another balance question

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donclark
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another balance question

Post by donclark »

New pistons came in 17 gr heavier @411 gr. with rings. The old pins weighed 106 gr @ 0.787 x 2.250 x 0.200, H13. There is an H13 DLC 0.180 wall tapered pin available that weighs 91 gr. Problem solved. My questions are: a) is this enough pin and b) is 17 grams even enough to be concerned about. Total bob weight is 1356 gr, max engine speed will be 9400.
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Re: another balance question

Post by dwilliams »

"Don't worry, be happy." The balance machine can pick up 17g, but it won't make any difference when running.

If you're concerned about the pins call the manufacturer and ask their tech guys.
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Re: another balance question

Post by mag2555 »

A lot of engineers state that even 25 grams of unbalance is not a issue, but this it at 7000 or so rpm, at 9400 I would want far better tolerance then 17!
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
BillK
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Re: another balance question

Post by BillK »

What engine is it ?
Bill Koustenis
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donclark
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Re: another balance question

Post by donclark »

SBF, 3.25 stroke
steve316
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Re: another balance question

Post by steve316 »

When Bill Jenkins was running Pro Stock with a SBC he would over balance @ 52%. I have over and under balanced 35g and more. It didn't run any better or any worse, also the bearings looked like new on tear down.
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Re: another balance question

Post by Roundybout »

My biggest concern would be going to a heavier piston and a thinner wall pin. The weights involved in how it will balance out is secondary. I’m assuming a drag race application and 9400 RPM is at the shift/stripe. I’d talk to the piston/pin manufacturer for some possible guidance. If the current piston and pin combo looks good it may be marginal with the new stuff especially with the forces Involved at that RPM. My hunch is you’ll be ok but skimping on the pin to save weight is my last resort unless there’s a comfortable safety margin there.
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Re: another balance question

Post by KnightEngines »

I put pistons that were 45g heavier in a motor without a rebalance.
It turns 8200rpm & looks mint on pull down.

Just run it, you'll never know the difference.
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Re: another balance question

Post by mag2555 »

My main concern would also be for the unneeded weight placing a greater load on the Rods.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
donclark
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Re: another balance question

Post by donclark »

KnightEngines wrote: Fri Nov 08, 2019 1:28 am I put pistons that were 45g heavier in a motor without a rebalance.
It turns 8200rpm & looks mint on pull down.

Just run it, you'll never know the difference.
This was also the opinion of the man that did the original balance. His shop serviced engines for several ARCA teams back in the day. If you compare with the total bobweight, it amounts to 1.2%
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Re: another balance question

Post by Old School »

mag2555 wrote: Fri Nov 08, 2019 7:05 am My main concern would also be for the unneeded weight placing a greater load on the Rods.
Would you define the " unneeded weight" in this application?
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Re: another balance question

Post by mag2555 »

Just talking in general since we strive for light weight to have a more rev happy motor.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
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