Transplanting a KX80 into a scooter.

[frascati]

It may not be the perfect motor for the application. The gearing is going to be irritatingly close. But I have it on hand and I have the scooter to put it in. So how quiet can I make this engine?

The spec is 16hp. I'd be very happy with even half of that if I could greatly reduce the decibel level and, hopefully, spread the powerband out a bit. The KX80 actually weighs almost exactly the same as the original 50cc engine and produces almost six times the rated hp.

There's little room to fit the expansion chamber, so I would just as soon put an 'enduro' pipe on it. What is the quietest muffler that I can put on this, as well as the best method of quieting the intake?

 

[brentoncole]

so is this like a stand up go ped scooter or like a moped scooter or something, when i hear scooter i think stand up scooter so if i was you i would go to like a a go-ped web site that sells miniaturized expansion chambers and just do some fab to hook up, as far as muffler on those scooters they bolt right on to the expansion chamber, noise wise i have a cr 80 and as long as i stay out of the power band(4k or 5k) it is quieter than any stand up scooter and still has more power,p.s. quiet mufflers arent really sold the quietest is what you make your self just get large spray can or weld up a large cylinder and have a perforated 1inch diameter or smaller pipe inside with glass insulation in side and maybe a tip that points down and it should be very quiet with little or no power loss, use a smaller perforated pipe for less noise

 

[Patman]

So this scooter has a chain driven rear wheel? There is vertical clearance for the engine that is no doubt taller than the typical horizontal? The chassis is able to handle the additional power? You have resolved the mounting points? Serviceing the various points on the engine will be no problem?....

 

[IndyMX]

so is this like a stand up go ped scooter or like a moped scooter or something, when i hear scooter i think stand up scooter so if i was you i would go to like a a go-ped web site that sells miniaturized expansion chambers and just do some fab to hook up, as far as muffler on those scooters they bolt right on to the expansion chamber, noise wise i have a cr 80 and as long as i stay out of the power band(4k or 5k) it is quieter than any stand up scooter and still has more power,p.s. quiet mufflers arent really sold the quietest is what you make your self just get large spray can or weld up a large cylinder and have a perforated 1inch diameter or smaller pipe inside with glass insulation in side and maybe a tip that points down and it should be very quiet with little or no power loss, use a smaller perforated pipe for less noise

Wow... really??

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Here, I had extra. You can have them. You seem to need them a lot worse than I do.

 

[frascati]

So this scooter has a chain driven rear wheel? There is vertical clearance for the engine that is no doubt taller than the typical horizontal? The chassis is able to handle the additional power? You have resolved the mounting points? Serviceing the various points on the engine will be no problem?....

Excellent points.

motors weigh almost exactly the same (kx80 actually a few oz less)
KX80 is narrower and shorter and slightly taller when canted forward.
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when canted forward a bit the more vertical cylinder fits the space quite well once the carb intake is fabbed to angle away a bit.
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It's a 1984 Puch moped.
Chain driven.
Mounting points are very easily adaptable via length of 4 inch ID U channel steel contoured to meet the motor at two points and the chassis at four points. Radiator will be hidden behind the headlamp and tubing routed along side the electrical harness.
Will the chassis handle the additional power? Of course not. Not if ridden like a KX80. If ridden like a Puch moped and detuned a bit with a quieter muffler and provided with the forks and triple clamps off of an '84 Yam 80 enduro parts bike... sure. I'll probably even mount the swingarm and rear wheel from the Yam on the channel steel motor mount I make. In which case the chassis will be stressed even less than was originally.

What's the point? This is the most fun on two wheels in more public spaces than any vehicle I've ever owned. It's registered as a moped for seven dollars and fifty cents and that sticker lasts four years. Six bucks to renew. No insurance necessary. No helmet necessary. The little step-through frame is so innocent looking and unobtrusive that I've ridden it waaaay beyond any point where a motorcycle or full fairinged scooter would be prohibited (socially if not necessarily legally), and if I've finally gone too far, I just kill the engine and pedal! I've got other road and off road bikes but this one actually makes you feel like "anywhere's possible". You just won't go "anywhere" very quickly. Fine by me.

