basic pulley math - am I on the right track?

[Pullstart 62,780]

So I'm working on hooking up a "late model" tiller to my 502.  Based on drive pulley difference of my 502 (now 8 hp / 8 speed) and my 8 speed donor c-101, I've come up with this data:

rear tiller pulley is 9.5"
another pulley I have is 6.5"

pi * 9.5 = 29.83
pi * 6.5 = 20.41
difference of 68.4% circumference roughly

drive pulley of c-101 is 4.5"
drive pulley of 502 is 2.5"
using the same formulas, difference of 55.5% circumference roughly

with that 6.5" pulley mounted on the tiller, I'd be at about 80% of stock drive speed.  is that correct?  if so, I should be able to perform alright if I drop down a gear.  Without changing any pulleys, I figure I'm about 55% of drive speed.

I just don't want to buy a belt just to be unsatisfied with the performance of the larger pulley.

[gwest_ca-(File Mod) 11,031]

I take it you are just working on the tiller tine speed.

What about your ground speed? The 502 is too fast at the rpm required to drive the tiller. Even 1st gear at an idle is too fast. A low range 6-speed transmission or a speed reduction kit may be in order.
http://www.wheelhorseforum.com/files/file/499-speed-reducer-1964-1966-sr-64-om-ipl-a-7140pdf/

Garry

[stevasaurus 22,705]

Garry, I think his math is correct, and it sounds like he has an 8 speed tranny with an 8 hsp (from a C-101) on the 502 frame.  He said he had a late model tiller...so with the new trans and the new engine...he really should not have to change anything. The only difference is the frame and wheel base.  My only question...wouldn't a C-101 have a 10 hsp Kohler?? 

[Pullstart 62,780]

thanks for the input guys, I appreciate anything I can get!  I did toss in an 8 speed so with low range, I have a feeling I'll be plenty slow to let the tiller dig - as long as I have the tiller speed turning.  the engine is a K181T from a belt driven air compressor so I think power shouldn't be an issue with the crawl ratio of low range.  so it'll still spin slower than if it were on the c-101, but if math is correct I guess it'll do. 

[slammer302 2,155]

I think the 8hp will do just fine if you take it slow I have a friend with a B-80 with tiller and he gets the job done

Sent from my XT1080 using Tapatalk

[Pullstart 62,780]

cool, thanks Slammer

[gwest_ca-(File Mod) 11,031]

4.5" engine pulley divided by 9.5" tiller pulley = 47.37%

2.5" engine pulley divided by 5.278" tiller pulley = 47.37%

I use a Roper tiller that has it's own 8hp engine with a 3" pulley and a 6" on the tiller. They went with a pair of belts I suspect because of the short contact area on a 3" pulley.

Garry

 

Edited September 18, 2015 by gwest_ca

[tim.bergfeld 0]

Wow I have a pulley questions too don't wanna high jack your thread

[Pullstart 62,780]

well my 6.5" pulley was the wrong size so I have a new one on the way from ebay... then measuring for a belt and getting tension all set!  look out garden, red's coming.  I guess I'll have to get some time to get a few truckloads of manure this fall!