312-8 Pulley Wheel Question

[allen9878 6]

Afternoon!

 

I am looking to adjust the diameter of the pulley on the engine and the one on the transaxle to speed up my tractor a bit. (For fun)

 

I have decided to increase the size of the engine pulley by 1" and decrease the size of the trans pulley by 1". I have not been able to find the proper pulley in local stores, and am hoping anyone here might have some insight into where I could order them online, and maybe help me identify the proper side as I'm not exactly sure what size is on there currently (Do you measure the outer diameter of the pulley, or the inner diameter of where the belt lays? Base on outer diameter, they are 4" on the engine, and 6.5 inch on the transaxle.)

 

The tractor is a 312-8 1985, with a 4 pinion 1" axle shaft transaxle. I greatly appreciate any feedback or help!

 

Thanks!

 

-Bert

Edited July 28, 2017 by allen9878

[953 nut 57,839]

            I am not a big fan of swapping pulley size to "make it go faster" as there are several side problems that need to be considered. The brakes on a  were not designed for stopping at high speeds and the belt guard, clutch and accessory belt guidance components were engineered to work well with the factory pulleys. If you plan to use the PTO to drive a mower or other attachment you will need an engine pulley that it can be bolted to. Unless you want to put yourself through a lot of unnecessary aggravation for a minor increase in speed I would recommend leaving it alone. Rather than a top speed of 4.3 MPH you would have a speed of a bit over 5.

[cschannuth 3,817]

I agree with most of what 953 Nut says. If your going to do more than ride around on your machine, getting the PTO set up correctly is a pain. Also, the belt guard will need major mods to allow the transmission to operate.  Especially if you change both pulley sizes. 

 

The one thing I may disagree with (sorry) is the gain in speed. I had a 606 roller that I put a Predator engine in. I increased the engine pulley from 2 1/2" to 3 1/2" and now it runs 8.3 mph according to my gps. In that case I just had to trim the belt guard a small amount near the engine pulley. 

[953 nut 57,839]

1 hour ago, cschannuth said:

disagree with (sorry) is the gain in speed.

Don't be sorry, I was sort of shooting from the hip on the speed. I did the math based on the 4"/6.5" vs. 3"/7.5" given by @allen9878  and 4.3 MPH from the manual for a 312-8 and came up with 6.61538 MPH.   

[cschannuth 3,817]

30 minutes ago, 953 nut said:

Don't be sorry, I was sort of shooting from the hip on the speed. I did the math based on the 4"/6.5" vs. 3"/7.5" given by @allen9878  and 4.3 MPH from the manual for a 312-8 and came up with 6.61538 MPH.   

 

Lol.  I just didn't want to sound like some kind a know it all. Believe me, my wife reminds me all the time that I'm not as smart as I think I am. 

 

 I was actually very surprised I gained over 3 mph with the front pulley change. By the way, I was assuming that the existing pulley was 2 1/2 inches because that's what my 701 and 857 both have on their original Kohler engines. 

 

It would really be nice to have the high/low range transmission with the extra speed. I've always thought low range was too slow to be useful. 

[953 nut 57,839]

11 minutes ago, cschannuth said:

wife reminds me all the time that I'm not as smart as I think I am.

Don't they all?    

[Ed Kennell 40,455]

All this high tech pulley math has my noggin spinning.  

Tractors are made for working.

If you want to go fast, build one of these.

 

 

[allen9878 6]

All good things to think on!

I don't plan to do anything with the pto, I purchased this for $50 and it will be a mud runner. I'm currently replacing the axle bearings so its a bit in pieces right now, but I'm locking the rear diff and will hopefully be back to running within the next week as I have spare time. 

[cschannuth 3,817]

1 hour ago, Ed Kennell said:

All this high tech pulley math has my noggin spinning.  

Tractors are made for working.

If you want to go fast, build one of these.

 

 

 

This is sorta my hybrid worker/racer on a budget. 

 

[Shooter67 22]

Its been years but i did it to my 312-8. Changed the rear only, to much of a headache to do the front engine pulley. I went down to a 4 inch pulley and it increased the speed quite abit! No major mods required. Hardest part was finding a belt but theyre easily had at Rural King and places like that nowadays. Went to my local mower shop and found the pulley new. Wasnt a WH part of course, not quite sure what it was actually made for haha

[ericj 1,578]

I did something similar to a 89 416-8 I have, but did it the simple way, sorta. I did an engine transplant with an 18 hp onan from a 518-H. I simply used the Hydro engine pulley which is a lot larger. had a tough time to figure out what size belt to use, but once done it worked pretty good. I don't notice much difference in low range and only slight difference in high first. in high second a slight difference which is what I was looking for, when I'm mowing, you know 2nd to slow and 3rd to fast. Well 2 is just about right now, the big difference was in 3rd high. It is a lot faster by several MPH. Do't have a GPS to measure, but you better hold on lol 

 

 

 

 

eric j