Question about internally balanced engines

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Sep 4, 2002 | 12:49 PM

Old Blue Crew

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Question about internally balanced engines

As I'm building the bottom end of my 390, I got to thinking about all of the things that could affect all of the roatating masses: crank ground down, new rod bolts, new pistons.

What measures need to be taken to ensure that an internally balanced engine remains balanced after being rebuilt? Thanks for any help you can offer.

Bill

Sep 4, 2002 | 02:12 PM

Ratsmoker

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From: Missouri

Question about internally balanced engines

The pistons should be weighed so that they all weigh exactly the same. The same should be done with the rods. The crank should be ground the minimum amount needed on the journals and then balanced by the machine shop.

Sep 4, 2002 | 02:55 PM

Old Blue Crew

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Question about internally balanced engines

Thanks for the info ratsmoker. Am I correct in assuming that if I'm replacing my original pistons with lighter aluminum ones that everything's OK as long as they all weigh the same?

Sep 4, 2002 | 04:16 PM

canzus

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Question about internally balanced engines

No, it'll still need balancing, as the
weight has changed...

Steve & the Rockette
'63 F100
'68 F100
'72 Capri 2L
'73 Capri 2.6L V6
'73 MG B GT 2.6L V6(Ford)
'98 Contour SVT 2.5L V6, That blowed up real good...
'01 ZX2 (No Mods yet)

Sep 4, 2002 | 04:47 PM

Old Blue Crew

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Question about internally balanced engines

>No, it'll still need balancing, as the
>weight has changed...
>
>Steve & the Rockette
>'63 F100
>'68 F100
>'72 Capri 2L
>'73 Capri 2.6L V6
>'73 MG B GT 2.6L V6(Ford)
>'98 Contour SVT 2.5L V6, That blowed up real good...
>'01 ZX2 (No Mods yet)

You're referring to the crankshaft? I probably wasn't real clear...If I have my crankshaft balanced, do I need to be concerned about my pistons being lighter/heaver than the original ones?

Sep 4, 2002 | 10:23 PM

54_5star

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Question about internally balanced engines

That's all taken into account at the time of the balance job. You can do anything you want to the crank and rods before it's balanced just don't go grinding on stuff after that.

Sep 4, 2002 | 10:52 PM

Ratsmoker

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From: Missouri

Question about internally balanced engines

No, once the crank is balanced it is balanced. The pistons and rods are weighed individually. Their weight does not matter as long as all the rods weight the same and all the pistons weigh the same. They start by finding the lightest rod and piston and shaving the rest down to that weight.