Balance the rotating assembly on a rebuild?

I’m rebuilding a factory IDIT (201k miles) to replace the ailing 7.3n/a in my ‘92.
*Should I have the machinist balance the rotating assembly?*
Unless a problem comes to light most all the internals “look” good, except for two of the pistons which have a little deterioration of the top edge. After cleaning and ultrasound to check for cavitation the machinist will determine how much the block needs bored. He asked if I want to balance it when the new pistons, rings, etc come in. $400.
A little background on the machinist: he comes highly recommended by multiple parties; he has been doing this for decades and is very detail conscious; he’s always buried in work so he doesn’t need to recommend unnecessary stuff to get more work; he owns and has rebuilt IDI’s, but his primary business is gas race engines.
Recommendations?
All opinions welcome, but perhaps specify if you 1) have personal experience with multiple rebuilds, 2) have personal experience with one engine, 3) “know someone who...” 4) are blowing hot air

Balance it

I second that... Never hurts to do a little extra

Rebuilt and balanced the 6.9 this spring after a piston cracked and would not hold compression. Did not have any complaints about vibration before, but it is night and day better. Makes a engine feel like its turning much slower then it is.

Would NOT recommend boring that 7.3.

Would ABSOLUTELY recommend balancing.

Heath

The machine shop that the shop I used to work for wouldn't bore an IDI more the .020". If it took more than that, it would be sleeved back to standard.

Thanks to all for the input! And an extra shout-out to hce for adding reasons.
Balancing an engine seems like a no-brainer, but I’ve been told “all the components (pistons, rods, crank) come as matched sets (i.e.-each piston weighs the same,...) so it isn’t necessary”; of course It’s what I wanted to hear because it would save me $400.
Thanks again to all; much as I want to save $$$ I would rather hear the truth.

Now, if I could only balance my life for $400!! Heck, $4k...

Good choice, I've read accounts on here, from members like typ4, talking about before, and after balancing on many diesels; it apparently makes a huge difference.

If they say weight needs to be added to the crank, run as far and fast as you can! I got mine balanced and they screwed it right up, never using that shop for anything again.

ifrythings said:

If they say weight needs to be added to the crank, run as far and fast as you can! I got mine balanced and they screwed it right up, never using that shop for anything again.

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The only way to achieve this most of the time is if the rods were lightened for this purpose. Usually involves removing a good portion of the balance pads and polishing the beam, while keeping the weights matched on both ends. If your rods and pistons are heavier then the counterweight there is really no other option other then adding weight.

One thing I would ask your machinist is if the flywheel and damper are required when balancing. The engines are externally balanced and the flywheel and balancer must be spun with the crank. There seems to be a lot of misconceptions pertaining to the flywheel and damper balance on idi.

hce said:

One thing I would ask your machinist is if the flywheel and damper are required when balancing. The engines are externally balanced and the flywheel and balancer must be spun with the crank. There seems to be a lot of misconceptions pertaining to the flywheel and damper balance on idi.

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The machinist did request the flywheel and balancer for this reason. The flywheel I provided is off the donor engine (‘94 IDIT w/ auto trans) whereas my ‘92 has the ZF-5. Are the auto/manual flywheels interchangeable? I plan on a clutch upgrade. Does that factor in? Don’t know what brand/model clutch yet—haven’t gotten to research that yet. I’m not ******* clutches so it doesn’t need to be the best-of-the-best, just enough to handle 300ish hp—optimistically .

If what you gave him is off an auto transmission, that is a flexplate and not a flywheel. You need to get him a flywheel and not have him balance it with that flexplate if you plan on using a manual transmission.

When I got my engine balanced I brought them a turbo smf and a NA flexplate, they “balanced” everything with the smf first without modifying the flywheel then put the flexplate on and balanced the flexplate to the rotating assembly. Now they did butcher the balance job but they did manage to match the flexplate to the flywheel.

WarNose said:

If what you gave him is off an auto transmission, that is a flexplate and not a flywheel. You need to get him a flywheel and not have him balance it with that flexplate if you plan on using a manual transmission.

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Thanks for the info.
I was hoping to avoid removing my current engine until the IDIT was ready for install. Might have to buy a new flywheel...