Bob Cat 371

[Miller1946]

Gentlemen

I am in the process of trying to determine the size of pully required on a 20 H.P. Honda gas engine that will suport my hydraulic pump rated at 5 G.M. at 3,000 RPM. The pully size on the pump is 5" and like I indicated I need to know the size of pully required on the motor.

The original motor was a Kohler which pooched on me so I put on the 20 HP Honda.
Any assistance you can provid me would be greatly appreciated.

Thank you.

Darrel

 

[cycle_gator]

What is the duty RPM of the motor? The relationship between the pulleys is linear and varies directly with the RPM difference although in the inverse. Say the motor runs at 2500 RPM, a 6" pulley will give you 3000 RPM on the pump with its 5" pulley, or mathematically 2500 is to 3000 as 5 is to 6, Make sense? Another way to look at it the circumference of the 5" pulley is 15.7", so in one revolution it travels that far. The six inch pulley has a circ. of 18.85. So in 3000 revs the 5" pulley travels 47,100" and at 2500 revs the six inch pulley runs 47,100.

Hope this helps

 

[J_J]

The Honda will probably run at up to 3600 rpm, so just cross multiply.

5 over 3000 is to what over 3600, and that is 6. So a 6 in pulley on the Honda will turn the pump at 3000 rpm.

If you have another 5 in pulley, for the Honda, just run the engine at 3000 and the pump will be turning at 3000 rpm.

 

[kennyd]

Welcome to TBN

Looks to me like you need a 4" pully. The motor RPM will be fixed at 3600, you already have one 5" pully, and need 3000 RPM for the pump.

Calculate here: https://www.surpluscenter.com/techhelp.asp?catname=hydraulic on the left side of the page, click on the Pully Diameter Calc.

There are plenty of other calculators available, just google "pully diameter calculator"