New Member, 18hp Twin Project

#1
Hey guys! I'm new here. Thought I would share my next project. I recently picked up a 18hp briggs opposed twin for my go cart, I had to put a new valve seat in it, but it runs good now. But I got a different motor for the go cart, and now I'm getting ready to put it on a minibike. Sorta, It will be a large minibike.

But first, Heres the bike I built for my friend, Built from scratch.
8hp Honda, Tops out at 40, and it takes off so fast you almost slide off :thumbsup:

And the go cart, still in progress, this is an old picture though

Andddd the motor


I picked up the one with handle bars.

I would have built my own smaller frame and everything, But I figured that for 50 bucks, I get a good set of wheels, a good front end, and swing arm, Since I wanted a soft-tail bike. brake disc ect. When I can hardy get a wheel that I was wanting online for 50.

I got there, and found out that its shaft drive. But I found out how to take the gear box for it off, and I will be able to use it fairly easy, So no more chains for me!
I plan on building my own frame, but use part of the back of the frame, and the front end of course.
I was wanting to shorten the wheel base, to help kinda stay with the minibike bike idea, BUT with the gear box and the opposed briggs being so long, I will have to lengthen the frame most likely, :doah:

This week is spring break, So expect to see some major progress.

Tell me what you guys think, and ideas on what way to go with the bike. and Ideas that might help me shorten the wheel base.
 
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Vaxian

New Member
#2
Use the carefulness!

Man, that's gonna be a screamer!

Can't say as I would go quite that bonzo though I have been thinking about putting s 2 cylinder military surplus engine on a Mini Bike.

Keep us posted and MORE pics please! (As you work)

Nice looking Go Cart also! :thumbsup:
 
#3
Yea, I will be defiantly taking lots of progress pictures!
The shaft drive should be interesting, But I think It will be well worth it, in the end. I hate dealing with noisy chains, having to tighten, loosen. This will be smooth, quiet.. I cant wait

Also, Do you guys think it would look bad if I tried to put the engine a couple inches outside the front of the frame, I'm trying to think of how to at least keep the same wheel base, I don't want it to be too long.
 
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#6
Ok, Now
Progress, Right now Im taking a short break, For ebay AND food. .... lol
So heres the frame before I started cutting


Heres the gear box that I'm going to adapt a driven clutch onto.

AFTER my first cuts...
Replacing it all, in sections, so I can keep everything square and straight.

The Undesirables.
 
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#10
It's always fun to see what you can build from old stuff that is just lying around. :thumbsup:
Haha yea, I was wanting to build a true minibike, but turned out this was cheaper, I'm hoping it will run fairly fast. You think with a torque converter it will be able to run 50 easy?
 
#12
Assuming the other gearing isn't halfway into outerspace, I'd be willing to bet it could do a lot more than 50 easily.
Yea I hope so. Since its shaft drive I have no idea what gearing is from the gearbox to the wheel, So Im hoping it will work out ok.

Got the bottom rails mostly welded, go to weld the bends up still.
But I sat the engine in there for fun, Hopefully I will have the engine plate in there by tonight.



And I have to get a shorty oil filter for the engine to fit where it needs to go.

I was going to replace the top half of the frame, but decided to keep it for more strength, my design to replace it was a single rail going to the top instead of two, but two will be stiffer, so Im sticking with that.
 
#14
hey man...... cool project. im liking it a lot. i have one question though..... what kind of gear box is that.....?
It was attached to the engine and transmission before, I just pulled it off. I have to make a plate and oil fil port for it, and make an oil seal around the shaft, but it should work well for this.
 
#17
I cant really tell for certain but it looks like a Yamaha xs750? The stock motor probably made around 65 hp. Isn't the point of an engine conversion to increase your power to weight ratio?
 
#18
Ok guys, got a camera, Hurry for halfway decent pictures!
Haven't done anything to it lately, I need to hit tractor supply for a few things before I proceed, and also pick up the shock I just bought.











Yay Progress.

Making room for the shock



Upper Shock Mount








Bottom mount tacked,



Welded



I had to reweld the top mount several times. I had to adjust it so its sprung a little high to compensate for the motor, gas tank, transmission and rider weight.


And I might still have to move the top around some more. I will figure it out later when the engine and everything is bolted on.
 
#19
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