How to make a racing lawn mower (Updated!)

 Notice:
 I've recently completely turned this mower into a new build. If you've read this before, proceed to step 12 for the latest updates. Otherwise, start reading below for the original build. Thanks to everyone who has commented before. As always, feel free to ask questions and I'll do my best to answer. Click Here to proceed to step 12.

In this demo, you'll get some ideas of how you can make a real racing riding mower used in national events. Have fun turning what used to be the family lawn mower into a fire-breathing high speed racing machine. Also- I'm constantly making changes and modifications to the final machine so check back to see what I've done. The next plans I have include steering upgrades.

Please read the following paragraph before proceeding.

Before we start, there's a bit of safety to discuss.Yes, racing lawn mowers from an outward perspective is sort of funny ( which it is!)But its important to realize that racing mowers such as these are heavily modified to handle much greater speeds than the original mower was designed for. Many of these mowers go 50MPH or more.Making a race mower isn't as simple as taking a stock tractor and making it go fast without any alterations. So its important that the frame, brakes, steering, engine, and wheels are modified or altered to handle this additional speed.So to make this point doubly clear, it is NOT a good idea to take a bone stock mower and make it go fast. You can, and will get hurt if you do so, and trust me- I've seen enough people wreck due to this very reason. So play it safe. Secondly, if you do plan on racing, make sure and check out the rules for your chapter and wear appropriate safety gear such as a helmet ( motorbike), gloves, boots, and long pants.My mower is built using ARMA ( American Racing Mower Association) rules and regulations. Lastly, your mower must have an approved jet ski/snowmobile style safety tether switch. If you fall off ( which we often do) the mower must automatically shut down or it'll keep right on going! Racing mowers might seem silly, which it sort of is, but you can get hurt if you're not careful. So be safe!

Ready, let's get started! The 'victim' I chose for this build is a late 60's Grants mower. Tiny little mowers like these were produced back when riding mowers were still deemed a luxury. They're little more than a seat sitting on top of a mower deck. Most used smaller engines. The advantage of using such a little mower is that you can reduce the weight dramatically by simply having a 'legit' riding mower complimented with a larger engine, hence a higher power/weight ratio. Don't get attached to it. When its done, there won't be much left of the original.

The first step is to strip the mower down to the frame. Modern mowers usually have a single stamped piece of steel. Older mowers like this one have frames made of square tubing or slabs of steel. This will give you an idea of how much of the mower is actually usable and how you can lay out the drive, steering, and brake components. Besides the hood, what's leftover to use isn't much. The rest are worthless such as the stock wheels, steering wheel, and transmission.

Step 1: Configuring the build.

The next step is probably one of the more difficult parts of the build: configuration and finding parts. Building one of these is sort of like building a small car with all its various systems. Since all of these racing mowers are one-off type builds, finding the parts that will work can be a pain. I've had a lot of questions about where the tires, clutch, and right angle gear box ( transmission) comes from. the gear box can be found on ebay. The tires are go cart tires and can be found online on any site that sells go cart parts. The same is true for the brakes and rear axle components. The front axle is a custom unit built by a company called Acme Mowersports.

A list of parts needed for this build are:

A: Engine
B: Transmission ( right angle gearbox)
C: Centrifugal clutch
D: sprockets
E: Front axle and spindles
F: Rear axle and axle hangers
G: steering wheel
H: Brake system
I: chain
J: electrical components
K: Wheels, tires, and hubs
M: Gas lever
N: high endurance engine components

Many of the others need to be made by hand. One thing that's helpful is that many of these components such as the rear axle and hangers,wheels, hubs, spindles, and brakes are basically go-cart components. Some golf cart and motorbike components work as well. Sprockets and such can be had from sites such as Mcmaster -carr.

Once you get all the parts, the build actually goes pretty quickly.

Comments

[HammE]

Wow! Just gave me another thing to think about building!

[Huntmaster98]

What kind of clutch did you get and where did you get it?

