Maniac0301 HalfDork
6/19/20 12:09 p.m.

Inspired by the GRM reposting of the converting lawn machinery into hooning enablers I started looking for a lawn mower to convert into a go kart for the kiddos.   I ran across an ad for a pair of John Deer rear engine mowers for $60.   I immediately jumped on the deal and picked them up during a long lunch at a rallycross event.   It was certainly a trial getting the pair of lawnmowers and my MR2 back home but with the help of some of the other racers we got everything situated.   Here are the future karts as I got them.

The R92 has the recommended peerless diff chain driven off the transmission.   The RX73 has a working 9hp pull start engine.   I plan on mix and matching parts welding where needed until I get something that runs.   First step is breaking them down to get to the good bits and get rid of the silly flying saucer shaped lower ballast.

I've heard the old decks sell for decent money so we'll be cleaning those up maybe giving them a once over in patented JD yellow and posting them for sale.   

After pulling apart the bottom side we started pulling off the top to get to just the juicy middle bits that will make the chassis of the karts.

And repeat for the other kart. 

And now finally down to the good bits of the R92

My plans will be to relocate the axles up into the frame and chop and weld the front steering assembly to also lower it.   I'm looking for a couple inches of ground clearance.  As I weld in the front I will be adding in some camber and castor.   I will be relocating the engine and transmission and I think I'll be using the R92 frame pulling the engine and any other levers or springs or hardware from the RX73 as needed.

I'm not sure yet how I'm going to drive the transmission from the engine nor how I'm going to handle a clutch or brakes.   Still have a bunch of things to work out.    One of the goals of this project is to help the kids start to think about problem solving in engineering.   I will explain what we are trying to remove or accomplish but I want the kids to figure out what needs to be added or removed to get there.   I've hardly turned a wrench on this thing so far and I hope to continue that process throughout most of the build.

Indy "Nub" Guy
Indy "Nub" Guy PowerDork
6/19/20 12:19 p.m.

In reply to Maniac0301 :


If you saw the other thread, then you know I'm in the midst of building one with my boys too.  I'll be following along.  How do you plan to do your steering?  That has been wondering.

Maniac0301 HalfDork
6/19/20 12:34 p.m.

In reply to Indy "Nub" Guy :

I plan on welding a plate to the bottom of the steering shaft that the existing steering rods will bolt to.   I'll get rid of the weird geared and toothed setup and simplify it like most Go Karts.   I'm hoping this doesn't make the steering effort too great for the kids but it does have a pretty large steering wheel to give them some leverage. I expect with the different angles of the steering shaft and the hubs I'll need to cut and weld where the steering rods attach at the wheels to keep it from binding.

Maniac0301 HalfDork
6/28/20 6:28 p.m.

After cleaning up the decks and putting them up for sale we stripped the rest of the R92 chassis.  I settled on this one for the kart.   To get the front where I want it I cut the bar that connects the two front spindles together and rewelded them to the frame.  This let me widen the track and push the front wheels forward.   I also added in a bit of king pin angle and camber.   I'm hoping to strike a balance between performance and making the kart stable and easy to steer.

Maniac0301 HalfDork
7/1/20 10:55 a.m.

We were able to strip the rest of the chassis and the kids got busy cleaning the chassis, grinding off some rust and then painting the cart.   I've also been doing some research and ordered some bits for the the clutch and braking system.   Hopefully what I have in mind ends up working.

Carl Heideman
Carl Heideman
7/1/20 6:29 p.m.

Great project, glad to see the kids are hands-on.

If you want more pictures of how we did ours in the original Yard Kart story, let me know.

Maniac0301 HalfDork
7/2/20 8:48 a.m.

In reply to Carl Heideman :

Thank you very much.   The kids have been very involved.   I tried as much as possible to explain what we needed to do and why but then let them loose on the how.   Discovering or teaching them all the little things that go into working on something like this.

I know I have a very similar platform to yours.   In one of your karts you retain the 5 speed transmission which I'm trying to do as well.  My plan is to run a centrifugal clutch off the crankshaft to a sprocket at the transmission.   We are quickly running out of space for all this.   How did you package the kart that retained the transmission?

