35mph 633a?

I am wanting to build a Sears suburban mud tractor to keep up with ATVs at the Hatfield and McCoy trails. I wanted to know if there is an internal trans mod or what pulley ratio to use to get to 35 mph. Any ideas?

I used a 9 inch pulley to achieve around 30 with the Craftsman AYP variant of the Roper 633a.  It's possible to do more, but that would require cutting out the pulley hub from the transaxle as it is tapered.  Then welding that hub to a new smaller pulley.  I would also upgrade the ball joints to heim joints in your steering to make is safer.

@MightyRaze good call on Heim joints. I will look into a9 inch pulley for mine. Thanks!

633's are geared kinda low. I was looking for the gear ratios in high range because I checked them fairly recently. Can't seem to find it though. You can mark the rear axle and mark the input shaft or pulley, then count how many turns of the pulley it takes to spin the rear axle once in 3rd high range. Then you need to know your rear tire outside diameter, so measure around the outside of the tire. With that info, you can figure out what kinda pulleys you need roughly if you look online. It gets semi confusing but there's various calculators and things online you can use too. Figure like 4000rpm for the engine if ungoverned? 3600-4000 I'd say for max speed if you've got a stock engine.

I used a jackshaft on mine so that's more pulleys involved, but I'm geared for about 19mph. Just ended up that way, I didn't really plan it. @MightyRaze You used a 9" pulley on the engine? You got a belt clutch to work that way?

mr.modified wrote:

@MightyRaze You used a 9" pulley on the engine? You got a belt clutch to work that way?

Stock clutch with belt twist even!



But I digress. Back to topic.

Whatever you do...glasspack or straight pipe always makes it go faster

On another note...got pictures?

@Rustbucket Garage I don't have pictures because I don't have the tractor yet. The guy in trying to buy it off of won't respond to me

Yeah I hate it when people do that. Hope it works out better for ya!

Thank ya! Means a lot.