[brendangillespie]

When you upgraded the stock starter to a high torque model, how did you determine which one to buy? I have a Tecumseh 36680 starter that needs to be replaced and am wondering if I should upgrade it to a better version. Here is the stock:

http://www.amazon.com/Starter-Tecumseh-36680-33605-35763A/dp/B002T4I3RW

[florman]

Hey I want to make a racing mower and was wondering if you could take look at this mower i found for sale near me and tell me if you think it would be a good choice as a racing mower

thanks

Its a Wizard dont know the year

[SimonK95]

We are currently working on a 14.5hp engine, and we have fully stripped down the body and lightened it all, But we don't know hope we change the gearing on it? Any advice would be great, but make it sound simple, as this is our first build? Engine is an Intek so advice would be great?

[Wesley666]

Current racing mower. It does not meet any of the American Racing Mower Associations rules and regulations, for any class because its a high power, 2 stroke from a snowmobile, as well, there is only one class I believe that allows the CVT clutch and transmission it has to be legal. Mostly wanted to make it for the hell of it, see how fast I can get this thing to go (I want it to for sure hit 120km/h, but that is really quite easy for the engine I am using).

Also, bought a different engine then I intended to use. I planned on using an 110hp Arctic Cat engine, but I am selling it and using this little 30hp 340 instead, seemed a little more reasonable. I want to lower this mower in the back, use wheels only slightly larger then the front instead of the big ones that came on it (Also because I am custom making the whole drivetrain, I can make it to whatever wheel size I want) and I want to keep all the body panels on, but adjust the main one so the seat sits lower.

The drivetrain that came off this has both a high speed 90 degree gear box which would be great for a lawnmower engine to get it driving a shaft horizontally, as well as a 4 speed w/ reverse transmission with differential. The transmission is bullet proof, solid cast iron construction. 1st gear has loads of power, if you punched the pedal you could get the front end of the tractor to come way up off the ground, 4th gear without mods would run this tractor up to about 50km/h. I would like to use the transmission in a go kart sometime with a manual clutch, I could make a mean racing machine with that setup.

Old lawn tractors are by far the best lawn tractors you can get, do a pulley swap and tune the engine, you could probably hand a lot of people their mowers on a silver platter with a near stock machine.

[billybob6]

whats the eaisiest way to reinforce the frame because i cant weld

[gschmidt-2]

also, the best way to learn to weld is to practice on scrap metal. under the mower don't have to look pretty as long as it holds. just remember, DON'T weld it all the way, stitch weld it so you don't warp the frame. i live in N.E. and we build mowers that can go 100 mph+

[OleNavy]

Sorry Pal, ain't no mower gone 100 mph yet.

[the doctor who]

(removed by author or community request)

[OleNavy]

And your comment is backed by what????

[grampamurdoc]

http://video.google.com/videoplay?docid=-668943712906921468#

[OleNavy]

I see nothing to indicate this "mower" reached 100 MPH and sustained that speed. Bobby Cleveland driver and racer, sponsored by and employed by Gold Eagle went to the Bonneville Salt Flats (twice) and still was unable to reach 100, but he was close. The video can be seen on the USLMRA website. My brother, Chuck Miller, was there as part of his pit crew for the attempt. Bobby's speed was documented by the Salt Flat organization. So a claim is only a claim unless you have bonafide documentation to back it up. Video of a machine running illegally on a public road doesn't cover it.

[Wesley666]

I just realized though, you probably have to use a stock engine that has been upgraded, not transplanting a monster of an engine into them, correct?

[Wesley666]

No one has gotten a lawnmower to do 160km/h? Seriously? I just picked up a 110hp sled engine from a 2004 Arctic Cat Sno Pro and was planning on putting it in a lawnmower to motor around on. If you can get a sports bike to hit 200km/h with less then that I think I can get a lawnmower to do 160km/h. Clearly, no one has really put in a good effort to get a lawnmower to go balls out. I think I could get a lawnmower up to 200km/h easy with 110hp.

[gschmidt-2]

i have found the best way to reinforce the frame is to use 3/4 square stock along the top corner of the frame. this will make the frame very strong but not add to much weight

[BidEquation78]

i have looked all over for a ragb and can only find either reducers or 1:1 ratio boxs, but most are only rated for 2hp and at a costly $250. could you please give me the specs on your ragb and where you got it.

[westonedelbrock]

go on ec distributing. go on mower parts and the very right bottom link will say right angle gear box. or get a peerless 1100

[westonedelbrock]

go on heymow.comgo on peerless.com. find a p-91

[gregthemechanic]

i was wondering if i take the pulley from the back and connect it to the engine and the pulley on the engine to the back would it make it go faster

[aswracer]

i have a old mtd with 6 speed stock i wanted to know how to make it work for speed?

