383 piston change ones again

[1970lynch]

Hey everyone. I have read few threads on this subj but feels like non of them are the same as mine if not please guide me. Thanks.
So i have 2468130-2 number 383 block. It has stock pistons, rods, crank when i bought it. As cylinders needed to be bored i had to change pistons to .030 over. I have bought KB-400 pistons.
According to other threads stock piston for 383 block weight 770 grams. According to UEM site KB-400 weights 766 grams.
The question is: do i have to make a rotating assembly balance with new pistons (everything else from rotating assembly stays the same) or this weight difference is not that critical?

 

[33 IMP]

I think (very willing to be proved wrong!) that four grams is under factory balance tolerance. I think i remember 10 grams + or - was acceptable .
I wouldnt worry at all. I WOULD weigh the old pistons, to make sure your info is correct.

 

[oldkimmer]

My last engine build on a factory 340 the lightest rod was 732 grams and the heaviest was 748 grams. Apparently the factory thought it was good enough. The pistons were also a few grams off from each other. Weigh ur rods and see if u can mix and match weight pairs. All pistons never seem to weigh the same. Kim

 

[steve340]

If your weights are right you would probably get away without balancing.
An engine can be surprisingly tolerant to imbalances inside the crankcase.
However I would recommend you get a reputable shop to do it because it can highlight other issues that may cause problems.
EG - wrong or wobbly harmonic damper or incorrect flex plate etc.
My view is for around $400 I know it is going to run right- provided it is done right.
If the budget is tight that will be a factor.
In your post you say you bought this engine you cannot be sure how it ran or whether the components truly matched.

 

[dvw]

Light piston won't hurt anything. Its reciprocating weight. You are fine.
Doug

 

[1 Wild R/T]

As I've pointed out many times how much do you think the oil that gets caught up in the windage from the crankshaft weights? Do you think it's evenly distributed?

 

[1970lynch]

If your weights are right you would probably get away without balancing.
An engine can be surprisingly tolerant to imbalances inside the crankcase.
However I would recommend you get a reputable shop to do it because it can highlight other issues that may cause problems.
EG - wrong or wobbly harmonic damper or incorrect flex plate etc.
My view is for around $400 I know it is going to run right- provided it is done right.
If the budget is tight that will be a factor.
In your post you say you bought this engine you cannot be sure how it ran or whether the components truly matched.

I would like to make it with no hesitation, the problem is that there is no proper machine shop here in russia. Especially in saint petersburg where i am located.

Thanks for all the answers. I should start with weight in all of the rods, old pistons and new pistons to see the real weights and move from there.

 

[jeepthrills01]

I would like to make it with no hesitation, the problem is that there is no proper machine shop here in russia. Especially in saint petersburg where i am located.

Thanks for all the answers. I should start with weight in all of the rods, old pistons and new pistons to see the real weights and move from there.

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