# Race Mower Project



## Billh51

My Grandson Drew and I have started a project in the shop, building a race mower. There’s a small local group that have been racing for about three years and the machines are getting a little more advanced as time goes on. I built my Grand daughter  Vanessa one last year and she has done very well with it. Now it’s time to update my Grandsons machine to keep up with the rest of them.

We are starting from scratch with a bare frame and will build and machine all parts in my shop, as I had done with the previous machine. Drew is a junior in high school and takes all the shop classes available, so we are having a great time building this together. He is a very quick learner and is catching on to the lathe and milling machine, rather quickly. I am certainly no expert but I am trying to teach him the proper way do do things, while keeping shop safety at the top of the list.

I should have been taking more pictures but I have a few to start with. I may post a few more down the road as the project progresses. I will include a few pictures of the one I built last year. My Grand daughter Vanessa did help build her machine but not to the extent of machining the parts.


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## Cadillac

I like the heim end configuration on the front end. I wish we had that around our area looks like lots of fun. Good job!


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## eugene13

Looks like the beginnings of a real race mower, keep the pics coming.


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## kd4gij




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## Billh51

kd4gij said:


>



I had forgot about that’s episode, funny stuff.


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## Billh51

We made a little more progress on the race mower over the weekend. Got the wheel studs pressed into the hubs and started machining the rear axle. We were able to mock up the rear axle to help set up the Ackerman for the front axle. One small step at a time.


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## Joe in Oz

Thanks for letting us watch your progress!
A question: most cars have the "king pins" or steering knuckles close to or on the centre line of the hub. Gokarts and your race mower have the whole steering mechanism on the insed of the wheels - even some distance away from the wheels. I don't understand why. That would increase the forces on those pivots enormously and make the Ackerman steering geometry seriously ineffective, as the wheels go around an arc, rather than pivot around their centre line as Ackerman would have anticipated. Is it a fabrication issue or a racing geometry reason?
Cheers,
Joe


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## Billh51

Thanks for your reply Joe. I'm kind of new to this myself but after doing a lot of research on race mowers, this is how they do it. I understand what you mean, thinking it may just bind up but it seems to work. My Grand daughter won both her heat races and the feature, first time out last year. The mower handled like a dream, very smooth in the corners. She lapped all but the second place mower. This one is built very similar but with more adjustability in the front end.

 These mowers are very rigid, ideally no flex in the frame. When you turn left, it hikes up the left rear tire and lowers the right front. This helps turn the mower and puts all the bite on the right rear. You can drive it pretty deep into the corner. At least it all sounds good on paper, right? Lol


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## FOMOGO

Great job on your grand daughters ride. Are there any rules regarding engine use and modification? Cheers, Mike


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## Tozguy

Are you allowed to tweak the cutting blade for better ground effects in the straights?


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## Billh51

FOMOGO said:


> Great job on your grand daughters ride. Are there any rules regarding engine use and modification? Cheers, Mike


Hello Mike,
 When this first started out 3 years ago, it was petty much run what you brung and hope it ran till the end of the race. Now things are progressing a little more and we are trying to go by the rules set forth by some of the racing organizations. The models we are building would be in the FX class. My Grand Daughters is a single cylinder 16 HP and my Grandsons will be an opposed twin cylinder 20HP. Surprisingly, they should compete with each other quit well.


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## Joe in Oz

Thanks Bill. I wonder if there is anyone here with automotive engineering background who can shine some light on the issue?
I'm sure there are good reasons why it may not make a difference to light weight vehicles where exactly the steeing axis is.
I look forward to your continuing efforts and your grandkids' successes!
My grandkids are only 9 and 11 - but both can ride motorcycles (REALLY well) and dirve our little "paddock bomb" Subaru Brumby/Brat.
They are starting to get interested in Motor Trials riding - I support that, because the skills are always helpful and the risks are pretty low compared to any other motor sport.....
The local car club has an off-road facility and can issue juniour racing licenses for "no speed" events to 12 year olds. So I have the Chirstmas present sorted for the then 12 year old 
Cheers,
Joe


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## Billh51

We haven’t had much time lately to work on the race mower, my Grandsons a busy guy. However, we did get together last night for dinner and we’re able to spend a couple of hours in the shop on our project. We drilled out the other hub for the lug bolts and then pressed them in. Forgot to snap a few pictures, having to much fun. Then we pulled the shaft back out of the machine to mill in the key ways, now that we know where everything is going be.


