50cc inline twin 2 stroke

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#1
Hey guys just want to talk about an idea I had. They make snowmobile engines that are multiple cylinder 2 strokes right?. What if you could scale one down and have an inline twin 2 stroke say 50cc so 2 25cc cylinders wouldn't that be cool? should rev really high too. Has anyone attempted to make such an engine? I was kinda inspired by the old 50cc honda race bike but that was a 4 stroke. It should have more power than a regular single cylinder 50cc engine maybe to make a prototype you could use 2 25cc cylinders from weedeaters? and make a prototype crankcase any ideas appreciated. I believe they make similar engines to what i'm saying for R/C purposes.
 


CrazyDan

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#2
Here's a 52cc inline twin

Would be too wide for an in-frame engine, but might work on trikes.
Edit: its 220mm (8.66") wide, might make it fit using a pulley on the output shaft and manually engage the engine to the wheel with a tensioner on a lever.
 
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#3
That's cool I wonder if you could fashion a centrifugal clutch on it or have a similar transmission to snowmobiles. You could make a custom exhaust that goes from both cylinders to one expansion chamber. The width is no more than my 79cc predator with the clutch and pull start. Do you have a link of anyone that sells that engine? or similar. It looks like the output shaft isnt very long and I wonder if it would take the load weight of a person and a bike since its probably meant for RC nonetheless it would be a cool bike. UPDATE: I found sellers for the engines quite expensive $400+ and made in China too, I think it would be cheaper to build a prototype based on it with weedeater parts.
 
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#4
Generally speaking, R/C engines are probably not all that practical for a mb, since they are oriented in a front to back configuration, instead of sideways, like the china girl or predator motors. There are many very, very cool gas r/c engines, however, and they usually make a surprising amount of power for their size. Here are a couple of neat little engines just fyi:
https://hobbyking.com/en_us/gtt70-engine.html like that one, it's a 70cc 2 stroke twin or this other 5.5hp, 53cc twin
https://hobbyking.com/en_us/5-5hp-53cc-twin-cylinder-gas-engine.html
For some reason this page on this site is acting strange, but this is the GAS engine page, no glow engines here, but they have 2 and 4 stroke engines in a range of sizes, it's a cool resource, and you never know, you might find something you can't resist, even if you can't really use......
https://hobbyking.com/en_us/power-systems-1/gas-glow-engines/gas-engines.html

Bear in mind that good old china girl only makes about 1hp, and some of these are really impressive for what they are. There is even a 10cc engine that makes 1.9hp!
Also, I would remind you that china girl has built in gear reduction, so finding a practical transmission for an r/c motor, or the motor that started this thread will be difficult. I mean, lets face it, wtf are you going to do with a 12,000rpm output?
 
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#5
Oh cool a 3 cylinder I'd like to make an engine something just sounds cool about a motorized bike with a multiple cylinder 2 stroke I have a few old weedeaters and got the idea from them, maybe I could use 2 25cc cylinders and cast a crankcase for it based off the original ones just longer then there would have to be a crankshaft made.
 
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#7
I think I saw that video the other day the first 52cc engine at the top of the thread could work you'd just have to have a longer shaft and take off the golden bracket and come up with a transmission and mounting points and you could use a wide pedal crank, the only thing I don't like about it is the price you could buy one of the 9hp ktm 50 clones for that much. But who knows they might be about the same power
 

HeadSmess

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#8
Mind your speakers. :D
Yep sounds pretty cool to me. :cool:
lol. 12.5cc a cylinder! microscopic!

the honda cbr250 is a joke. its missing three cylinders...

whereas the original cbr250RR, aka mc19-22...beast....four cylinders, redlining at 20,000 +

the sound of MAGIC! oh. yeah. i forget. they were only released in japan and australia... suckers!

now they think theyll get increased sales by making the latest version a twin...still missing two cylinders!

(or four, if you like the...rc166 wasnt it? the six cylinder?)


meh. what you want for the motorised pushy is a Vtwin...like a 1/5 harley engine...blat blat blat blat...
 
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#9
A guy on YouTube built a 175cc v twin, franz flyer he called it I think he also built a homemade 392cc v8 bike the reason im interested in a inline 2 2 stroke or even a inline 3 is thats what i'd like to put on a bike since there are very few of those type builds
 

HeadSmess

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#10
i like the idea of horizontally opposed pistons, myself... just like a commer knocker but smaller...

the challenge is getting the crank to squeeze in between your pedals. gearbox. clutch. all that jazz.

hell, someone even tried a rotary build on here somewhere... 160cc of raw rotary bwap!

the only real source of small multi cylinders is RC plane engines...and even the four strokes are oil thirsty. run on a 10: pre-mix.

which will require flywheels, clutches and that damn gearbox again.

v-twin is the best layout cus its got the best natural balance and its narrow.

twostrokes make it hard because you need either both cranks to be separate, or both pistons have to be at TDC.

be fun to use to honda or fuji/subaru/robin 25cc fourstroker on a custom crankcase...

hope you have a machine shop or youre going to be spending a LOT of money...
 
