Step 2: Frame reinforcement

The next step is to beef up the frame or make alterations that will work with your components.Its important to realize that these mowers will be racing on what tends to be really rough dirt track. They have no suspension, thus the frame takes a severe beating. Reinforcement is critical to avoid having the frame flex and ultimately crack from fatigue. The rear of the frame was cut about 6" from the rear. Throughout the build, I used 1x1 square tubing which is easy to weld and work with. This is what I used to create the square frames in which the mounting brackets were welded into to hold the rear axle bearings. I chose to use a 1/1/4" rear axle because that size is highly common and thus easier to get parts like wheels and sprockets for.

These square frames were welded into the frame, then the end I cut off was welded to the back. The minimum height requirements for my class is 4" from the frame to the ground. So its important to know what size wheels you plan to use and where to mount the axles in order to meet that requirement. The lower you can go, the better handling the mower will be. Mine site just at 4" off the ground.

Next, I welded two lengths of square tubing along the top of the axle brackets to the front tubular frame. I did this because the transmission will go underneath. A piece of diamond plate will cover it, and above will be the seat. This will give me easy access to servicing the chain and transmission and also protect me from flying debris or potential chain failures.

I am using a right angle gearbox for this build. Why? Because the other choice is to use a 3-5 speed gearbox used as standard equipment on mowers. These work fine, but it also means you'll have to change the grease in them and perhaps invest in hardened gears since the originals will strip out much easier. With a right angle gear box, or RAGB, there's only two moving parts. Plus, they are made for higher speed applications and therefor perfectly suited for this application. More simplicity means more reliability.

