Balance

[Sh3tland]

Hello ,
Why are the balance weights not exactly 180° offset ?
(Simgle cylinder, no balance shaft)

Thanks

 

[BrianPetersen]

Presumably you mean that the center of gravity of the balance weights (the three lighter coloured) is not 180 degrees offset from the piston pin. Probably it's because the manufacturer found some benefit in not fully offsetting the first-order vibration. Why that would be, who knows. Maybe intentionally not fully offsetting the first-order vibration partially offsets other effects due to this being a single cylinder engine and thus subject to high crankshaft speed variations through the operating cycle and high torque fluctuations through the operating cycle (compression stroke takes kinetic energy out of the crank/flywheel, power stroke puts more back in).

 

[CWB1]

Crankshafts rarely have the counterweight 180* from the rod pin, the only ones I ever recall seeing are antiques designed well before modern balancing was available. Simply stated, they need to be dynamically balanced taking into account the weight of the rod and piston, compression, and quite a few other factors which tends to put the weight behind the center of rotation.

 

[EHudson]

Is the bore axis offset from the crank axis?

 

[LadaTrouble]

Looks like a 2 stroke - they would be stuffing plugs to reduce crankcase volume, increase crankcase compression.

 

[enginesrus]

If you had the photo with the rod at the top as well as the cylinder or cylinder flange it would be better to visualize it and the rod at close to tdc.
And the photo off center doesn't help either. If the darker holes or circles are with no weights, then the thicker area of the crankshaft at the 5 o'clock area acts as a weight with the lighter colored holes or weights. And any shift in position was where the dynamic balance was calculated.