Projects (PROJECT) old skool twin-engine Rupp kart build...with a twist!

Hello all,

Newbie here that could use some assistance on my latest project. It's a '63-'68 wide-hoop Rupp Super K. I found it on CL locally. A kid had it but needed to sell to finance his first car. It had a clone on it that runs good, drum brake, and about 90% of the hardware is original. I picked it up because the frame was straight, and with the exception of one of the motor mounts and some other small brackets, it wasn't too molested.







Of course then by brother borrowed it. About two weeks after buying it, he went to start it and the throttle was stuck wide-open. It went flying across the yard and hit the neighbors concrete foundation. There goes my mint frame. Just some minor damage, though. I found a body guy who straightened out a friends boat trailer after an accident. He put it on the rack and straightened it out.

The carnage:


See how this wheel is straight?



Now here's the bent side



Not too bad, but bad enough. Here's a front bumper the kid added. I changed this out with a more correct nerf bar.



Boogered motor mount. I had a complete (but also bent) Rupp Dart frame with a good mount that I swapped onto this one.



Other mount is good, though.



So I stripped down the frame, got it to the sandblasters, and got the frame straightened. My plan was to set it up with twin 2-strokers, but I was also considering the motor I had ready for another project-a vintage twin-cylinder Chaparral snomobile engine.

This is not a nut and bolt restoration. It will have a real retro vibe (metalflake paint, tuck-n-roll, pinstriping, etc.) but be built with newer, better parts. I've been using parts I've had for other projects, and I definately didn't want to use some rare McCullochs that I'd be too scared to run. Was considering maybe a newer motor, like a Stihl or Homelite. Then I saw a couple of people on another site using a fairly common, newer 2 stroke that has lotsa CC's, would be easy to make power and still have access to parts...

 

LawnBoy Duraforce LAWNMOWER engines!



What? A lawnmower engine? It's a vertical shaft! Well, it's actually a great choice. It's a reed-ported 141cc dinger that is very stout, readily available, but most importantly-it's different! However, it hasn't been easy to make 'em work. Most everything needs to be modified/fabricated, and with twins it takes twice as long and costs twice as much. But I'll get into the details later.

More on the frame...

 

Tore into the frame.






Got into that front nerf bar that was driving me crazy. If you look at the frame on the far side where the bracket from the spindle mount meets the main rail, you'll see a gold color. That's the original gold metalflake under the green! Pretty sweet color!



Hacked off that boogered mount. Took about 30 lbs off the frame.



I cut a motor mount off the old frame to replace it. More on that later.



Bad news. 2 of the main rails were pretty rusted under the mount. Take a look.



Had to section out the bad and replace with new without taking the frame apart. Took care of it after it came back from the blasters. Stay tuned.

While I was at it, I made the new front nerf bar. Cut off some tubing from the scrap kart.



Cut them to length, welded them together, fishmouthed the ends, and attached it to the frame. Viola!






Not much left of the 1st frame.



This is my 1st attempt at welding/fabricating, so I could really use some advisement and guidance. I'm restricted to a 110V gasless MIG.

Some more grinding and it was off to the frame shop and the sandblaster.

 

The frame back from the blasters. Turned out great.



Back to the cancer on the rear framerails.

BEFORE


AFTER


My welding skills are gettin' there. This is after about 15 sec. with a flap disk.



Added some reinforcements for the rear frame section. Rupp frames have a tendency to snap just behind the seat. These extensions (when gusseted) should eliminate any possibility.





Also completely re-engineered steering. The old front-steer setup gets in the way of your feet so I converted to rear-steer. Used 1.25" 1/8 wall on the upper and lower steering shaft supports so I could run bearings. Didn't turn out too bad. I think I may need to crisscross the tie rods to minimize the Ackerman. These tie rods are off a snowmobile I diced up a while ago...they just happen to fit.

 

I was originally in contact with someone who was going to fab a new mount for me, but after waiting for a few weeks, I decided to take a look at the two mounts I still have.



Both are kinda rough, but I thought the black one would work the best. I know some of you are saying "why is he so worried about the plate? It'll be covered by the motor mount." Well, I'm not sure how much of the plates will be visible, so I'd rather be safe than sorry. Besides, I'm enjoying the practice!

