Topic: New and want to make my tractor faster...

[grizzly812]

Hey everyone,
Im new here and I havent seen any guides or anything so im making this post to ask how to gear up my lawn tractor so that I can get about 25-30 mph and still have some low end.

I have a Murray lawn TRACTOR and its a 20 hp Briggs and Stratton v twin. Its got a 6 speed transmission and runs great and now ive decided to make it into a toy to play with around the neighborhood. The tires are larger than normal because its a lawn tractor, not sure the exact size off hand.

I have a pretty good technical know how with engines and what not, i can mig weld, and do other pretty advanced mechanical tasks. I hardly know anything about altering the gearing with tractors other than changing the pulley sizes.

First question is can I simply change the pulley sizes on the engine and transaxle to get more speed or will I burn something up internally in the tranny.

Next question is how do i get the pulley off? I have looked the rear axle pulley and it and its pretty well rusted and I cant see any bolts or anything holding it on. And do I need a special tool to remove the front pulley?

Also where can I get pulleys from to change the ratios. I have some pulleys left over from the deck of the lawn tractor but I know yall are buying them from somewhere and not scanvging through trash.

Thanks for your time.
Steven

[Squidd]

... I'm making this post to ask how to gear up my lawn tractor so that I can get about 25-30 mph and still have some low end.

First question is can I simply change the pulley sizes on the engine and trans axle to get more speed or will I burn something up internally in the tranny.

Keeping with your goal of 25-30 mph, just changing the pulley sizes will be your most feasible route...Check your tranny ratio in highest gear, (how many turns of pulley to get one turn of axels... then shoot for a 9:1 ratio by adjusting pulley size (9 turn of engine to 1 turn axle) most likely looking at bigger on the engine pulley and smaller on the trans pully..with the governor off or tweaked up you should reach that 25-30 easily in high gear and still have some decent low end pull...Splitting the case, switching out the old grease with new or gear lube, changing some of the bushings to bearings all will help in longevity...

Next question is how do i get the pulley off? I have looked the rear axle pulley and it and its pretty well rusted and I cant see any bolts or anything holding it on. And do I need a special tool to remove the front pulley?

Should be a snap ring keeping pulley on keyed tranny input shaft below all that rust... get clip off, "juice 'er up" and give 'er a pull...(or a tap or heat and beat with a BFH... :shock:)  

Also where can I get pulleys from to change the ratios.

Mc Master Carr or ACME mower sports...I believe George can hook you up thru EC Dist.... on line or most any small engine shop or even Hdwr store...... pulleys are standard 5/8" and 1" bore and easy enough to find...

[grizzly812]

I really appreciate the quick response. I think ive got a good understanding now of what I need to do.

More questions sorry I just thought of them. On my engine pulley, there is two pulleys (one for drive, one for blades) is it possible to take the larger pulley (blades) and move it to the top as my new drive pulley? Then get rid of the bottom pulley and shaft that extends beyond the drive pulley because it is just in the way.

And if so how do I get them off? (Sorry I know thats a lame question but I dont see anyway to get them off and dont want to break anything by hammering the crap outta them .)

Also to change the gear lube in the rear end, is this only possible by opening the case and then draining it and filling it back up. If so how much gear oil goes back in, fill to the rim?

Ill get my current ratios and pulley sizes tomorrow when its light again.

Again, thanks so much youre really helping me out here
Steven

[grizzly812]

O yea, totally off topic but o well...
Is it damaging to your engine to run straight exhaust pipes without a muffler? Like for example could I weld on some custom straight pipes, of length 2 ft or so, and scrap the muffler without having to worry about burning up exhaust vavles? I have heard that you can damage youre valve train by running open headers but dont know if this holds water (because I have seen many people run them with no trouble).
Thanks so much
Steven

[SilentNoise]

To get the engine pulleys off, there's usually a bolt on the inside of the shaft that holds them. Unscrew that and it should come off.

With my engine pulleys, that sucker was REALLY on there and we couldn't get it off for the life of us. I actually wound up mangling the lower pulley a bit (hehe... oops). After all of the frustration, we cut off the lower pulley and had to use a gear puller on the upper one (which screwed it up as well - not that I really cared though........ now this shouldn't that bad in most situations, but on occasion they can be a pain.


As for the transaxle, usually there's a screw on the top of the casing that you can undo if you need to top of the gear oil.

I find the easiest way to drain the transaxle is to open it up.... this way you can also inspect the guts for wear and tear at the same time, but that means you have to seal things back up when you put it back together.

[grizzly812]

Alright, thanks for the response. Ill probably try pulling the pulleys tommorrow and see if I can get anywhere.
Do you have a general recomendation for pulley sizes to get me at somehwere close to 30 mph, or do you need my current ratio to figure that out?

[matt25001149]

ok man go with a 5'' on motor and a 3.5'' on rear that should get you in the ballpark of wat your lookin for

[grizzly812]

awesome, thanks alot matt

[tory]

On that 6 speed to change the rear lube you will probably have to split it.Most likely it is full of a cheap grease rather than gear lube.Only way to change that is a complete tear down,You can change it over to gear lube and that will do a better job keeping it together,but they will leak,as it is not desighned to hold that thin of lube.  16 to 20oz should be enough.P.S.  Take it easy on the shifting,thats what kils them.TB

[bigbadmower]

i was just wondering were to get a big pulley to fit a 1 3/8" shaft i could only find a 2" pulley

[Squidd]

McMaster.com is one place...

[bigbadmower]

Thanks what type of speed could i look for with 6.25" front pulley 3.5" on bottom of jack shaft 4" on top of jack shaft and a 3" on the transaxle. I f the motor is running 4000 RPM.

[Squidd]

There's a math formula for that, but need to factor in tire size (circumference) and final drive (ratio) of trans axel to be accurate...

[bigbadmower]

running 18" tall tire and 9:1 transaxle

[Squidd]

57.79 mph...