In my time as a lawnmower mechanic I have accrued, mostly through trial and error, the knowledge of how to make a lawnmower run quite a bit faster than the factory speed. I would like to share the knowledge I have with you, while also reminding the reader that you will undoubtedly have to go through the same trial and error type learning that I did. This in mind we may now proceed to the process of building a racing lawnmower.
1. Selecting a Lawnmower
To be a candidate for a racing lawnmower a mower must be belt driven and have a manual transmission. Hydrostatic or zero turn transmissions will not work. In order to be a practical choice a mower should be cheap.The best way to get a cheap mower that will work for a racer is to find a mower with a damaged deck, or an older mower that is impractical to cut grass with, but still has a good motor and transmission
2. Building the Mower
The first step in building a racing lawnmower is to remove the transmission. This is a simple task and will make it much easier to change the pulleys on the transmission. The most common type of transmission is a Peerless, which is made by Tecumseh. To take these transmissions out first disconnect the linkage to the shift lever. This is as simple as removing a pin or nut where the linkage connects to the transmission. Next you will need to remove the four bolts that connect the transmission to the frame. Now that the transmission is free you can give it some slack on the belt and take the belt off. The transmission is now free. To remove the pulley from the transmission you will need some penetrating oil and a wheel puller. You will take a snap ring off the top of the shaft and then use the wheel puller and a hammer to remove the pulley. Now you need to put a smaller pulley back in it’s place, this will gear the lawnmower to go faster. Most transmission shafts are 5/8″ bore and a pulley can be found at most hardware stores or machine shops. After replacing the pulley and putting the transmission back on the mower you must take the pulley off the motor. To do this take the protective screen off the top of the motor and hold the bolt on top of the crank. Next get a ratchet extension and take the bolt out of the bottom of the crank. A metal piece with two pulleys should now fall free. Again go to your local hardware store and get as large a pulley as you can fit between the frame. You will also need some keystock to make a key for this new drive pulley, and some hoseclamps to space it out.Also put a washer on top of the new pulley to keep it from contacting the bearing in the bottom of the motor. After this new pulley is on you should get a new belt to fit the new gear ratio. Now it is time to address the motor. the main thing that needs to be done is over riding the governor. There is a piece of metal on top of the carburetor that has a 90 degree bend in it, bend this straight and your engine rpm’s will no longer be limited. If you so desire you can also install a foot throttle. The easiest means to accomplish this is to bolt an old bicycle handbrake on the lawnmower footrest and use the old bike brake cable as a throttle cable by running it to where your old throttle cable went. The last thing to do is disconnect the brake. I know this sounds like a bad idea but you are going to have to shift on the go because of the new ultra high gear ratio. Because the lawnmower transmission is geared so low, when you are at speed letting off the gas will pull the lawnmower down fairly quickly. This eliminates the necessity of brakes, although some form of braking could be installed if you so desired. You are now finished with the building of the machine.
3. Riding the Mower
Now it is time to enjoy your new creation. A racing lawnmower of this caliber is not to be taken lightly however. Lawnmower steering and suspension technology ensure that driving one of these machines at the speed it can now attain is a white knuckle experience to say the least. Make sure you are in a safe area and can operate your machine competently before opening it wide open. Otherwise have fun and enjoy the fruits of your labor!
