Custom Mini-Bike Engine Question

[Pure Mechanic]

I recently have started a project to, make a custom from scratch mini-bike i have started i currently have found the steel and welded it and have made the frame it looks nice right now, and i am ready for the engine. i have made the frame big enough to fit a pretty good size engine in the frame.

well my question is currently, what's the biggest maximum performance engine i can put in this beast? i was thinking about a snowmobiling engine because that would be great performance but please give me your thoughts i will use yours not mine, most people on this site know what they're talking about. i am making a beast from scratch and hoping it will be a monster in the future and easily glide past 60mph +

 

[buckeye]

Needs some idea how big this beast is. Got some pics.

 

[texasfabguy]

Pictures would help.

 

[paul_probus]

I would add that the pictures should have a yardstick showing the height and length of the area the engine/TAV/Jackshaft would go in.

Paul

 

[Mindhacker]

If you want to run a torque converter that's probably your limiting factor, there's only so much power they can handle.

 

[Squisherton]

If you're going to want a transmission you're limited to which ever motor/trany combo you come upon. If not and are ok with a single gear, then you need to show some pics of this frame. There are some GIGANTIC motors out there but there are also some smaller motors that can keep up/out do some of their big brother counterparts.

 

[texasfabguy]

Best bang for the buck is big motor and a good clutch. For what it would take in aftermarket parts just to get 2/3 the torque of a 420 cc you would spend twice what the 420cc cost.

Even with gearing to over 70mph it will still pull hard on take off.

 

[paul_probus]

Oh, and you broke the first rule: Have all the parts you need FIRST. :hammer: Much easier to build around what you got, vs. trying to add them in later. :drinkup:

Paul

 

[Oldsalt]

Tex has it right as far as I'm concerned. "There is no replacement for displacement". A big motor will produce more USABLE power than twice the money spent on a small hot-rodded engine. And will be reliable. I have a 'big block' in a slightly stretched Alexander-Reynolds. It is a blast to ride, reliable, easy to start and looks mean.

If you end up using a, say, 8 HP stock motor [like a Briggs or Tec or whatever] it will be necessary to run a jack shaft. If you put a clutch on the motor and a sprocket on the rear wheel and then line them up the big wide motor will be hanging out way too far on the right side. Generally it is best to have a longish frame to accommodate the jack shaft behind the motor and have some room in front of the engine so there is a place to put pegs.

 

[paul_probus]

There's also no reason to be wedded to the generator engine/clutch or TAV/jack shaft drive system. The clone Honda dirtbike engines up to 200cc's are available inexpensively. Of course you could also get a used genuine dirtbike engine which you can get larger and also have the choice of going 2 stroke.

Paul

 

[The Restore Kid]

Probably honestlty bang for buck small engine horse power is going to be an old junk slowmobile.. You can usually find some old junker Artic Cat for 250 bucks that runs strong as hell.. Then ya already have your 440 CC two stroke engine, with matching torque covertor drive system.. Take out the parts ya wany, scrap the aluminum tub for 35 bucks of your money back.. :shrug:

Or you can spend thousands on the most ridiculous small engine you can dream of, and have a Briggs or Honda OHV that makes the same amount of power for 1/4 the weight.. But you're stuck trying to rig a chevy cavalier clutch into the bastard so your not blowing stuff up..

And you're back to square one.. :lol:

 

[Cyanide]

find a cr500 or kx500 these are about briggs 5hp size but are 500 cc 2 strokes!! lol ive thought about doing it

 

[texasfabguy]

There's also no reason to be wedded to the generator engine/clutch or TAV/jack shaft drive system. The clone Honda dirtbike engines up to 200cc's are available inexpensively. Of course you could also get a used genuine dirtbike engine which you can get larger and also have the choice of going 2 stroke.

Paul

do you see any jackshafts in these pictures?

don't try and down play something you know nothing about,if you ever rode a nicely built big block bike your arms would be about 2" longer than they are...or your head mite have a flat spot on the back of it.
In my opinion,mini bikes with motorcycle engines are really just small motor bikes with really shitty suspensions.:no: