340 Rotax Kart - Done

[KILLDOZER]

Sorry its not a log - just the more or less finished Kart and a few build pics.

I built this for my kids - but even with a throttle stop - it's too loud, nasty, and powerful for the little guys. They're actually a little intimidated by it, so I will be building another, more kid friendly one for them. This one went the way it did because all major components were free - including the primary issue according to my kids: the engine..

Build sheet:

340 Rotax twin c/w entire snowmobile CVT, chaincase and jack shaft, steering rod assy's, steering shaft, steering shaft bearing, and brake all from a '76-77 Skidoo Tn'T.

Tires, steering wheel, original seat, from a lawn tractor

Scratch built 304ss header made from BW elbows

Modified glasspack muffler

Spindles made from original J spindles off a lawn tractor cut and welded onto 1" pipe utilizing aluminum bronze flanged bushings. These turned out excellent, and they are nothing more than a cut up J spindle and a 4" pc of pipe and 2 bushings. the wheel is retained on the shaft, and the spindle in the clevis with the very same retaining rings that were used on the tractor. It literally takes 3 seconds to pop off the wheel, or the spindle.

I cut the entire sub frame off the Skidoo, and welded it onto the cart frame. You can see I left only the basic structure to mount the engine, chain case and jack shaft. This retained all the factory Bombardier mounting points and adjustments. This set up made the entire drivetrain install a snap.

Here you can see the finished assy. I raised the rear of the subframe high enough off the frame so as to allow the jack shaft to line up perfectly with the pillow block bolted to the right frame rail of the Kart.

The jack shaft is the original track drive shaft with the track sprockets turned off, and one end turned down to 1" dia for a chain sprocket and pillow block.

Here it is almost done:

This thing accelerates like a rocket! There is a 2:1 stepdown in the chain case, and I stepped the jackshaft to axle another 3:1. The wheels are 18" turf tires. The brakes are ultra powerful as all that stepdown gives the caliper a huge mechanical advantage. I don't know what a late 70's 340 free air Rotax twin makes for power, but it's more than enough!

All in all, this Kart was ultra easy to build, and a very enjoyable project. I'm looking forward to the next one, a more tame Kart for the kids.

 

[r97]

looks awesome, only thing with brakes not directly on the axle is that if your chain falls off your done. still, sweet build!
seat?
floor pan? lol

 

[bighead]

You just gave me a bunch of ideas for I have parts sled laying around.

How does the two stroke engine run with no expansion chamber?

Also how does the sled disk brake work? I know the sled brakes are really small for some reason. Will it lock the wheels up on pavment?

 

[r97]

the sled brakes are small because with a huge track going through snow it doesn't really wan't to keep going for too long any way.

 

[sideways]

Very cool! You know it going to be fun when the engine takes up 1/3 of the vehicle!

How does the two stroke engine run with no expansion chamber?

Any 2 stroke will run with out an expansion chamber, most will run just fine but have less power. His might not of even had them when it was new.

Thanks

Hayden

 

[KILLDOZER]

looks awesome, only thing with brakes not directly on the axle is that if your chain falls off your done. still, sweet build!
seat?
floor pan? lol

I doubt the chain will ever break - it's a double #40 chain, with dual tensioners. The sled weighed 400 lbs - the cart weighs less than 100. I'll be putting something under where your feet go.

Brakes are very powerful - I haven't tried it on pavement. There is a lot of mechanical advantage helping that single caliper (it's mechanical) stop the Kart

And no, there was no expansion chamber on this engine - just a 2 into 1 header and a huge muffler. I might have to do up a different muffler set up on this one - the glasspack is fine at idle - but it's brutal at WOT.

 

[bighead]

Yah I was wondering about the Pipes for I have this old sled engine. The last owner made this exhuast set up. He used a square tube for the chamber. The ran the silencers off that. I have not ran this set up yet.

Wonder if it would work?

Hayden, Thanks for the info. I thought all 2 smokers needed a chamber. I would have used this motor on my current Odyysey project. But I thought it would not run right with the way it was.

The silencer in the first pic is on the wrong way. It should point the other way. Leaving room for a seat.