Hacked the frame off close to the mount to make some room. Lotsa cutting and grinding ahead!



After some time, I got the mount cleaned of all that mess. Now I gotta deal with the second set of mounting holes I drilled back when I was 12. Someone told me that welding wire does not stick to copper. So I hammered a little piece of copper pipe flat and clamped it under the hole to be filled.


And Viola! It worked like a dream!

And after a few minutes of grinding, my pre-teen hack job is gone!


Finished up the other three holes and spent some time cleaning it up. Didn't turn out too bad.





Also did some cleanup on the frame. The sheetmetal seatback and sides were just tacked in a few spots around the perimeter. That seam will be visible, so I ran a continous bead and ground it smooth. Took my time and didn't warp the sheetmetal at all.

 

Most all of the frame fab was complete at this point. Had to throw on the rear axle so I could square up the new mount so I took some glamour shots. Nice to have her close to a roller!





Probably not the rear axle I'm going to use. Stock is 36", which is too narrow for the twins. This one is a 41", which is way too wide I think. After some measuring, I can squeeze a 38" axle in and just clear the recoil on engine #2 by about an inch. This pic shows just how wide the axle is.

 

Great....now I want one.

 

Now onto the motors. Tore 'em off their respective mower decks-now time to size 'em up.






Of course the biggest obstacle were the cranks. So I tore both motors apart and sent them out to be machined (thanks again Tim!). Had them shortened, turned to 3/4", had keyways cut and drilled/tapped the end for the clutch bolts.

BEFORE



AND AFTER






Had .035 milled off the cylinder heads as well. Stock compression is 5.8 to 1. Not anymore!

BEFORE


AFTER (gotta look close)


Then it was time to put the short blocks back together.



For carbs, I'm running Tillotson 334B's and for clutches I went with Noram Stingers. Also picked up the full range of engagement springs-who knows where these motors will come alive!

 

Step one was to get the carbs mounted to the block flanges. This requires some mods to the block and carb itself. I wanted to get this done first so I won't get metal shavings inside the new motors.

Need to get a vacuum pluse for the diaphram pump on the carb. Here's how I did it. Drilled out a spot on the bottom of the block (within the crank enclosure) and tapped the block for a pipe nipple.




Pipe nipple installed (with Loctite gasket maker to seal it up)



Made studs from the original LawnBoy carb screws



Ive added a Phenolic spacer for a couple of reasons. It cuts down on heat transfer from the block to the carb, but it also gave me an easy way to transition from the square bore of the block to the round bore of the carb.

If you look down the gullet here, you can see where I had some transition issues.



After some careful grinding with the trusty Dremel tool on both the spacer and the intake bore wall, I was able to smooth out the bore dramatically.



Could I have really hogged it out? Probably. Just don't want to get into too many mods right off the bat. I'll get 'er running and then work on increasing performance.

Also had to elongate the carb mounting holes. The bolt spacing on the block was just a bit narrower than on the carb. That also moved the nuts closer to the body of the carb. Had to do some clearancing on the sides of the carb body. There's not much meat in this area, so I had to be very careful.



Viola! All mounted up, ready to go. Got the other one done too.

 

That is really cool! I ran karts up and down the west coast from 1982-88.
We ran 100cc yamaha engines, specifically made for karting. They r still used today, so parts are avail.
Since your build is not nut n bolt correct, a yamaha would work. I think they put out about 17 hp in stock condition. Depending on rear gear top speed can run from 35-135 mph.

 

Got the rotating assemblies together. Everything went together perfect. Rings were all gapped perfect right out of the box. Guess it pays to buy genuine OEM parts.




Next up-the motor mounts. I'm going to fabricate "L" shaped motor mounts out of 1/2" aluminum so I decided to make some mockup mounts out of 1/2" MDF



Cut up a couple of aluminum oxygen tanks to get some material for chain/clutch guards.



Obviously, the larger tank sections won't work. Though maybe a small section of them, like an arc, could work.



However I think these smaller tank sections fit perfect!



Cut them in 3" sections. About 1/2" deeper than the clutch depth.



