Question about balancing rotating assembly
I balance a lot of single cylinder Kohler 16, 14, 12, horse motors. A lot of them are strokers with counter weights so big they have to bolt on because they won't fit through the hole in the block.
It is definitely not an exact science. The last one That I did, had already been balanced at another shop. The guy said it would shake his fillings out. I weighed everything, made up the bobweight and spun it. It was only about ten grams off, and that is subjective, as there are different schools of thought on what percentage to use.
I corrected it and when he picked it up I told him that I probably didn't do him any good.
He called a couple of days later and said it was great. I was amazed, 10 grams is not much, but they really zing those little motors. Garden tractor pulling.
I use 65 Percent on the bob weight in the bigger bore motors, a little less, but never less than 62 percent in the smaller stock class motors.
The one nice thing about those motors is that you don't have to match weigh when there is only one of everything. it is also easy to put in mallory when you can unbolt the counter weights.
This doesn't help the OP, but just adding to the fact that balancing is not an exact science and sometimes you have to rely on what you have found to work.
I went with a friend to buy a “race” KX 500 Kawasaki because I have ridden big bore 2 stroke dirt bikes since 1981 and he wanted an extra set of eyes.
We get there and the seller is leg humping my buddy to death about how the pro who did the engine was the guy who built and tuned for so and so and crap like that.
The bike was clean, but the proof is in the riding. Since I was short and fat, the dude wanted to start the bike himself, but I’ve been short and fat for a long time and I wanted to make sure I could start the pig so I could teach him to start it.
Once it was running I let it warm up a bit, shut it off and said we pass. The seller was wetting himself because my friend was a cash buyer and the seller was hard up. I said we will pass again. Then the seller say “you said it’s all about the ride and yet you won’t even ride it”. So I said my buddy will ride it, because it’s going to be his bike and I don’t want to have to ride it because he hates it.
The seller says if he’s a rider he’s a buyer. So I took my buddy aside and said “did you see how smooth that thing is at an idle” and he says yep, I think that’s a good thing. So I told him to remember that when he rode it.
He made one lap around the field, came back and said we pass. The seller was livid. He wanted to know what I said to make him not buy it. I said he can tell you ne my buddy says “it’s too damn smooth at idle”.
And we walked away.
When we got in the car he said how did you know it would shake like that? And I said when dealing with big bore two strokes if they don’t shake a bit at idle, they’ll shake your head off in the upper rpm range.
And it did. It was so far out of balance you couldn’t even ride it. Because the guy who did the work didn’t know or understand you balance those things at 60% or more over balance. If you don’t do that, they are smooooooooth at idle and will throw you off the bike if your not careful.
