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In textbooks, I have read that the balancing grade of an engine is between 50% and 70%.
Some people say that the crankshaft must be balanced to 100%.
Is it just a matter of perspective what constitutes 100%?
The weight of the connecting rod is only partially included in the weight calculation for the crankshaft.
How does the boxer engine with 2 cylinders work?
If I install lighter connecting rods, along with lighter pistons, how is the counterweight calculated/determined?
Can anyone provide me with well-founded and verifiable statements?

Okay, let's hear the expert knowledge .
The background of the question is as follows:
The motorcycle comes standard with a 2-cylinder boxer engine, which will be upgraded with two new connecting rods that are 240 grams lighter each, as well as flat-top pistons for a higher compression ratio.
So far, it has worked well with the standard mass balance system, even with moderate adjustments, and often even better, as the components are balanced and the combustion chamber is optimized.
Now, practitioners and scientists are arguing about whether, in cases where a general easing of the crankshaft is not possible, balancing the crank cheeks is the technically and practically correct approach.
For clarity: 180-degree boxer engine with two counterweights per cylinder.
The boxer engine achieved nearly the same practical performance improvement (reduced engine vibrations) with the lighter connecting rods as it did with the heavier, original connecting rods. (The weight reduction of the lighter pistons is not factored into this comparison.)

Here's a translation:

"To quote something from my V6 experience: The rotating masses are 100% balanced, and the oscillating ones are balanced to about 90% after testing. Of course, this can't be directly applied, but 100% balance for the rotating components would also be plausible for a boxer engine. The experimentally determined 90% shows that the degree of balance is probably not so easy to calculate."

Thank you, Christians.
Does anyone know someone who knows someone who has ever trained a boxer?
but not KO .

Hello,

It's hardly more complicated than it would be with a boxer.

The oscillating mass forces completely cancel each other out, so there's no problem as long as you install lighter parts on both sides .

If you install lighter connecting rods, you must also reduce the weight of the crankshaft counterweights by the corresponding amount to maintain a 100% balance of the rotating mass.

Approximate formula when the center of gravity of the connecting rod is unknown: 2/3 of the connecting rod's mass goes into the rotating component, and 1/3 goes into the oscillating component.

Is everything alright?

Best regards,

Thank you, Albrecht, for the information.
I believe the lower connecting rod side is weighed when the bolt axis is placed on it, and this weight is used as a reference weight for balancing.
2/3 is approximately correct.
Is it the case that only the oscillating masses remain, namely the connecting rods, pistons, bolts, and retaining clips, and that the lighter they are, the better they perform, especially since they rotate in opposite directions?

edit: "erleichtern um das reduzierte Gewicht" - OK. What's the difference between that and precision balancing?
Is that then on the inertia flywheel (like, for example, a Schrick flywheel)?

Okay, I wouldn't simply reduce the weight of all components by the amount that the new valve springs are lighter. In my BMW R51/2, the original weights weren't exactly the same either, so you have to measure the individual components and experiment. If it's an old BMW Boxer, you also need to consider the manufacturing tolerances (which were quite solid within the frame, though).

@ Matthias
Sure, not the total amount, but as I wrote, the difference in height compared to the old connecting rod.
>New 4V R1200xx or R1150xx models.

Hello,

"Everything you're writing is correct. The lower the oscillating masses, the better/easier the engine rotates. The level of precision required for balancing/compensation depends on the desired performance."

- The weight of the pistons, rings, and bolts should be relatively close to each other.
- Connecting rods can have significant differences (including in terms of weight distribution!).

Here's how to proceed: First, determine the exact center of gravity of each connecting rod by weighing the lower and upper ends while the rod is resting on its respective opposite side (as mentioned above). Then, try to find two connecting rods that are as identical as possible. Next, create master weights that correspond to the determined mass of the lower connecting rod end (red portion). Use these weights to fine-tune the balance of the crankshaft on a balancing machine. This is a precise and reliable method.

Depending on the engine design, free moments can also be compensated for by adjusting the weights on the crankshaft cheeks (at least partially). In that case, things become a bit more complicated.

Best regards,

So, the initial balancing involves adjusting the weights to achieve a rough balance.
And is fine balancing always done with a balancing machine?