HOW TO BUILD A RACING TRACTOR

Engine Pulley

            The most important change you can make is pulley changes. Most tractors have a 3 1/2" on the engine and anywheres from a 5" to a 9" on the rear end. Rear pulleys can be had for a couple of bucks at your local hardware store. You more than likely want about a 1.5 to 1 ratio front to back, but really it depends on how much power you have. I have a 5 1/2" on the front and a 3 1/2"on the back.

Transaxle with drive pulley and swing pulleys

 The clutches usually work by having pulleys that swing back and forth putting tension on or letting off the belt. You can see this by looking under your tractor as you push the clutch pedal.

The output shaft on most tractors are 1" with a 1/4" keyway. Most engine pulleys are a 1" inside diameter. Some old pulleys you can just take off and flip them. If you have trouble finding pulleys click on the links below.                

Here's a link for new front pulleys. http://www.mfgsupply.com/MowerPullHDCast.html/mv_session_id=6fdoIUni

and http://www.grainger.com/Grainger/wwg/start.shtml?BV_UseBVCookie=no   The Grainger site you need to type into the search field "v belt pulley 1"  bore" or what ever it is.

Also click on the belt formula link to figure the new belt size 

 In my opinion across the shift, 5 and 6 speeds are the best for this.  

They allow you to start in a lower gear and shift up as the gears wind out.

If you are building from the ground up, your best bet is to find a tractor with this type of rear. It's easier to change the engine and shim your front pulley than to try to shim the rear into alignment.  If you have a bad rear, you can get them at tractor junk yards or try Ebay. They have brand new 5 and 6 speeds. They can be had for $50 and up. You don't have to get the exact same one. There are a few manufacturers and are all pretty much the same, but, make sure you check the measurements.

Throttle lever

Throttles come in all shapes and sizes. Some people like a gas pedal type on the running board. While others like a lever on the steering wheel. I like the levers. You can use brake levers or a atv throttle works good too. Mine is a Harley Davidson brake lever with a bicycle cable. Lever or pedal they all hook up at the carb something like this.

Throttle cable coming in from the bottom

Note the way the cable is clamped at the bottom. Also note the extra return springs, they keep the throttle from sticking. The end of the cable is attached by a nut and bolt with washers on it clamped to the existing linkage.

Exhaust with chrome tip

Exhaust changes can be fun. If you do it right they improve performance and make 2 cylinders sound like a Harley with drag pipes. My exhaust is the old pipes cut off short flipped around and bolted back on. I then forced some 1" threaded pipe into it and ran elbows under the deck.

I then clamped it to the deck and put a piece of chrome sink pipe on the end for looks. 

Length of pipe is an issue. Too long, too much backpressure. Too short, and too little. A good way to do this is. Put a long piece of pipe on and paint it white, let dry. Start up the tractor and let it run. Cut it off where the paint stops burning off this is about the right length. Remember to make it a little shorter if you add elbows. Usually 15" to 25" depending on the size engine and how many turns you have.

Sometimes changes in pulley size changes the path of the belt, and it's necessary to put an idler pulley in. The one I had to use came from a Jeep smog control idler setup. I just bolted it to the frame. 

Here is one to give me a little more tension on my belt when I'm racing, but keeps the tension off the spring when not racing.

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