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Discussion Starter #1
My question concerns the "balancing" operation that a machine shop can perform when one is rebuilding an engine.

I'm rebuilding a roller-block 5.0. I've got all the machine work done and want to begin assembly.

When I picked the stuff up, I asked the machine shop guy about balancing the goods. He mentioned that it'll probably be fine to not balance and that it was more necessary on race/strip/high-rpm type cars. He also said that they'd have to press my new pistons off the rods to balance it -- as part of the work, I gave them the new pistons to press on.

I've searched here and cannot come up with a clear cut case of when it is necessary or not. I would assume that balancing the reciprocating assembly can never be a bad thing, but what criteria should I use to decide whether to balance or go as is?

The machine shop guy has been very helpful to me all along and I'm inclined to believe him. However, I don't want to start assembly and then have any regrets later.

The engine will be used only for driving, never racing. I don't think I've ever made it past 4K rpm on the current 289 and I can't imagine I would with this engine either. The crank I'm using was reground 10 under. The rods are stock 1990 units with new hypereutectic pistons to match the 30 over bore. I'm planning to buy a 50oz. flywheel eventually and either rebalance my original 28oz dampener or purchase a custom v-belt pulley for use on the stock 50oz. that I pulled with the engine.

Any input is appreciated.

Jerry
 

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Biggest thing I've noticed about properly balanced engines is lack of harmonics......even a good OEM balance will occasionally have them at certain rpm ranges...

How do your HE pistons compare to the OEM's, weight-wise.....that would likely drive my decision..

If your combo is stone stock (except for the pistons) and you don't expect to see more than 5K, I'd say an OEM balance would likely be fine.....if the pistons are substantially lighter or heavier than OEM, I'd consider biting the bullet and getting it done. You can dummy up an OEM on a stock rod and compare weights...

With the right jig, the pins can come out and go back in all the pistons/rods in a little over 1/2 hour....maybe 25-30.00. Balancing will likely run 150.00 or so...they'll need the flexplate/flywheel and damper...

Good luck!
 

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Discussion Starter #4
The new pistons are a smidge lighter than the stock ones. With this feedback, I think I'm going to have it balanced just to be sure.

Since you seem to be "in the know" in many regards, what's up with the change from 28 to 50 oz. balance? Is 50oz. better? I ask because if I go down the road to balance, I could presumably take in a 28oz dampener/flywheel or a 50oz dampener/flywheel. The 28oz dampener has the benefit of looking "more original" than a stock or aftermarket 50oz dampener, so if I could use it...

Jerry
 

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what's up with the change from 28 to 50 oz. balance? Is 50oz. better?

I don't know Ford's reasoning, but generally external balancing is done as a cost-saving measure, allowing parts to take up more space internally. IME, I can't say that any balancing type is clearly superior, although many racer's believe internal (neutral) balancing is the way to go. I would agree with this, if only for convenience.

If you were going with a lightweight reciprocating assembly, I would postulate that a balancer could convert the engine to 28 oz/in imbalance...don't know if it is possible with OEM components. I think your best bet is to contact your local balance shop and run this question by them. Personally, I wouldn't have any problems running the 50 oz/in stuff but I do understand your desire for original appearance...

Good luck!
 

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Whenever rebuilding any engine for any purpose...it is necessary to balance the engines' rotating assembly.

If it isn't done, the harmonics in the roatating assembly will
cause the engine to wear prematurely. It doesn't only happen
in high rpms....but during freeway speeds.

The balancing shouldn't exceed $150

get it done and you will be glad you did.
 
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