Killdozer, Perhaps you can take some ideas from these pics. Maybe two silencers would quiet it dowm some. I love your kart. Great job

 

[bighead]

I doubt the chain will ever break - it's a double #40 chain, with dual tensioners. The sled weighed 400 lbs - the cart weighs less than 100. I'll be putting something under where your feet go.

Brakes are very powerful - I haven't tried it on pavement. There is a lot of mechanical advantage helping that single caliper (it's mechanical) stop the Kart

And no, there was no expansion chamber on this engine - just a 2 into 1 header and a huge muffler. I might have to do up a different muffler set up on this one - the glasspack is fine at idle - but it's brutal at WOT.

Any chance to use the original exhaust??? I know what you meen about big. I was able to use mine in a Odyssey. But yah they are huge.

 

[KILLDOZER]

[/B]

Any chance to use the original exhaust??? I know what you meen about big. I was able to use mine in a Odyssey. But yah they are huge.

The original 2 into one header pipe stuck straight out in front of the engine - so far that I would have had to add almost another foot to the length of the Kart to maintain the reasonable seating position. I made that header to keep the pipes close to the engine, so the seat could be as close to the rear as possible. So many sled engine powered Karts end up being like 8 feet long, I wanted to keep this one as short as possible. The original muffler was rusted out, but it could have been modified and used.

 

[KILLDOZER]

Bighead, is that a car muffler on your odyssey? How does it do at keeping the noise civil? I was thinking of swapping on a small OEM automotive muffler on mine.

 

[bighead]

It is the original pipe and muffler from the Yamaha 340 sled. The header pipe I just cut ALL MOST all the way off. Then bent the cut part down and added a elbow.

once the pipe was angle down I could use the original pipe and muffler at a different possition. On the sled the pipe was going out the back on the left side. As you can see I turned it up.

 

[Doc Sprocket]

Killdozer, that's pretty funkadelic! Betcha it goes like stink. Any idea what your top speed is?

 

[KILLDOZER]

Killdozer, that's pretty funkadelic! Betcha it goes like stink. Any idea what your top speed is?

Thanks! Top speed should be around 100 kph assuming no overdrive on the CVT, and that the engine will turn 8000 rpm. I could have geared it for more top end, but I've only got 4 acres or so to boot around on, so I geared it for acceleration.

 

[Doc Sprocket]

JEEZ! Bring yer helmet!

 

[Routy]

i was wondering if this thread was still going. I want to see this kart finished and in action. im building a cart just like it. And snowmobiles are hard to stop sometimes also depends on the snow though.

 

[r97]

Every sled I've owned had vented asd slotted rotor with a huge dual piston Brembo caliper, When your going threw a field at 100+ mph it actually takes ALOT of braking power to stop that.

well thats what i get for "hearing" stuff from other people, , oh well, now we have the correct info, but that leaves the question the op asked.

 

[bighead]

Every sled I've owned had vented asd slotted rotor with a huge dual piston Brembo caliper, When your going threw a field at 100+ mph it actually takes ALOT of braking power to stop that.

The caliper on my 83 yamaha sled is tiny. Tiny like the in the above pics. I am thinking tyler must be talking about newer hi po sleds. The 80's sled caliper on my sled is not much bigger than a bikes caliper.

Here is some pics of the sled I have. To me it is really small and was wondering if it would even work on a kart. Looks alot like the OP's caliper. when I first saw it I thought no way this caliper could stop this machine. There must be other forces envoled. Looks like a pair of scissers.

That being said I know little about sleds. This is my first one and I just pulled the engine out. Killdozer can you post a pic of your brakes? I am needing to know if your set up is the same as mine. These pics is why I asked you how your brakes work on pavement.

Thanks

 

[r97]

only sled i have ever sean and it was setup like this, see the little peice of carpet that gets shoved against the driven, lol.

 

[Routy]

thats a horrible braking system r97 lol no offense. my snowmobile has disk brakes and caliper. here are some pics.

 

[Doc Sprocket]

R97- I think I mighta just got tetanus from that thing!