Additionally, I am using a centrifugal clutch. This is a higher quality, higher HP rated unit that is heavier duty than typical go-cart clutches. The springs can be adjusted for higher or lower engagement.
<p>I have a sears lawn tractor iI use to cut grass on a hill. the parts for the brakes are no longer available. I want to add brakes to the mower, perhaps on the front wheels. The current transaxle is a Dana 6800-1 and it has a shaft sticking out of the side of the transaxle that has a crummy disk brake system on it. Any ideas how I can beef up the brake? I don't want to race but I would like to be able to stop.</p>
<p>take it apart and sand stuff to create more friction</p>
<p>i have a old mtd with 6 speed stock i wanted to know how to make it work for speed?</p>
<p>if you want free speed then what i did with mine is i kept stock,transimission,frame,tires,etc. but i robbed a pulley from the mower deck and cut it up to fit with my moon key. the alternative is welding a smaller pulley in the back, i hope i answered your wuestion but if thats not what you meant then pressureize the transmission oil</p>
really great Instructable and comments. Few things I'd add, anybody try sprint car gas? my father used to tractor pull with multiple big block engines and he used 125 octane gas(seriously it durometered as that) the performance jump from that in small engines(from Briggs to dirt bikes) was incredible. the engine has to be built for it (bottom end) so crank, rods, billet flywheel, etc, as in the Instructable but it's almost like a supercharger in terms of extra HP. another thing would like to agree with porting comment. I'd natural aspirated(carb or injection) you want the intake slightly rough to mix air fuel, exhaust as smooth and unobstructed as you can. we used die grinder with carbide cutter tip (cross section screw looking oval shape) same as big blocks. took flathead brigs &quot;L heads&quot; and made &quot;y heads&quot; hah! also ground the cams on them (decreased duration by grinding g lobes thinner and increased lift by welding a bead on the top of the lobe and grinding down. seems we advanced the timing a bit too from the crank. with higher octane it tends to run drier so you have to fatten up the fuel mixture. again great Instructable thanks, very detailed and thorough. btw anybody use comet differentials or clutches? seems differential might give you better handling, also since it's circle track, do you stagger wheel size left to right like sprints do? seems some of the camber and steering issues might be addressed with that.
yeah, unless you use a turbo (or smog air pump I.e. &quot;poor man's&quot; supercharger), definitely want the intake turbulence, especially if you run methanol) not sure for high rpm If a tunnel ram style intake might work? never tried that but who knows. seems a dyno would be a great thing for these engines to really tune them. we had a 3hp Briggs on a minibike in high school that with centripetal clutch and no trans would do almost 40. had a Harley carb AND burned 60/40 125 gas / ethanol mix though, HAH! crazy days.
Hi i have a 23hp red snapper and i wanted to use it to get the mail and dump garbage. What would i have to do to it? Thanks
I have a 2006. Huskee 18.5 briggs and stratton and wanting to place a racing air filter on itinstead of having the reglar one on it how would i go about.
I have never build a racing lawn mower this is my first attempt, I have spent the last two days and approximately $50 building my lawn mower. I have a MTD, with a 17.5 horsepower motor I put a 2.5 inch pulley and the rear and a 7.5 inch pully up front. I had a friend of mine up the RPM's by 450. I lowered the rear 3 inches and the front 2 inches. this is a 6 speed on the go by the way. I am running 20x8x8, tires in ther rear my 2 questions I have do they make a 24x8x8 tire and does the muffler really restrict that much? I do have a wheelie bar on it today on the test run I was able to hit 40 miles per hour on GPS. thank you, oh and I have a kill switch lanyard on it as well.
Hello traced1. I am working on building a racing mower would i have to modify the whole mower to catch a little speed. On a 18.5 hp briggs and stratton motor. Mtd huskee
<p>Great job! I had to comment on your connecting rod incident.</p><p>I had something similar happen to a stock 14HP B&amp;S engine on my Snapper. I was mowing right along and all of a sudden the engine just died (no bang or any other dramatic sound). </p><p>I got off my mower and saw this large hole in the engine block and oil everywhere. Upon investigation it appeared that one or both of the nuts that holds the connecting rod to the crankshaft had vibrated loose! Doesn't B&amp;S use Lock-Tite on connecting rod fasteners from the factory? I could not see any trace of Lock-Tite (red/blue/green).</p><p>I ended up buying a used Kohler engine for $150 which was older than the mower and it was still running great until I sold the Snapper about a year ago.</p>
well it is 2015 no one has answered me maybe this will help someone in the future just by reading. If you're looking at buying a lawn more to turning it into a racing one this is what I have done. first off find you A MTD mower or another more that the pulleys are held on by a bolt not pressed on its just a much simpler process however you can get the press on pulley type if you have a pulley puller. I remove the 7.5 pinch pulley from the rear hi then installed a 2.5 inch pulley and the rear then I pulled the front pulley off cut the smaller pulley that is on top but just the upper neck off. the 7-inch that was in the rear I welded it to the front pulley and reinstalled it. yes know once you do this you will have to readjust v clutch linkage actually make it slightly longer. I also adjusted the governor up 450 rpms. I removed the front wheels the small hole in the center that allows it to pivot I cut it off clean reinstalled drill new bolt holes the whole the fun together in the rear I simply cut part of the main frame out to drop it three inches in the rear then 're-forced the metal. I managed to hit 40 miles per hour one time for the most part 33 to 35 miles per hour therefore I am going to take the front pulley off once more weld a 9 inch to the front and see if that will get me a consistent 40 to 42 miles per hour. just remember keep the wheel hub assemblies greased make absolutely sure you lower the lawn mower at high speeds these things are very unstable though it may look stupid I wear a helmet and a jackethopefully this will help someone in the process of them doing their first build. by the way if you build it correctly trust me you will need a wheelie bar.
<p>Few comments for others reading this. First check with the organization u plan on running with to get rules before building. Some don't allow centriinjectclutches and use a gear transmission.</p><p>As far as porting and polishing, my teacher in tech school raced and built engines for motorcycles, snowmobiles and go carts. He taught that polishing the exhaust is fine. The intake side can be sanded after porting, but not polished. A slight roughness on the walls will cause a slight turbulence in the in coming air, which will help the air and fuel mix together (atomize). If smooth, no turbulence and possibly an air fuel mix that's not fully atomized and the fuel could separate from the air. That's why fuel injection works so good.</p><p>Put some grease or cam assembly lube on the valve spring retainer clips to hold them on the valve when assembling. If using the hammer and socket method to disassemble the valve springs, put a rag over top to help stop the retainers from flying and a rag under the valve head will hold the valve from moving and let the spring compress.</p><p>Wasn't talked about here, but always lube the cam lubes and bearings with assembly lube (STP oil treatment works too) when assembling engine. </p><p>Hope this helps some of u out.</p>
