Smaller lighter and quieter MB engine

[Steve Best]

A thread came up in the other forum with the idea of smaller lighter and quieter MB engine. It proposed something about 30cc-35cc. I feel it will be harder to sell the idea of less displacement to the US market where most jurisdictions specify less than 50cc and 20mph, most of us want to take full advantage of these limits. So how to make it smaller lighter and quieter?

A large weight reduction is in the flywheel. Aluminum cheeks with steel weight rings on the outer diameter could reduce weight 3-4 lbs in a standard China Girl. Thinner precision casings and plastic covers would take 2-3 lbs off and reduce all dimensions 1" in every direction. BMX chain and aluminum sprockets. These things would double the price of production.

The plastic gear and chain covers would dampen a lot of their noises. A new air filter cover and fine foam filter would quiet a lot of the intake noise. Rubber pegs between the cylinder and head fins would quiet those noises.

The exhaust would be a pipe tuned for max torque at 20mph and +50% over-rev so extra pedaling would be rewarded with up to 30mph speeds but still meet the legal 20mph condition on flat and up hills. Ideally the torque tuned pipe would be thinwall construction with a surround type muffler to quiet it to a whisper.

The beauty of this approach is that each component would still interchange with all the 50cc and 66cc motors that are still out there. Development could start as aftermarket sales of individual components as a complete package is developed.

Think about it;
meets all legal requirements, 50cc, 20mph flat speed
will haul touring weights up hills
can still pedal or down hill to 30mph
whisper quiet
half the weight due to precision thinwall castings and aluminum/steel hybrid crank
1" smaller in all dimensions
Complete interchangeability

Wouldn't this be great? Any manufacturers listening?

Steve

 

[bluegoatwoods]

Well, I like your ideas. Expense would be a problem, though. You're right on that as well.

And if the flywheel were lightened, then wouldn't vibration (not to mention poor warm-ups) be trouble too?

 

[butre]

http://www.hobbyking.com/hobbyking/store/__11973__5_5HP_53cc_Twin_Cylinder_Gas_Engine.html

it doesn't meet your 50cc requirement (barely), and it could break 20 mph if geared for it, loudness would depend on what pipe you put on it, and it's slightly larger (though how much of an issue is that really)

it is lighter, makes more power, quieter, and would have next to no vibration.

 

[45u]

Take too much off the flywheel and you will have very poor low end torque. I know this from trying this on a Harley crank and trying lighter flywheels on radio control cars. One of the reasons that Harley s have such good low end torque is there heavy flywheels. 2 storks do not have very good low end torque to begin with so I need all I can get.

 

[Steve Best]

The idea with the crank is to lighten the center with aluminum cheeks but to put a steel ring for weight at the outer diameter, which can be even larger than stock because there is more room in the case. This would drop pounds off the crank but keep the same inertial mass as the present crank. It is all about polar moment of inertia. Less weight but moved our further. The weight at the center of the crank does nothing for momentum. And I agree Jeff, these motors need all the inertial mass they can get.

 

[Deleted member 12676]

aluminum isn't strong enough. and it would only save about 1 pound anyways.
taking a few pounds off the engine won't make it any better at climbing hills.
a plastic side cover may allow more gear noise to exit. maybe not.
20mph limit sucks! I had a 24 volt electric bike that had that limit so I upped the voltage to 36 volts, which worked well.
I love speed. maybe it's just me.

If you want your ride to be lighter then stop eating so many potato chips and french fries! Most humans can easily lose 10 pounds.

 

[KCvale]

If you want to use a tiny engine best consider bike drive gearing, it would be pretty useless without mechanical advantage.

 

[AutOtaku]

I would think a BMX chain and sprocket wouldnt be strong enough for these motors.....

 

[libranskeptic]

dunno respective weights vs chinese kits, but fyi:

http://engines.honda.com/models/model-detail/gx25

as an example of whats doable:

their trimmer motor 25cc is 2.8kg & despite what the weird power number they give here (see footnotes in link), is 900 watts sustained i read elsewhere

thats a whomper by ebike power standards & needs a big heavy battery

my; 24 speed, 350 watt, 30 kg inc battery, alloy mid drive is, as fast as i need to get me to the wind barrier, and climb anything it can grip on. It would weigh about 25kg if i swapped in the gx25 (commonly used in various sizes in their trimmers, the "upside down ok" type carbys are convenient for bikes spillage wise btw)

torque issues are a transmission problem, not a power problem.

900 watts pushing a 25kg vehicle is too much if anything.

my ideal would be a hybrid with a 100-300w tiny generator, 2 stroke if need be (model aircraft/boat engines?), powering the ebike and charging the power boosting battery, and maybe a stealthy 450 watt version of my above bike, or maybe just add 2WD, using a 2 speed front hub motor as well.

 

[FurryOnTheInside]

dunno respective weights vs chinese kits, but fyi:

http://engines.honda.com/models/model-detail/gx25

as an example of whats doable:

their trimmer motor 25cc is 2.8kg & despite what the weird power number they give here (see footnotes in link), is 900 watts sustained i read elsewhere

thats a whomper by ebike power standards & needs a big heavy battery

my; 24 speed, 350 watt, 30 kg inc battery, alloy mid drive is, as fast as i need to get me to the wind barrier, and climb anything it can grip on. It would weigh about 25kg if i swapped in the gx25 (commonly used in various sizes in their trimmers, the "upside down ok" type carbys are convenient for bikes spillage wise btw)

torque issues are a transmission problem, not a power problem.

900 watts pushing a 25kg vehicle is too much if anything.

my ideal would be a hybrid with a 100-300w tiny generator, 2 stroke if need be (model aircraft/boat engines?), powering the ebike and charging the power boosting battery, and maybe a stealthy 450 watt version of my above bike, or maybe just add 2WD, using a 2 speed front hub motor as well.

Wow I did not know there were any-way-up four strokes. It sounds great if it can be made to mount to a bike, output the right sort of rpm, pedal start, look less like garden equipment and be narrow enough to fit between crank arms.