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## TerryH

Very cool project!


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## matthewsx

Let me know if there’s anything you need. I have a ton of race kart parts from my previous business. I also have some custom Kawasaki engines, a couple of transmissions and a scatter shield for a Briggs horizontal flathead I bought when we were thinking of building a race mower. PM me for details. 

Thanks,

John


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## Billh51

Thanks John, we'll see what comes up as we progress on the mower.


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## GoceKU

Interesting project, and you've done some beautiful machining on the rear axle, my question is, why are using the OEM tractor sheet metal frame, aren't you better off making an tube frame and integrating a bit of flex and a roll cage for safety in any motorsport, bending the rules is half the winning, can you explain the surface and the rules of this racing series. Nothing like that around here.


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## Billh51

Thanks for your reply. The whole idea is to keep it cheap and simple, so everyone can compete on a fairly level playing field. Some people have the skills and the shop to build in, such as myself but others are not so fortunate. The whole idea was to give the kids something constructive to do in their spare time, learning building skills and also having fun racing, while lot of the Mom and Dads show up to watch.
 After building my Grand daughters racer last year, I guess I kind of upped the game a bit, because she was so successful. I have been helping the other kids with their mowers also, trying to get several of them in this faster class of racer. We will probably have two classes of mowers this year as some of the others can’t run with this mower.
 They are holding the races on a red clay hay field, nothing fancy but a lot of fun. It’s an oval track with about 175’ straightaways, so it isn’t very big but makes for some good close racing.
It would be a lot of fun to just design a tube frame with suspension and all the good stuff but I believe you would wind up racing yourself, as there isn’t any of that type around here.


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## GoceKU

Billh51 said:


> but I believe you would wind up racing yourself, as there isn’t any of that type around here.



I know exactly what you mean, i've done it in few times myself but some times is good, makes others get more involved and makes the racing that more cooperative, i can remember betting cars with twice my horsepower on street tires week after week because i was able to figure out how to make my own 4 link rear suspension with a welded diff that transfers the load perfectly and can apply all the power without any wheel spin, so steer your grand children into doing more research and looking 5 steps ahead.


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## Billh51

We were able to get a couple more hours on the race mower over the weekend. Got the motor mounted up into position so we could get the steering system set up. We were able to lay out the front and rear mounts for the steering shaft and built and installed them. Another small step.


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## Billh51

We had a chance to work on the project for a while today and got a few more things done. We have been trying to concentrate on the steering components and we were able to design and build a few more pieces. I know it doesn’t look like a lot was done but it all takes time and we’re sure having fun doing it. The drive system is up next.


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## Billh51

Well I have a little update on the race mower project. I had to put it on hold for the last several weeks do to a home remodeling project that took precedence over the mower. I gutted our master bathroom and did a complete makeover, something my Wife has wanted for a while. Anyway it’s all done and I get to play in my shop again.
 We did get a chance to get several things done on the racer and I think it’s coming along quite well. We concentrated on the drive system and have that pretty well completed. I am waiting for the sprocket for the rear axle so we can compete the chain drive to the gear box. The clutch system is in and should work fine. I didn’t bother with all the keys for the shafts at this time because it all has to come apart again for painting.
 The steering system is pretty well completed except for a steering wheel, which we need to find yet. All the fasteners on the steering system will have nylock fasteners when it is reassembled after painting. As the last picture shows, we are setting up the rear fenders and seat assembly, using a cad program, lol.
 All the figuring and hard work is starting to show some results now. Hopefully we may have it wrapped up in a few weeks.


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## GoceKU

Great progress Bill, i really like seeing stuff like this. Is there something in the rules against running front suspension, with the steering support there it will be very easy to mount shocks and if you get the spring rates right you'll have very big advantage in the corners.


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## Billh51

Thank you for the reply. The rules that we are running under don’t allow for front or rear suspension. I agree that it would be a huge advantage in the corners but the idea is to keep it rather simple in design, so more can compete.


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## GoceKU

Bill, you know there is a way to cheat, you can use a truck leaf spring in the middle of the front axle and you'll get limited suspension travel that can make all the difference.


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## Billh51

We made a little more progress on the racer today, getting the rear fenders fabricated and a seat back welded in. It was another great day in the shop with my Grandson.


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## PHPaul

Dang, that looks like it's gonna be a fun machine!

What sort of speeds do they attain?


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## Billh51

The machine is geared to hit a top speed of about 28mph. This can easily be changed with sprockets to make adjustments if needed. The way it is set up seems to work well for the track they are running on, utilizing the torque band of the motor.


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## Superburban

Joe in Oz said:


> A question: most cars have the "king pins" or steering knuckles close to or on the centre line of the hub. Gokarts and your race mower have the whole steering mechanism on the insed of the wheels - even some distance away from the wheels. I don't understand why. That would increase the forces on those pivots enormously and make the Ackerman steering geometry seriously ineffective, as the wheels go around an arc, rather than pivot around their centre line as Ackerman would have anticipated. Is it a fabrication issue or a racing geometry reason?
> Cheers,
> Joe


Having the king pin closer to the center of the wheel, is always better, but how much? In this case, there is no way to fit the kingpin inside the rim. The next best solution, is to have the line drawn through the kingpin, to meet the road in the center of the tire contact. 

So what happens if the line is not in the center? A blowout, can cause the steering to pull dramatically to that side. An issue with the braking, can cause the steering to pull, as can bumps.  In this case, with the small tires, and no brakes on the front, None of those are going to show much, except maybe the bumps. A big bonus of having that line meet to the inside of the wheel center, is while moving, the forces are trying to pull both wheels outward, Essentially taking any play (what we call backlash) out of the steering system.

In the end, it is all trial and error. Just look how race car teams spend the week prior to a race getting the car dialed in to that track.

You can not just angle the kingpin more, as the steeper the angle then you are causing the front end to lift when the wheels are turned. But that does add a benefit of the weight helping to keep the steering centered.


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## Superburban

Billh51 said:


> We made a little more progress on the racer today, getting the rear fenders fabricated and a seat back welded in. It was another great day in the shop with my Grandson.


Can I be your grandson? 

Great work, something your kids, and Grand kids will remember forever.


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## Tozguy

Bill, thanks for bringing us along 'for the ride'. I am enjoying your project tremendously.
How important is tire choice and are there many different tires to choose from?


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## john.k

My old rider mower has a rigidly mounted front axle like that,and it s always getting stuck when a drive tire lifts ...........I was gonna pivot the front,but someone here suggested a truck spring leaf as the centre part of the axle,and that is still rigid mount ,no complication with the steering.(Its centre pivot tiller)


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## matthewsx

GoceKU said:


> Bill, you know there is a way to cheat, you can use a truck leaf spring in the middle of the front axle and you'll get limited suspension travel that can make all the difference.


I built racing kart motors for several years as a business. Whenever someone came to me and wanted a cheater motor for their kid I would ask them how it would feel if their kid took first place and then got disqualified for cheating. 

Bill has the right idea here, build it strong and help your competitors to do the same. I guarantee his grandkids will have way more fun coming in third in a big field than running away in first place with nobody even close. Racing should build skills AND character  

John


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## Billh51

Tozguy said:


> Bill, thanks for bringing us along 'for the ride'. I am enjoying your project tremendously.
> How important is tire choice and are there many different tires to choose from?


I’m sure tire choice would be important if you were running in some of the bigger tracks at organized events. However, these kids are just running a track in the middle of a hay field, so most are just running stock mower tires . Thanks for following.


