec.)
You are correct, you can reduce the motor by your own system and gain the same torque with the resulting reduced rpms. Manufacturers put gear reductions on motors for those implements that ran slowly but needed more torque with a smaller package (the internal gear reduction).

Rob

 

[J_J]

burntside bob,

You can gear up or down. It all depends on what you are trying to do. You can change the speed/torque by using gears, belt and pulley, chain and sprocket, cone drive. hyd fluid and hyd motor, and probably several more. .