Thanks to my boyz Jeff & Keith for the help. My camera died so the next few pics are cell pics.

Motors settin in the frame. Trying to determine fore/aft placement. That's the money shot right there!



Actually, THIS is the money shot!



This'll give you a better idea on mount design.



Got the mount design finalized.






Also made some headway on the exhaust. I took a motor with a spare Rupp frame identical to mine to EMC, our local motorcycle/snowmobile junkyard here in SE Michigan. Spent a couple of hours looking through two barns of expansion pipes. After mocking up probably a hundred different pipes, I think I found two that'll work.



They are a couple of pipes of Kawi KX60's. Of course they'll be heavily modified, but their chamber shape and size will fit in the small space I have. Plus, they had silencers too! He had a dozen of em, so I picked up the two nicest ones.

Now before everyone starts posting with the science of expansion chamber design and how these pipes are too small for these motors, let me explain my reasoning. It's simple...it's the lesser of two evils. I don't want to run straight pipes or can mufflers on these motors. And I'm sure these little chambers will provide at least a little performance increase over straight pipes. And any pipes over 100cc were waaay too big for this kart.

Plus, they'll look sweet!!

 

sorry bud we only care about cars here...


also who gives a shit its a fucking go-kart what are you 12?

 

That's awesome!!! I wanna ride...

 

So that's where this project stands right now. It's taken me two years to get to this point (2 job changes, 2 moves, 3 kids...you know the drill). I fund the project by picking and flipping vintage go kart and mini bike parts. The mounts are currently being drawn up on CAD (buddy's a prototyper). It's more of an after-work project so it may take a few weeks to get them all whittled up. Then I need to find someone to TIG 'em together. In the meantime I'll start working on the exhaust.

Any comments, suggestions, etc. are greatly appreciated! I'm going to need help with several items (sourcing parts, bodyworking tips, etc.).

 

I knew that was coming... I still wanna ride.

 

No but apparently you are.

 

Awesome, The ole I'm rubber your glue defense... I like the new guy.

 

Thank you sir. I considered Yamahas, but initial buy-in was a little too much. One of the mowers I pirated a motor off of was my personal mower, and the other I bought on CL for $50. Plus, the cool factor can't be denied!

 

I've heard worse. I'm a used car salesman.

 

Dude.....WTF is that avatar !!!!!! F'in creepy.. Looks like my mother in law..lol

 

Personally, i think it's pretty damn cool!!

 

It is a cool project and should be a lot of fun, but seriously, this is a traditional hot rod a custom site, and while Im sure people here would like to see it, its just not the place, and theres other forums that would gladly accept it.

Im not trying to be rude or anything of that nature, but this thread doesnt belong on this forum, with all due respect.

 

Triple bitchin'!

 

Looks cool. Enjoying the hell out of the build. I think it does belong here. We Never hear about anything else but hot rods here do we? Nope, no mini bike stuff or getting married or where to go on vacation, etc. Lighten up Francis.

 

I don't know - we tolerate a lot of questionable "car" threads on here so I think it should stay open. I think it's cool because of the fab and the twin install is inspired as well. I'd rather see nice, clean fabrication on a project like this than gnarly, rusty old ratty crap like a lot of the stuff that's floating around the HAMB.

Steve

 

There's always one
carting is how I started this obsession with modifiing something someone else thought was done. Me and My brothers raced all over the NW in 58-59 and 60. Twin Mac"s were the best setup then.
My vote is keep going

 

Subscribed.

I am digging it.

Thought it was going to go downhill fast as I would have rather have seen an absolute restoration on that cart, but you are obviously trying to do it right and keep with the original theme to an extent. Your skills taking photos and documenting the fab work are better than most new guys here and are appreciated.

I admire what you are doing and hope the thread stays open. Can't wait to see some youtube video of the finished project.

 

Wanna be Moderators suck...and generally still live in their parent's basement. I want to see some doughnuts!

 

You know what I am sorry I take back my assholish comment, I'm just in a pissy mode cus I'm block sanding.

Long live go-karts!

 

great job.... makes me want to get out in the shop and make one.... my gf's daughter would love it..... subscribed here too.....

Roy