Question about balancing rotating assembly
So you’re ok to pay someone to balance the rotating assembly and they do that?
Luck would have it my **** would shake. Can’t tell you how many balance jobs I’ve had to correct. A bad one was a BBC that the moron who owned changed out the fly wheel from external to internal balance and didn’t think to even look at them before he swapped them out.
I forget how far off that end was, but I couldn’t even spin the crank to 100 RPM before the crank was jumping out of the machine.
I call the idiot and verify that was the FW he used in the car. He says yep. I say did it shake? He says smooth as butter.
He was either lying or stupid, because I had him bring in the main bearings because his dumb *** took it apart and sure enough, the mains showed distress.
But it was smoooooooooooth as butter. Right.
What I'm saying is people talk about engine balancing as if it is an exact science that is achieved by 'their machinist' if they ask for it. And the more they spend, the better the balance. I used to get a kick out of guys who would spend 'extra' to get the engine balance within 1/2 gram instead of the standard 1 gram.
Most balance scales aren't that accurate - certainly not the beat up ones I see in auto machine shops. And most of them, if you weigh a part 10 times, will give you 7 different values. Which is correct?
Then there is the issue of bob weight....you can change that at will and arrive at some decidedly different balances. Who knows which is perfect? None are perfect.
You can be in 'perfect' balance at one RPM and out of balance at another. Which do you use?
And who knows how to assess the exact amount of weight of the oil that is sticking to everything? No one here.
Who knows how to figure in the role of torsional harmonics? Don't forget, the engine is connected to a long skinny line of gears and tubes and rods, all rotating. No one here knows how, that's who.
Who knows how to figure in the effects of harmonics from the combustion events? No one here.
All those things play a role....but we're gonna instead worry about weighing everything down to 1/2 gram.
The bottom line is any reciprocating assembly - such as an engine - is going to abide by the old adage 'good enough' when it comes to balance. Not 'perfect'. Just 'good enough'.
Want proof? Look under the hood of the most expensive Lexus, Rolls, Mercedes, etc. Those guys live and breathe smoothness....if anyone knows how to balance and engine, it's them. Do you see their engines solid-mounted to the chassis? Hell no. They all have very sophisticated and expensive mounts that use rubber, silicone, springs, and all sorts of tricks to obtain smoothness. They wouldn't need to do that if the engine was in perfect balance.
