Basic Magnum Engine question

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KevinB

KevinB

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Building my 5.9...and so far have the short block together except for decreeing the cam. My question is about balancing, a subject I know little about.

So the magnum is externally balanced. This means both the flywheel and harmonic balancer contribute to the overall balancing of the assembly, correct?

My engine is a fresh rebuild with a reground, repolished crank, new pistons and bearings, etc. Also may machinist marked each piston and rod assembly as to what cylinder it should be in...I assume for balancing them.

My Question then is this: Do I need to take my short block to an engine shop to have it further balanced, with the weighted flywheel and balancer attached? Sorry for the basic question...it's my first time putting an engine together.


Edit: I should mention the pistons are supposed to be factory replacement .02 over. Just talked to the machinist and he said he did not do a dynamic balancing on it but feel 99% confident it wouldn't need that based on the factory replacement pistons. Maybe its work double checking the piston weight vs factory to make sure it's on the money?
 
Lelo Dart said:
My 20 over speed pros were way heavier than the stock pistons and motor needed to be balanced.
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There's no data available for my sealed power Pistons. I have a note in with fed mogul to find out...the stock magnum pistons are 470g and aluminum. I'm hoping the sealed power are close.
 
Without the actual wieght of the old pistons you are just guessing, weight also includes the rings.
The KB 107's is used in my mag were lighter so mallory needed to be added to the crank.
 
sireland67 said:
Without the actual wieght of the old pistons you are just guessing, weight also includes the rings.
The KB 107's is used in my mag were lighter so mallory needed to be added to the crank.
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Id be surprised if there was enough of a difference between the old and new rings to matter, but maybe that's true. I have the listed weight of the old pistons, according to Larry Shepard anyway. Is that not a good enough go by?
 
Lelo Dart said:
I thought speed pro and sealed power were the same thing? Lightening bolt on the skirt?
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Yes I think they are the same? Your reply was unclear as to if you have a magnum, and if you have stock compression pistons. Mine are part number: h655cp50mm
 
Yes to both questions, tried to dig up a part # but it's been a few years. My machinist also thought they should be about the same (stock replacements) but I wanted it balanced anyway, then he said good thing because they were quite a bit heavier and would have caused problems.
 
Lelo Dart said:
Yes to both questions, tried to dig up a part # but it's been a few years. My machinist also thought they should be about the same (stock replacements) but I wanted it balanced anyway, then he said good thing because they were quite a bit heavier and would have caused problems.
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Hmm well I'll definitely find out about the weight one way or another. Thanks for the heads up!
 
If the machinist swapped pistons, he probably weighted old and new to determine they are super close.

You said you got .002" over pistons or do you mean .020" over? One would require boring cylinders to 4.020" and .002" would be a ball hone.

Balancing an engine requires you to present all rotating parts to machinist at once, prior to assembly. This would be, pistons, rods, crank, damper and flex/fly.

Just call him in morning and ask, there are no stupid questions, only stupid answers.
 
magnummopar said:
If the machinist swapped pistons, he probably weighted old and new to determine they are super close.

You said you got .002" over pistons or do you mean .020" over? One would require boring cylinders to 4.020" and .002" would be a ball hone.

Balancing an engine requires you to present all rotating parts to machinist at once, prior to assembly. This would be, pistons, rods, crank, damper and flex/fly.

Just call him in morning and ask, there are no stupid questions, only stupid answers.
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Thanks, and I meant .020 over. This was a few months ago and I asked him today to what extent he balanced. He didn't clarify if he had matched piston weights old to new, just that he didn't do a rotate balance. He did have all of those pieces at the time. Oh well...we will see what sealed power says. A couple of sites list the piston at 1.37 lbs, but it looks like that includes the pin. If you subtract what Larry says the pin is supposed to weigh, you get 466.82g, which is 3.17g lighter than the supposed 470g quoted in Larrys book. That seems promising but...

At what point would the balancing need to be addressed? Is 3g too much to ignore? Or is that within tolerance?
 
I dont think 3g will be a problem, many times budget cast pistons are a gram or more different between heaviest and lightest in set, which is worse than 3g heavier than original ones.

You said they were factory replacement, are they hypereutectic or just regular cast?
 
Not like it may seem to matter- but all 360s including 5.9 Mags are external balance, 5.2 Mags are internal balance same as all other 318s.
 
magnummopar said:
I dont think 3g will be a problem, many times budget cast pistons are a gram or more different between heaviest and lightest in set, which is worse than 3g heavier than original ones.

You said they were factory replacement, are they hypereutectic or just regular cast?
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Hypereuxtectic. Or however it's spelled
 
Ok so I got off the phone with sealed power and got the info...this is good info for anyone to have that's rebuilding a magnum and going .020 over.

The Sealed Power piston, part number WH65550MM weighs 620 grams with the wrist pin. Subtract the factory wrist pin weight of 154.6 grams and you get 465.4 grams, or a difference of 4.6 grams lighter for the new piston when compared to the factory 470 gram slug. That should be within tolerance for not needing to rebalance, correct?
 
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