It would just be that much more fun with more than 1.5hp. And this KX can be shoehorned in and painted black without changing the appearance of the bike at all.

Actually. The more I describe this, the more exhausted I get just contemplating it since I know how it sounds on a board like this. Forget it. It was a nice thought. I've got a full shop and very capable tig welder so it's certainly a hell of a lot less ambitious than, say, putting a larger engine in any other vehicle (which guys do every day), but probably just not worth the effort of seeking advice for no other reason than that most people think it's hairbrained. So if you want to just weigh in here with another "that's pretty stupid" comment then save it.

What of the hundreds of overchromed, uselessly suspended, structurally unstable, airbrushed monstrosities that emerge from Orange County Choppers and similar shops? Wallet drainers useless for any ride beyond pimpin for a couple of blocks of flawless pavement? And they're all the rage? Or even the hundreds of guys packing 500 useless horses under the hoods of their "muscle" cars. Where's the hairbrained? And I wouldn't even be doing this to increase the cool. I just want to extend the fun a little bit. It'd be a success if noone even noticed (in fact that's a major part of the plan where law enforcement is concerned). Oh well. Rant over. It was a fun thought.

 

[IndyMX]

No matter how stupid the idea sounds, it'd sure be the fastest moped on the street.. ;)

 

[Patman]

Glad you actually put some thought in to it. Most posts that ask if something like this can be done have gone no further than to think it would be a cool idea. I'm all for working this type of thing out. To me it's a big part of the fun.

So now the fun of making the exhaust... I suspect that will be the biggest headache / fun part of the transplant.

 

[_JOE_]

Please keep us posted with pics! And a final product video would be cool too!!!

 

[frascati]

Ok. I'll try this tenatively. Would anyone be so kind as to advise me, or direct me to a better source, for what to expect by replacing the expansion chamber on this motor with a 'standard' enduro pipe? Or even a (non expansion chamber ) muffler from an 80cc street scooter such as this from an 80cc two stroke Honda Aero.....?
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Like I said earlier, I don't mind losing performance. I'd be happy with five HP. I still have a much more powerful engine with a gearbox. Down to five HP i'd expect pretty extended service intervals as long as the tuning was right.

How to tune an extremely high performance motor like this for average performance and high reliability. Any expert advice?

 

[Patman]

I guess you should expect a significant drop it power (duh) and power delivery similar to a 2 stroke chain saw (dead flat until it's near peak rpms with a very narrow spread). The problem you will see is that the gears in the trans were developed with a specific use and power level in mind. With significantly less power the engine will be much less able to pull them. Exactly the opposite of a tractor which generally has lower power to weight ratio but massive gearing allowing it to do a significant amount of work with the low power.

 

[helio lucas]

frascati,
i do think it´s not the better idea to put a kx80 engine in that puch frame for the simple reason you could make it simple...

a kx100 engine is more long term reliable than a 80 because has smaller ports (compared to the bore) and has more potencial for silencing, power ,torque or power delivery wich means even if you do not get it rigth the 25% more cc will make the difference.

now, fuel consumption is a problem with such a small tank, a chinese pit bike engine is a great engine for the purpose. there are from 50cc to 170cc horizontal cilinder like the original engine wich will make it more stealth. they are very litlle stressed four stroke engines so reliability is not a problem.
fuel comsumption is maybe half than with the kx engine.
power delivery is perfect for the aplication.
peak power is more than suficient. if you think a 50 cc engine will not bring anything more than stock setup, get a 125-150cc lifan (zongsheng or any other good source) engine. they have some 10-15hp with loads of torque.
they don´t need a bulky exhaust pipe like a 2st engine and they can be bought for very cheap. in portugal a kx80 worth twicw the price of new pit bike engine.

just one more idea: stock engine could be modified for maybe half the time and money than to get that kx80 engine working.
in netherlands, austria and india they have a pretty good source of information.

http://www.50cc.nl/frameset_eng.htm