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## Billh51

john.k said:


> My old rider mower has a rigidly mounted front axle like that,and it s always getting stuck when a drive tire lifts ...........I was gonna pivot the front,but someone here suggested a truck spring leaf as the centre part of the axle,and that is still rigid mount ,no complication with the steering.(Its centre pivot tiller)


We did a lot of research before starting the build, especially on the front end. The trend seems to be a stiff frame, with no flex. A solid front fixed axle that does not pivot and preferably a solid rear axle. With the kings pins angled back at 10*, when you turn left, this causes the left rear tire to lift. This is what makes the racer turn, without pushing in the corners. This arrangement seems to work on my Grand daughters racer we built last year as it handles quite well. The tire pressure will also have an effect on the handling.


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## Billh51

matthewsx said:


> I built racing kart motors for several years as a business. Whenever someone came to me and wanted a cheater motor for their kid I would ask them how it would feel if their kid took first place and then got disqualified for cheating.
> 
> Bill has the right idea here, build it strong and help your competitors to do the same. I guarantee his grandkids will have way more fun coming in third in a big field than running away in first place with nobody even close. Racing should build skills AND character
> 
> John


I couldn’t agree more John. That’s the whole idea is for the kids to be doing something constructive and having fun, while perhaps learning a few skills. I tremendously enjoy that shop time with my grandkids, something that doesn’t last forever, so take full advantage of it while you can. It is also a pleasure to help out the other kids with their machines and watching them race as well.


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## tweinke

Awesome build! Even more so because the kids are involved!


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## pontiac428

So how much is this grass cutter going to weigh, all up?


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## Billh51

pontiac428 said:


> So how much is this grass cutter going to weigh, all up?


I am not to sure what it might weigh. I would assume it might be close to the original weight or less because there is no mower deck anymore. Also the original transmission outweighs the new drive assembly.


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## Billh51

We made some more progress on the race mower, getting a little closer all the time. We fabricated the hood and cowling assembly from some old sheets of aluminum I had been saving from a scrapped aluminum boat. They were from the seats so it was reasonably flat to start with. Along with that we built the front and rear bumpers and welded them in place. Probably going to build the seat next and then get it wired up. Not too far from disassembly and paint.


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## Billh51

We finally finished up the construction part of the race mower build. We found a steering wheel and built a hub to get it mounted to the shaft assembly. Made a mount for the battery and wired up the chassis and tested it out. Everything works as it should, thankfully. We tore it all apart today and prepped it for painting, getting everything done that needed a primer coat. If the weather cooperates tomorrow, we should get some of the colors on. Not too far from trying it out.


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## dave_r_1

No test run before painting?


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## Billh51

dave_r_1 said:


> No test run before painting?


It was tempting to try it out but there are a few things to be done yet. No throttle control and the slack chain sprocket is still on back order, should be next week. It was a thought though.


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## dave_r_1

I've just found that, for my projects where I fab up something that's mostly new, that it takes a couple of rounds of modifications to get it working well,


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## Billh51

dave_r_1 said:


> I've just found that, for my projects where I fab up something that's mostly new, that it takes a couple of rounds of modifications to get it working well,


I think that’s true for most of us Dave. I’m sure we will be playing around with the castor and camber along with tire pressure to get it to corner well. We have kind of a baseline figured out and will adjust from there. Also could be some sprocket changes to take full advantage of the torque band on the motor. Hopefully we don’t have any major chassis changes to make. We are looking forward to putting it all back together.


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## Billh51

The weather cooperated for us and we were able to paint the colors on the mower over the last two days. Assembly is up next. We’re excited.


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## Billh51

Well we finally got back on our project after a little delay, had to go out of town for a bit. We finished all the painting and started and finished the assembly of the racer. Everything went well, we took our time making sure everything was dialed in as best we could. Hopefully eliminating any problems down the road. The motor runs great and the mower seems to handle quite well. The real test will be to get it on the track and make all the final adjustments to the front end and tire pressures. 
 We sure had a great time building it and I know my Grandson learned some new skills he can use in his shop class this year when school starts. Nothing like a project with the kids. Also, thank all of you that followed this project through and all the kind and interesting comments.


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## Boswell

Billh51 said:


> We sure had a great time building it



That is so awesome. What a great project to teach the fundamentals of design and fabrication.


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## tweinke

Be sure to let us know how it all works out once on the track.


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