[westonedelbrock]

go on hey mow.com. otherwise just take out the factory grease and reverse chain and add some realy good grease of gear lube

[rabrantes]

Also where did you locate your fuel tank and how big is it?

[rabrantes]

I really like the design of the frame you built and I am interested in building one during this winter. Could you tell me a couple basic measurements of the frame? How long and wide it is? How far from the front of the frame to where it becomes two frail rails? And the distance from the bottom of the bottom frame rail to the top of the top frail rail by the rear axle. I would appreciate it, thanks!

[McClellan41]

i was goin to do this to mine but never did and now wish i had!!! but might have to down the road!!

[McClellan41]

i have the same thing but not spring loaded its stationary and it has worked out great so far!!

[McClellan41]

so which ratio has a better acceleration (power) 6:1 or 2:1??

[McClellan41]

ya hi i was wonderin what size sprocket i should use on the input to the ragb..i have 17t on my clutch and the ragb is a 1:1 ratio???

thanks

[chivesg5]

I am using a ragb and balts what size poles should I use how fast would it go and from the ragb to the axle iam doing by chane what size sprocte shoul i use

[mowerracer]

I'm not sure what you mean by Poles. As far as speed, it depends on your ratios. On mine , the clutch has a 14 tooth sprocket. From there it goes to a 14 tooth sprocket on the RAGB input. My RAGB is a 2:1, meaning 2 turns in, 1 turn out. The output on my RAGB is a 12 tooth sprocket and from there it goes to a 40 tooth rear axle sprocket which gives me around 35-40MPH on avg. Making the sprockets bigger or smaller will affect the speed. For example, putting a smaller rear sprocket on the axle, like a 35 tooth sprocket would increase the speed. Its hard to determine exactly what the speed will be. Most of us just make a rough approximation then fine-tune by adjusting. I already went to a smaller rear sprocket to slightly increase my speed. Just be aware that most sanctioned racing organizations have a limit on what the final ratio is. I believe 8:1 is typical, but double check with the USLMRA, or ARMA organizations first.

[Ken Chevy]

  Engine/clutch 14tooth -> 14tooth on RAGB=Same ratio.
  RAGB has 2:1 ratio. Now engine turns twice for axle turning once. RAGB has a 12tooth and rear axle has a 40tooth.
   40tooth / 12tooth = 3.33 ratio x 2 (from 2:1 ratio in RAGB) = 6.66:1 over all ratio.  
  Tires are 11 inches in diameter.
  With that ratio your speed will be:
5000RPM=24.56MPH and
6000RPM=29.48MPH.
  Changing ANY of the numbers changes the MPH. If you change to a 36tooth rear sprocket then the ratio becomes 36/12=3:1x2(RAGB)=6:1 total.
Then the speeds become:
5000RPM=27.27MPH and
6000RPM=32.72RPM.
  These are TRUE numbers, IF the clutch is locked up and not slipping. Using belts, there may be belt slippage, making your speed a little slower.
  With a 40/12 ratio, changing rear tire from 11 inch to 12 inch diameter changes speed at 6000 from 29.48MPH to 32.16MPH.
  It would be easy to put all of that into a spreadsheet to show speeds for every 1000RPM and what happens when changing sprocket ratios or tire sizes.
 I made a formula over 35 years ago to figure numbers like that out, the formula is:
RPM÷RearRatio÷TransRatio×TireDiameter÷336.13524=MPH

Nice Instructable.

  Ken Chevy
080810 1316

[gschmidt-2]

OK, after looking at your build i see that you are using a chain instead of a belt. also you are using a cintrifical clutch. whats the deal??? the way we race is with a belt, double pulley clutch. the only chain we use is between the trans and rear axle. i was wondering what rules you are using?

[mowerracer]

I built this mower under ARMA rules for the Pro-X class which means I can use a single cylinder engine and am not limited to using a geared transmission. As such I chose a right angle gear box and a centrifugal clutch because its a much simpler setup. I always found gearboxes to be a pain as there's more to go wrong.

[gschmidt-2]

OK, that makes sense. we only have one guy with an f/x mower. what state are you in? I'm stuck in N.E. and if your not a farmer or rancher there's nothing to do during the summer but race. right now I'm finishing up a mower that i hope will go 100mph.