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#11
There was a picture of a 52cc rc race boat engine at the top of this thread I do think the vtwin would be cool but would it be able to be a 2 stroke? probably not but if you had a 50cc vtwin it would be 2 25cc cylinders you could probably base it off the honda gx25 but even one of those engines is expensive.
 

HeadSmess

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#12
as i said, only issue with multi cylinder two strokes is the crankcase compression. they either have to be separated, or have everything hit TDC at the same time.

its why you dont see too many multi cylinder two strokes. (and yes, they exist...i think someone got all the way up to an inline six at one point...) they end up being way too wide and the cranks have to be assembled, pressed together, with all the bearings and seals in place. not easy. every engine builder i have gone to has refused to even attempt to just press apart/reassemble a twin throw twostroke crank i have here...

that boat engine is basically two 26cc engines bolted together. its wide. or long, depending how you look at it.

even a regular single cylinder (like the honda gx25) is getting too wide to fit between your pedals, especially after adding a clutch and stuff.

another option is the twin crank setup, like the kawasaki KR series. contra rotating cranks= no vibration. inline, but the other way round...
 
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#13
Yeah the 79cc pred with clutch on it is pretty wide though I have the regular wide pedal crank kit on the bike. I can understand it being too wide for the stock pedals but mb rebel makes pedals meant for the 212s I think. I got the idea looking at an old weedeater crankcase. I still think it would be easier to engineer the 2 cylinder 2 stroke than a 2 cylinder 4 stroke you have to make a camshaft, figure out timing ect. If both pistons fire at the same time on the 2 stroke wouldn't it have more torque?
 

HeadSmess

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#14
making a camshaft isnt that terribly hard to do. if you can make engine parts, you can make a camshaft... and timing is no real challenge either. just requires accuracy in laying out and machining.

theres not much difference between having two small pistons firing at the same time or having one large piston firing...same power. same pressure. more frictional losses though. you should get more speed from the smaller lighter pistons and therefore more peak power... but the torque will remain relatively the same. ever wondered why dirt bikes prefer one big cylinder compared to road bikes with two, four, or six cylinders? its actually a bit more complex than simple torque/power...its also about the smoothness of the power pulses. dirt bikes, with their thump thump power delivery can slip...then get a break while they regain traction...then slip...repeat process. watch an old lenz bulldog tractor working under load... you can see the jerks as the single cylinder engine delivers a power stroke. for the dirt, for traction, that power delivery was far superior to the smoother running multi cylinder engines.

multi cylinders tend to spin but the firing order is (usually!) arranged (on bikes) so you get one whole revolution with all the power strokes, followed by another revolution with no power strokes.

i always found that a v-twin, when it breaks traction, remains very throttle stable. very steady. whereas a inline four, as soon as it breaks traction it tries to spin itself up to redline...scary.

car engines are designed for smoothness of power delivery, all power strokes are evenly spaced. early bikes did this too but they soon discovered it wasnt the best way to design the engines.

not really an issue with low horsepower engines, but yeah...something to think about.

and balancing is harder, unless its horizontally opposed.
 
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#15
A 78mm clutch is made for goped use on that style of crankshaft. Then you have to reduce the output thru a 5:1 pocket bike transmission making it really wide. But its possible with off the shelf parts. That engine would accept a 54mm clutch from DDMracing

http://shopping.netsuite.com/s.nl?c=885035&n=1&it=A&id=4175
But there is a fabricator I know of that makes a 78mm upgrade for high HP high revving Zenoah small bore engines 23/38cc's. And stock they rev close to 15k!
 
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#16
Oh you mean that 52cc inline twin engine? I would want a good clutch that can take the high rpms also that motor is over $400 and it looks like its liquid cooled because theres fittings on the cylinders. The shaft looks like it only sticks out an inch and that golden bracket would have to be removed. It would also be hard to come up with mounts since the bracket is part of the mount. I'm guessing the clutch may or may not bolt up to the existing bracket holes but the 54mm clutch does look like it would bolt on. I'm guessing you would need a stronger clutch spring since it is 52cc twin instead of a single cylinder 29cc. I wonder how the exhaust should be 2 independent expansion chambers or a single? Maybe hpi baja exhausts an aluminum frame would be good for a build like this. Seems like alot of money for something made in china though. Might even want to change the bearings for better ones. Maybe theres a japanese or other version since the chinese copy everything.
 
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#18
I saw there's a 58cc version of the twin we were talking about I was looking into the zenoahs maybe the 31.8cc single cylinder could be used on a bike.
 
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