Carl Heideman
Carl Heideman
7/3/20 8:05 a.m.

Retaining the 5 speed was a lot of work, but worth it.  The gearbox sits pretty high on the frame, and we couldn't get the seating position right with it in place (I think that may be why Indy Guy lengthened his kart).  So we lowered the gearbox into the frame with some angle iron mounts.  That was pretty easy.  Then there was a lot of packaging work to make the clutch, brake, and other linkages to work.  It took some serious creativity and a jack shaft to make it happen.  We ended up being able to reuse most of the linkage from the original mower with each piece slightly modified.   The kart has a gas pedal on the right (easy modification to the original brake pedal) and the left pedal is a combined clutch/brake--half way down is clutch only, all the way down is both.  Jack really wanted a three-pedal setup, but there wasn't enough foot room to do it without having a pedal stick way out.  

The picture below must be from before we got the combined clutch/brake pedal finished.   I think we had a hand throttle at the time and still had brake on the right, clutch on the left.  The kart went through a lot of iterations.

 The longer rod running along the framerail is the brake, and the diagonal rod is the clutch.  Eventually, the brake rod got connected to the extra hole in the clutch arm and was adjusted so the brake didn't start actuating until the clutch was about half way through its travel.  I don't know if that explanation makes much sense, so I'll get you a picture of the final setup. 


If you use a centrifugal clutch, you could do a very similar setup and not have so much fussing with linkages.  

By the way, the gearboxes are similar to dog-ring boxes internally and can be shifted without clutching.  I recommend clutching as we have seen some breakage from banging the gears too fast.

And also by the way, we made the shifter by modifying a dual-cable snowblower shute control rod.  We spent a lot of time at the lawnmower junkyard staring a various parts whenever we had a problem to solve and sooner or later would figure out something that could be modified to fit.  I'll get you a picture of that too, if you'd like.


Maniac0301 HalfDork
7/3/20 11:15 a.m.

That's awesome.   I do plan on a centrifugal clutch I would have loved to 3 pedal the kart but I didn't want to deal with the pedal packaging and working out a mechanism.  I'm kind of guessing on the ratio's for the clutch and transmission sprocket.   I'm leaning towards the higher top end side with the assumption we can always use a lower gear if needed.    I believe the clutch I'm getting has a 14 tooth sprocket with the transmission end being an 8 tooth.   I'm using a 9hp engine so I think being geared up like that will allow me to keep the revs in check while still giving decent speed.

I see the engine is moved rearward.  That's pretty much the solution we came up with as well to get the seat far enough back.  I also plan on cutting the holes in the chassis to put the rear axle right where its shown here.   For some reason John Deere put in an extra hole and reinforcement right in that location so I'll be taking advantage of that.

Maniac0301 HalfDork
7/3/20 8:57 p.m.

We got busy today working on some very critical parts of the kart. Based on info from thread I started in the general forum the band brake will be just fine for what we are doing. The problem is the original brake was worn and a replacement band is almost $100. I found out that a lot of construction equipment along with old 1930s and 40s cars use these. A quick search on McMaster Carr got me some replacement brake material for $10 that should do the trick.

We then chopped up the old steering system and repurposed the toothed steering rack and welded a the plate in place. Eventually we will weld the rest of the steering shaft to the top of the arm we made.

Finally we got the chassis drilled for the axle bearings and axles in their final home. Pulling apart the diff we discovered its a regular open diff not a limited slip but a bit of tweaking to the grease inside supposedly helps to keep 1 wheel peals down. We now have the kart at its final stance with many of the major systems in place.  I will be putting the brake drum on the sprocket side of the diff to make room for the engine to transmission chain.

Maniac0301 HalfDork
7/7/20 7:51 p.m.

With the wider track width we needed to lengthen the steering arms to match. At the same time I wanted to add in some adjust ability. To accomplish this I cut the arms in half and welded on some threaded road. A coupler and jam nut lets me set the length and from that the front alignment and toe.

Testing it out and the geometry allows the pivots to go over-square which can cause steering to lock in one direction. I'll be cutting out the plate that the pivot is on and moving it forward in the kart

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