604 w/ 8hp pulley question

[stellardtg11 25]

Really silly but simple question here.  Like the title says, I have a 604 (4 speed, no high/low) that I put a K181 8hp in.  Engine has appropriate 2.5" 3 groove drive pulley.  Sort of like the idea of putting a newer 4" drive pulley on the engine, streamlining things between my small collection, as well as having the tapped holes in case I ever need to remove pulley.  Silly question is if the original transaxle is okay with a little more speed, not that I'm going to be racing around or anything (this tractor is the one with a plow).  Or if it would be smart / necessary to swap the input pulley on the trans as well.  Thx !!

[ebinmaine 77,111]

10 minutes ago, stellardtg11 said:

little more speed

 

You may be in for a faster ride than you realize..

 

Going from a 2 ish inch pulley to a 4 inch without changing the transmission end is a pretty dramatic increase.  

 

OE high speed was around 6.2 to 6.4 MPH. 

 

Trina had a 4 to 4 drive on her Military Tribute Tractor because of a temporary engine swap. It did well over 10 MPH. 

 

 

10 minutes ago, stellardtg11 said:

question is if the original transaxle is okay

 

The transmission will be fine. 

 

You'll need to modify the engine end of the belt guard because that's your belt GUIDE which is a needed component.  

 

 

 

11 minutes ago, stellardtg11 said:

more speed, not that I'm going to be racing around or anything (this tractor is the one with a plow).

 

 

What's useful to you can only be determined by you. 

Here we have mostly rough terrain. 

Even 6 MPH is rarely used. 10 + was useless.  

She swapped back to the small pulley with the next engine.  

 

 

[stellardtg11 25]

26 minutes ago, ebinmaine said:

 

You may be in for a faster ride than you realize..

 

Going from a 2 ish inch pulley to a 4 inch without changing the transmission end is a pretty dramatic increase.  

 

OE high speed was around 6.2 to 6.4 MPH. 

 

Trina had a 4 to 4 drive on her Military Tribute Tractor because of a temporary engine swap. It did well over 10 MPH. 

 

 

 

The transmission will be fine. 

 

You'll need to modify the engine end of the belt guard because that's your belt GUIDE which is a needed component.  

 

 

 

 

 

What's useful to you can only be determined by you. 

Here we have mostly rough terrain. 

Even 6 MPH is rarely used. 10 + was useless.  

She swapped back to the small pulley with the next engine.  

 

 

Thank you for your input, great info!!  Figured it would be relatively inconsequential to the trans other than speed, maybe make 3rd gear useless if only putting a 4" drive pulley on, but I haven't messed with any trans yet other than fluid replacement.  Great food for thought thank you !!

[ri702bill 11,166]

Two things come to mind...

You NEED to keep the belt guard for proper clutch, brake, and shifting actions. The larger drive pulley may not allow you to.

The OE setup underdrives the Unidrive, primarily to increase torque... which you WILL need for plowing. If you increase ground speed you proportionally kill of torque. And the opposite is true...

[Ed Kennell 44,710]

You should see a 1.6 increase in speed.

Edited 2 hours ago by Ed Kennell

[squonk 45,390]

Trans gears are straight cut with no syncro's. Bearings if original have quite a bit of "run in time on them" If increasing speed you can expect an increase in transmission noise. 

[wallfish 19,087]

You could keep the same engine pulley and reduce the size of the trans input pulley to accomplish the same thing, and that way you won't need to modify the belt guard. But you will need to change the belt length either way you do it. Seems like what you're doing, going an inch smaller on the trans pulley would enough.

Yes, you can shift down to using 2nd and or 1st gear to regain any lost torque for pushing snow. Use 3rd gear as the speed travel gear.

An already good trans can handle it easily.

[Ed Kennell 44,710]

2 minutes ago, wallfish said:

reduce the size of the trans input pulley

Don't know if it matters, but  the larger pulleys would have more belt/pulley contact reducing the chance for slippage.

[wallfish 19,087]

Just now, Ed Kennell said:

Don't know if it matters, but  the larger pulleys would have more belt/pulley contact reducing the chance for slippage.

It certainly can matter! The trans pulley when reduced by only an inch should still be big enough. The engine pulley is smaller than that. Go too small and it will slip. The 1/2" belts like a 604 has do grip a lot better on smaller pulleys than a larger 5'8 belt would because they bend tighter more easily.

I've had trans pulleys down very small and they slip so had to add an idler pulley at the F plate on the frame to increase the belt to pulley surface area contact. Still had the unmodified original belt guard. 

[stellardtg11 25]

11 minutes ago, Ed Kennell said:

Don't know if it matters, but  the larger pulleys would have more belt/pulley contact reducing the chance for slippage.

Makes sense.  For what it's worth , having put this 8hp in the tractor seems to have the belt run a bit loose , and the more recent snow we got was just too much for it.  I don't know if the geometry from the factory vs. putting this 8hp in may have made the crankshaft be just a tad lower and / or back , just enough to make the belt run sloppy , who knows.  Rolled out and measured on hardwood floor the belt is not stretched out and measures exactly the length it should.  I had too wide of tires on the rear , no weight , and it seemed that I got bogged down but wouldn't even turn the rear tires once I got bogged down , even leaning back and rocking side to side like doing what worked for me with our first snow.  So it's still in a developmental stage and a lot of tweaking to do.  Thank you all again for input !!  Recalculating here.  Also going to go cut some big lead bars i forgot I had to go in the tray under the seat !!