Im working on building a race mower and im wondering how the build will cost
<p>Go in a class that runs stock engines. After a year or two u should have the bugs worked out of the mower and be ready for more power.</p>
Depends how crazy you go on it. I spent $1000 build a mower, and that wasn't anything fancy. As well, since I went with fairly cost effective solutions it did not adhere to racing lawnmower specs so it can't actually be raced, however that was never my intention so that was alright.
<p>What kind of welder will work for welding on the frame?</p>
<p>All types will work. If u don't have one and are looking to buy one, I would suggest a 110 volt portable wire feed. I have a Hobart 140 (made by Miller) which can weld with gas (cleaner weld) or flux core wire and weld sheet metal and steel up to 1/4&quot;. If u want a different brand, just get a similar size and type. Also if u buy the flux core wire, spend a little more and buy the better wire from a welding supply shop. Have had problems with wire sticking in tip with cheaper wire.</p>
<p>I have a yard machines shift on the go riding mower that I want to turn into a racing mower. I want to know how fast I will go with an 11hp briggs and Stratton engine, a 8.5 engine pulley, and a 5.5 axle pulley. and I have a video of it on youtube. here is the link </p><p><a href="https://www.youtube.com/watch?v=PRUrSpy69fg" rel="nofollow">https://www.youtube.com/watch?v=PRUrSpy69fg</a></p>
Where did you get your RAGB from? and how much did it set you back?
I got mine from Ebay. I have two of these, one as a spare. The first one was $30. The second was $50. They seem to be getting a bit harder to find. The cheapest are older RAGBs for riding mower decks. They typically have 2 bolts, but that will work fine.
<p>what are your RAGB's off of exactly if you know. or even better how do you find them?. Everyone I fine is over a hundred dollars.</p>
<p>A brilliant build brilliantly explained. Love the stripped down raw appearance, this thing looks like it would absolutely fly! This might be of interest for those following this post <a href="http://lawnmowerwizard.com/featuredarticles/worlds-fastest-lawn-mower/" rel="nofollow">http://lawnmowerwizard.com/featuredarticles/worlds-fastest-lawn-mower/</a> it's frankly ridiculous!</p>
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: <br> <br>http://www.amazon.com/Starter-Tecumseh-36680-33605-35763A/dp/B002T4I3RW
where did u find/get a high torque starter? i have a couple of racing mowers myself. thank u in advanced. :-)
I was wondering what brand of clutch you have or recommend for using and how wide is you're axle
One thing I didnt see you make any mention to. But there was a pict of it modified in one picture was the crank case breather? Do you over size this at all? I know this is done on alot of race cars but wasn't sure if you had done anything with it
<p>where did you buy most of your parts (brake, clutch, ect..)</p>
<p>I have been told you have to watch where you take meat off inside the head when your porting a head. I have heard this can actually make the engine put out less power if not done just so. Is this true ? Do you have to be expert at it , or just know the basic goal ?</p>
You also mentioned you wasn't sure of the gear ratio. To figure the gear ratio you simply take the larger gear which i think you said yours was a 40 an divide the smaller clutch gear 14 thus giving you a 2.86 gear ratio.
If you decide to up your cam to a performane cam check out dyno cams they work great easy to set up an they will be glad to help you with your timing valve springs and differnt spring tensions as all this will play a role with an aftermarket cam. I would also suggest investing in a dagree wheel if your modifing yourself your going to need one. BMI karts is also an excellent kart shop to buy any frame components you may need in the future affordable prices. Turk bros. For any of your engine parts. I have built many karts an racing engines over the years an these places work well for service an price. I wish you the best hope this may help out. Feel free to email me with any engine questions b glad to help.<br>
<p>how did you connect the engine to the gear box, do you have pics on that</p>
<p>if you put a 9 inch pulley on the front and a 3 inch on the back you would have to custom your belt but how fast would that ratio go 9:3</p>
<p>I wan to make a electric car for mech project I need a dc motor less than equal to 3000 w max rpm 3600 max torque 12.8nm at 2400 rpm power consumption max 48 volt can u recomend me some motor name or link which would suit best for me....thanx in advance...</p>
<p>I am not sure which is more impressive; your project or your very excellent narrative. My compliments on both efforts.....</p>
My uncle has a 340cc 4 stroke and my dad has a 370cc 2 stroke which one<br>Should I use and I am using one of these engines<br>For racing can I have some<br>Advice.
What kind of engine and what size did you use<br>For your mowers
Depends if you actually want to race it in mower racing competitions or just use it as a hooligan tool. Racing there are very specific rules you have to follow to be able to compete, and you would have to research these as there are several race types based on modifications, engine displacement, etc. If you are using it as a hooligan tool, you can do whatever you want. I used a 340cc twin 2 stroke from an older snowmobile running around 40hp which worked quite well. Using a non-stock engine to your tractor is more difficult though because you need to modify the drivetrain. I had to completely machine a new system for mine, brackets welded on for bearing supports, shafts machined, sprockets, chains. Real pain in the ass was odd sized shaft needed for the secondary clutch. The stock engine is best to go with in my opinion.
How many mowers do<br>You guys have?
Hay I'm a ten year old <br>Kid and I always wanted <br>A Lawn tractor do any<br>Of you guys/girls now<br>Anybody in Nova Scotia<br>With a lawn tractor for sale<br>Let me know Thanks
how to fast does it run?
This is a great Instructable, but you need to add a main image for the project!<br /> <br /> Please do that, and reply to this comment so I know when you are done.<br /> <br /> Thanks!
Wow! Just gave me another thing to think about building!
What kind of clutch did you get and where did you get it?
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 <br> <br>thanks <br> <br>Its a Wizard dont know the year
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?
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). <br> <br>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. <br> <br>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. <br> <br>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.
whats the eaisiest way to reinforce the frame because i cant weld
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+

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