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How to make a racing lawn mower (Updated!)

Step 10Updates.

Its been a year since this mower was completed. After a year of racing I've learned what the weak spots were on the machine. First, stock pistons in Briggs flathead engines do not hold up well under stress. I wound up blowing two engines early in the season when the rods snapped. So the first improvement was in purchasing a billet aluminum rod and a lightweight magnesium piston. So far this rod has held up well under the stress.

Secondly, any nuts and bolts that can come loose will come loose unless they are secures using nylock nylon lock nuts and loctite ( the blue bottle). Otherwise the severe track vibration will cause things to fall off, which they did frequently. So spend the few extra dollars and secure everything down and save the headaches.

Lastly, the cheap stamped bearings I went with in the steering system have way too much slop in them. I replaced all 8 of the bearings with sealed ball bearing units with steel snap rings. This removed all of the slop in the steering and made the handling much more accurate and responsive, which in turn is much safer. So make sure and invest in better high quality bearings for everything that moves.

Oh yeah- one more thing- Orange was not a good color. So now it is all-black.

The video is of our first event of the year. Enjoy!

pv_mower_racing_playdate.mp44 MB

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20 comments

Sep 14, 2009. 7:40 PMdieselman2013 says:

Hey, Were did you get your magnesium piston and aluminum rod? Im working on my race mower for a shop class project, to race at the county fair. Thanks.

Sep 15, 2009. 7:18 AMmowerracer (author) says:

I got both of them from a small shop called EC distributors. Here's a link to their parts:
http://www.eccarburetors.com/store/index.php?main_page=index&cPath=136_138

Dec 8, 2010. 7:16 AMJOHNTHEREDNECK says:

how would i put a fuel pump carb on my 12hp briggs i/c ? carb is off a 18hp briggs vtwin i blew up a few months ago :). where deos the vacum line go / what do i do with it. help please.

Dec 8, 2010. 12:56 PMmowerracer (author) says:

The 12HP briggs didn't come with a fuel pump so there won't be a vacuum line for one. The best bet for an engine like this is to make sure your gas tank is elevated far enough above the engine to give you proper gravity.

Dec 28, 2010. 2:23 PMJOHNTHEREDNECK says:

could i run the vaccum line off the intake would it have enough vacum to do it ?

Dec 12, 2010. 12:44 PMJOHNTHEREDNECK says:

i know, i just want to know if it can be done because Ive got the set of skills to do what is necessary what is it just a plate with a hose fitting connected to the pcv?

Oct 10, 2010. 6:00 PMrilley1313 says:

hey where do you get all of your part/components

Oct 13, 2010. 8:04 AMmowerracer (author) says:

The steering components came from Acme Mowersports ( look them up online) , EC distributing, and Ebay. A great many components are actually go-cart parts.

Jan 2, 2011. 2:10 PMJOHNTHEREDNECK says:

how much did it cost you .

Sep 16, 2009. 1:33 PMdieselman2013 says:

Thank you.

Sep 1, 2009. 3:12 PMMerkatroyd says:

Thanks for going through the trouble to make this detailed tutorial. I've been building my lawmower for a while now, a year, occasionally taking breaks from working on it, so It was alot slower than your build. but it was very fun! my mower is an old craftsman mower, which is bigger and heavier than your mower (so yours can probly whip mine lol) but it's almost finished. I just need to find somewhere to mount the battery, and hook up the throttle. It's going to be fun. oh, and uh, by the way, I have a few questions: How big of an advantage do 12 horsepower engines with overhead valves have over flatheads? I have an engine just like yours, except it's a tecumseh, and has overhead valves. I THINK they breath better, and therefore rev higher. I know they do for cars. Would it be a good idea if I took an 18 horsepower engine and swapped it? If I have a centrifugal clutch which is rated at a maximum of 12 hp, would it last if I used it on the 18 hp motor? plus, I have some questionable parts. I have one pulley which has a big chip off of one edge next to the belt. would It damage the belt? I got a RAGB just like yours. I took the little sheetmetal cover on the side off, and one of the gears are missing a tooth!! would this fatigue the gears? do I need to take it out and replace it? what would be a good source for pulleys? I didn't use chains like you. and I can't seem to find a pulley more than 5" wide. well, thanks again, I hope my questions didn't sound long-winded, amateurish, or confusing.

Sep 1, 2009. 4:52 PMmowerracer (author) says:

You can do just fine with a smaller engine. There's one guy I know of on our forum who races with 5HP go-cart engines and he beats guys with much larger engines. The trick is spending some time getting the right parts and the right setup. I can spin my flathead much faster due to the performance rod, piston, and flywheel. The flywheel is much lighter, thus much better torque. As far as pulleys, well yes you could possibly damage the belt with it. I look on Mcmaster car and a site called cheapmowerparts.com for pulleys. They're usually not too much money. Go for steel or cast iron since aluminum pulleys will split due to the pressure and heat. As far as the RAGB... I suppose you could just go until it blows. Its hard to tell what will happen. Its generally not a good idea to go with a cracked gear. I guess what you'll need to consider is what would happen if it did blow, which is would it cause the mower to stall out suddenly, which could throw you off. Just be careful. As far as the clutch, 18HP might be pushing it a bit. Mine is rated for 10 HP and I'm using it on a 12HP engine and it seems to do fine. But 12-18HP might be... pushing it. You could try it and if you smell burning, then its time to consider another clutch. good luck!

Jun 7, 2009. 4:26 PMjoecrap says:

Why was Orange not a good Color? I was going to go with Yellow, or some other "bright" color.

Jun 8, 2009. 7:51 AMmowerracer (author) says:

Nothing wrong with orange, I just wanted to do something different this year. Luckily, you can paint your mower whatever color you want and its legal.

Aug 14, 2009. 9:55 PMtj1796 says:

hay man wat kind of mower do u have an do u no were i can get one from

Aug 17, 2009. 7:44 AMmowerracer (author) says:

The mower was a Grants, but the company went out of business a long time ago. You can generally use just about any mower. This instructable just gives you some ideas on how to modify mowers for racing.