New pistons / re-balance?

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360moparjunkie

360moparjunkie

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I've changed pistons out myself thus far.
Read that the rotating assy. will need to be re-balanced?
I don't understand if this is true or not.
This is not an 8,000 rpm engine. Lucky if it sees 5,800 rpm.
Do I need to balance this engine now / or am I ok?

Thanks for the continued support of members! :-D
 
Not sure I understand why, but if this is a NEED and not a WANT then I will be on my way to the balance shop before this gets buttoned up.

What parts other than the internal reciprocating/rotating parts do I take to them?

Does this mean that the motor needs to be intenally balanced?

Can the motor be balanced and still use an external balancer?

If both are an option whats the difference both performance and cost?

Please help continue to straiten me out here. Still soaking all this in.
 
360moparjunkie said:
Not sure I understand why, but if this is a NEED and not a WANT then I will be on my way to the balance shop before this gets buttoned up.

What parts other than the internal reciprocating/rotating parts do I take to them? It depends on the torque converter you're using. If it's a nuetral balance convertor you need to bring your aftermarket flexplate (B&M makes one for this application) your crank, rods, pistons, pins, pin locks, rings and harmonic damper.

Does this mean that the motor needs to be intenally balanced?

No.

Can the motor be balanced and still use an external balancer?

Yes.

If both are an option whats the difference both performance and cost?

To internally balance a factory external ballanced engine will require a nuetrally balanced harmonic damper and the machinist will most likely need to add plugs of heavy metal to the crank counter weights. This is very expensive and really not necessary in your application.

Please help continue to straiten me out here. Still soaking all this in.
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Good questions, don't be embarrassed. Unless your using stock pistons, the weight and hence the balance have been changed. Running an out of balance engine is hard on your bearings, crank, rods, cam, cam chain, etc.
 
I do not have the auto trans. yet.

Can I get the b/m flex plate to send to the balance shop now and p/u the neutral balanced torque converter later?
 
Are you just changing one piston out?

Also when you do get your stuff balanced make sure you get a printout of all the specs so if you burn up a piston you can order one and re balance the one piston to spec.

As a safety measure it's always good to order 10 pistons so you have extras. But since you say this isn't an all out race engine ordering extra are probably not necessary.

If you have an internal balanced engine evrything needs to be neutral. If you have an external balance you need to have weighted balancer, flywheel/torque convertor.
 
If you weigh a piston you changed against a new one and the difference is within a few grams you will be ok. internal balancing probably will not take expensive mallory metal as most new pistons are lighter than stock. Sorry to disagree Ramcharger but this is a low rpm stock build and if pistons are the only change the pads could be ground to match if the pistons are close to each other with just a scale if he has an old piston.
 
You MUST rebalance the assembly. This was mentionned in another post if you bought the mass rebuilder shortblock. You can internally balance it, which is better in terms of performance, smoothness and longevity, but more expensive. Or, you can have it balanced externally which is stock and use the B&M flexplate.
 
I am not an professional engine builder like moper so listen to him but why must you rebalance if the pistons weigh the same or within a few grams? I think everyone assumed theres a big weight difference in the pistons which may not be true.
 
I'm stoked with all the cool feedback!

Print out of the weights is a superb idea.

Old pistons are probably history by now. I will look into it though.

The weight of the new pistons I do believe are lighter as the new ones are aluminum.

What "pads" are you talking about.....Are you saying that the motor may be able to be balanced by removing mateial off of the crank rather than adding weight? Is this still an externally balanced application with the balance method mentioned?

Trying still to better understand......Thanks for all the help I'm getting.
For me this is priceless.

Thanks from Modesto!
 
lighter pistons mean they can just drill the crank which is cheaper than adding metal. pads are on ends of rods so you lighten bob weight(recriprocating weight)if pistons were heavier. if you drill the crank its still internal balance.
 
You have to remember the weights we are talking about in terms of imbalance are in grams. If you replaced stock pistons the new ones will be lighter. The factory cast pistons have expansion limiters (steel bars) in them and they are heavy. The performance replacements are lighter by a bit usually. You could run with the crank a little heavy. It's called "overbalanced" and it is used to help some engines with shift recovery and throttle response in circle track builds. But really the only way I'd run without balancing is without replacing pistons. Factory balance jobs can be as far as 20g out. So if you can get weights for both and they are less than say, 10-15 grams, you might get away with it. I wouldnt advise it. But it might work.
 
FYI, when I built my 360 I used KB107 pistons and Eagle SIR rods both are lighter than stock. When I had it balanced they removed 200 grams from one end of the crank and 240 from the other end, that is almost a pound of metal. Can't imagine how that sucker would have vibrated at even 2000 rpm.

Spend the $200 to have it balanced.

In hind site I could have easily had my engine internally balanced with that amount of weight being removed for the external balance.
 
dgc333 said:
FYI, when I built my 360 I used KB107 pistons and Eagle SIR rods both are lighter than stock. When I had it balanced they removed 200 grams from one end of the crank and 240 from the other end, that is almost a pound of metal. Can't imagine how that sucker would have vibrated at even 2000 rpm.

Spend the $200 to have it balanced.

In hind site I could have easily had my engine internally balanced with that amount of weight being removed for the external balance.
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Hey I got a stock 360 crank with h beam rods and weisco forged pistons. I haven’t got a balancer or flex plate yet, do you recommend getting neutral? I’m new to this too. I plan on running it at the track mostly.
 
Woodall102093 said:
Hey I got a stock 360 crank with h beam rods and weisco forged pistons. I haven’t got a balancer or flex plate yet, do you recommend getting neutral? I’m new to this too. I plan on running it at the track mostly.
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The stock 360 was externally balanced, so no I wouldn't recommend it unless you get it balanced internally. You should get it balanced since you've changed pistons and rods.
 
daredevil said:
I am not an professional engine builder like moper so listen to him but why must you rebalance if the pistons weigh the same or within a few grams? I think everyone assumed theres a big weight difference in the pistons which may not be true.
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Between trw old style pistons and new aftermarket , there is a whole bunch of diiff. in weight . If so , I`d rebalance , if really close , I`d go with them on a street car.
 
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