[mowerracer]

100MPH is probably not going to happen honestly. We have quite a few machines on our team that are running modified Briggs V-twins and even for them we're talking maybe 40MPH tops. During our races our average speed is usually around 30MPH. Trust me- that is going to feel very fast on a rough track without suspension!

Either way, good luck with your build.

[OleNavy]

You should check out Bobby Clevelands last run at the Bonneville Salt Flats. He didn't hit 100 MPH, which was the goal, but he got awfully close to it. He said it was a scary ride. The was a video on the USLMRA website. Bobby works for Gold Eagle and takes their truck to a lot of the USLMRA sanctioned races including the national championship race at Delaware, Ohio, sponsored in part by my brother, Chuck Miller. Chuck owns Miller Lawn & Power in Marion, Ohio and the USLMRA Hall of Fame is currently located in his showroom on East Center Street.

[JOHNTHEREDNECK]

would this ratio apply to mine im running 4500 rpm with8to1 i dont know the tranny ratio yet

[Ken Chevy]

You say you have a box that is 8 to 1.   It has two shafts coming out of it. 

If you hook the engine driveshaft up to one of the shafts, the other shaft will either turn 8 times faster or 8 times slower than the engine is turning.

You will probably be using it to gear the engine speed DOWN, so divide the RPM number by the larger number, that will tell you how fast the output shaft will be turning then.

Input RPM = 4,500 / 8 = 562.5  RPM output speed.

Ken

122810 2127

[JOHNTHEREDNECK]

sorry i wasnt really clear ive got pulleys that are 8 to 1 then they go into the transmission which is either going to be a 5 spd spicer or a 6 spd peerless from a poulan . im hoping on getting 45 to 55 out of it.

[Ken Chevy]

I can't read minds (yet - LOL) and can't see the parts you have in front of you.

So, you have to give me numbers.

Make a mark on the input shaft of the transmission and another mark on the output shaft.  Then put the transmission in 1st gear and count how many times the input shaft goes around to the output shafts ONE time.  If the 5 speed goes around 10 times to one time for the output shaft in 1st gear, then that is 10/1, and 7 times in 2nd gear it would be 7/1 etc.

You HAVE to have the numbers to figure out the ratios.

So you will HAVE to get both transmissions, mark the shafts and count the turns to get the ratio for each gear...OR that info (transmission ratios) may be available from a dealer. 

But you MUST have:

Engine RPM
Pulley ratios
Transmission ratios
Rearend ratio
and, last but not least the Tire Diameter.

Once you have those numbers, then input them into the formula I furnished:

EngineRPM÷RearRatio÷TransRatio×TireDiameter÷336.13524=MPH

If, for example, you have 4,500 Engine RPM/8=562.5 engine RPM
562.5/6
Rearend ratio of 6/1
Transmission ratio of 5/1
and a Tire Diameter of 12 inches

then we would do 4500/8=562.5
562.5/6=93.75
93.75/5=18.75
18.75*12=225
225/336.13524=.6694 MPH

Less than ONE MPH @ 4,500 RPM engine speed.

So, get rid of the 8/1 and make them 1/1 pulleys.
Then the MPH would be 5.355 MPH

Change the rearend ratio from 6/1 to 2/1 and then you have 16.065 MPH @ 4,500 RPM engine speed.

Then change the transmission ratio to 1.5/1 and your MPH would be:

53.5499 MPH @ 4,500 RPM's of engine speed with a 12 inch tire.

4,500 RPM engine speed (w/1/1 pulleys) + rearend ratio of 2/1 and transmission ratio of 1.5/1 with a 12 inch tire = 53 MPH

Put different numbers into the formula, John.  It will work every time.  It is simple, 2+2=4 every time.


EngineRPM÷RearRatio÷TransRatio×TireDiameter÷336.13524=MPH

I used to use that formula a lot when I was drag racing years ago. 

You can use a regular calculator, use the one in your computer works fine, and just do them one step at a time.    Try it, figure out some ratios, John.

And, like mowerracer said, 45 to 55 MPH is pretty improbable without having an engine putting out a LOT of horsepower!

And it would take so long to get up to speed too, because of lack of HP.

You might try it with a 3.5 rear ratio to start with and that will be about 30 MPH and see what that is like.

Ken

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