Engine Blue Printing

[Benny]

If you do re-build an engine, you have to re-balance all the reciprocating parts anyway, but there are different levels of balance, both static and dynamic.

If you drive a standard MX-5, then one with a well balanced engine, you will easily feel the difference.

The standard engine is a bit rough and has some vibrations, especially in the high rev range, but a well balance engine will be quieter and smoother.
The smoother an engine runs, the higher you can rev it without doing damage to the motor.

When I was into building and flying model helicopters, I always took a lot of time balancing every single rotating part.
I have a little machine that I use for balancing these small parts, called a High Point balancer, which is basically a stand where you can lay shafts and gears etc. on it.
The item rests on and between 2 large wheels on either side which allow the part to rotate with very little resistance.
You lay the main gear, for example, with the main shaft, after making sure with a dial gauge that the shaft is 100% true, and rotate the part slowly, and when stopped, I would mark the high side of the gear.
I would then repeat this a few times to see if it stops in exactly the same spot every time, or if it stops in different places.
If it always stops in the same place, then I know that the lowest part of the gear is heavier than the top part, so I remove a little bit of material each time until it stops in different places each time I spin it.
This tells me that the gear is perfectly balanced.
Now in a car, a bit of unbalance is not too critical for normal use, but in a helicopter, if something is not perfectly balanced then the machine will shake and this shaking can rip a helicopter to pieces.
I once had a blade let go in mid flight, and within a fraction of a second, the whole machine, including the thick carbon fibre frame and even the tail boom was ripped to bits.