Fitting new VCU

Hi guys, just watched a very good video on YouTube showing how to replace VCU bearings using the existing VCU, the guy in the film went to great pains to say about marking all the components up for refitting in the same place so as not to upset the balance of the prop, fair enough I thought but it got me thinking about if I bought a recon unit then how would I go about balancing the prop?

I've seen comments about marking the shaft flanges and VCU bearing mountings in Haynes manuals etc. but I don't understand why it makes any difference?

The propshafts should be reasonably balanced from the factory and unless you have bent them, removed or added material there should be no reason why they need balancing again.

As regards the whole drive train this cannot be balanced as a whole (like a wheel and tyre would be) becuase as soon as the VCU slips (i.e. first 100 yards) it would throw the overall "mass balance" out. Hence all components should be balanced individually and the manufacturer should do that.

The VCU bearing flanges seem to have large holes - I would be interested to know if there was a balancing/centralisation process done during manufacture? I don't see the need to mark up the joints/flanges and return them to original positions unless someone knows why?

Thank you mate, your reasoning does make perfect sense, cheers!

No need to mark up anything, props or VCU. As said all props are factory balanced. The VCU can't be balanced as it contains fluid that doesn't completely fill it. This fluid will slowly settle to the bottom of the unit when stationary.
The VCU is suspended in soft mounts to damp out the out of balance forces until the fluid distributes it's self evenly due centrifugal force.