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What are your balancing tolerances?
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RCP Phx
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PostPosted: Sat Jun 25, 2022 8:52 am    Post subject: What are your balancing tolerances? Reply with quote

Putting together another stroker and I'm curious what you all accept/expect for tolerances?
BTW, I'm dealing with a Scat crank, Scat rods, and Racetec pistons.
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58ragman
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PostPosted: Sat Jun 25, 2022 12:27 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

.2 tenths of a gram
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58ragman
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PostPosted: Sat Jun 25, 2022 12:28 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

so say rods are 471.6 grams the close rod would be like 471.4 grams thats is how close it needs to be if your paying the doe.

it would only be 4 rods so it is possible.

its done all the time on american V8 shit same with pistons rings pins etc
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RCP Phx
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PostPosted: Sat Jun 25, 2022 3:37 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

That's kind of my dilemma, I built this same motor 2 yrs ago for me. I managed to get a combination of the parts to achieve .25grams difference between the combo's. This time I can only get to 2.3 grams at best do to the rods having a 3.2 gram difference in weight. They are end weight matched directly from Scat!
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58ragman
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PostPosted: Sat Jun 25, 2022 6:10 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

yeah the current rods i heard are all over the place with tolerances but find the lightest and match them all to that one. rods are balanced to each other and also end for end kind of tricky
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RCP Phx
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PostPosted: Sat Jun 25, 2022 6:33 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

I don't have the equipment to end balance rods and it's not my motor that's why I asked about general acceptable tolerances since this is not a high rpm/ high HP motor build.
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modok
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PostPosted: Sat Jun 25, 2022 7:06 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

1% weight difference is limit for stock
0.5% for HIGH performance

you can go down to a tenth of a percent but I don't believe it has any REAL benefit.
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PostPosted: Sat Jun 25, 2022 7:37 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

I have a set of these that are about 2 tenths out of the box, really good workmanship

https://www.cbperformance.com/product-p/1289.htm
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RCP Phx
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PostPosted: Sat Jun 25, 2022 8:36 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

I would love to get more input on this before I make any recommendations but the assembly would definitely comply with the 0.5% rule.
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PostPosted: Sun Jun 26, 2022 3:50 am    Post subject: Re: What are your balancing tolerances? Reply with quote

I take my time and balance everything to 0 ,,,,yep zero Wink Perfect Cool
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PostPosted: Sun Jun 26, 2022 8:22 am    Post subject: Re: What are your balancing tolerances? Reply with quote

Again I'm just donating my time for the build as a favor to Russ at Bishop-Buehl in California. The client I have only met twice but it is definitely his call! I'm only in the pre-preassembly stages right now checking all the parts and weights!
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modok
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PostPosted: Sun Jun 26, 2022 10:52 am    Post subject: Re: What are your balancing tolerances? Reply with quote

Sorry for the mixed messages, bit confusing.

I could make some alternate accounts and argue with myself Rolling Eyes ,
Never have but think about it more and more.
That would help to kind of BRING OUT a lot more perspective, from, lets say all the interesting characters I learned from in the past, because, well, they can't bring themselves back to life.

If you are balancing the rods and pistons to 2x the tolerance of what the crank is balanced to then your probably wasting your time on the wrong part or just in general.
Balancing the whole crank and flywheel assembly down to one gram at the stroke diameter is rather hard to do repeatedly.

Scats rods USUALLY are matched to 1.5 grams difference total weight in a set but I don't think that is a guarantee it's just what they typically manage these days.
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PostPosted: Sun Jun 26, 2022 9:31 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

I went ahead and did the wrist pins and the pistons, they are now +/- .01 grams!
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PostPosted: Mon Jun 27, 2022 1:11 am    Post subject: Re: What are your balancing tolerances? Reply with quote

1/3 ounce inches was as good as older crank balancing machines could do.
So that's about 6 grams at a 3" stroke

More modern machinery CAN go to half that, not always practical. You can be chasing ghosts of low spots around oil holes or vibration in the belt drive....only if everything is running totally SMOOTH will it be real.

Raby is going with 0.2 ounce inches these days, so he says.
And rods within 0.5 grams
https://aircooledtechnology.com/dynamic-balancing/

You want to balance the rods? Just need some skateboard wheel bearings, bit of sheetmetal and some string. maybe 2 hour project.
Some of the setup tools may look intimidating, but the key is to support the rod at the exact centers of the two bores.......which isn't THAT hard to do.
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PostPosted: Mon Jun 27, 2022 7:19 am    Post subject: Re: What are your balancing tolerances? Reply with quote

madmike wrote:
I take my time and balance everything to 0 ,,,,yep zero Wink Perfect Cool


Yup. The shop I worked at in the '70s had a digital dope scale. 1/100 of a gram Cool
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RCP Phx
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PostPosted: Mon Jun 27, 2022 8:02 am    Post subject: Re: What are your balancing tolerances? Reply with quote

I wouldn't hesitate a second on buying a good rod balancing jig except for the fact I would still have to send out the cranks to get balanced!
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PostPosted: Mon Jun 27, 2022 3:43 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

I have been meaning to machine some rod/rig for balancing. But I am just not in mood to go in the garage.

For street use - half-gram is plenty...on rods and pistons.

For race use - 1/tenth gram is the usual on rods and pistons.

The crank/flywheel/pressure plt/ pulley - balance them down to the lowest tolerance you can afford. this be - 0.2 ounce inch tolerance good for 9500 RPM.

YOu nee a dynamic balancer for the rotating parts.

I just set a friend of mine in TX - a Stewart Warner 2000 dynamic balancer. Not sure if he is taking work right now.

I can do the balance job if you care to send this way.
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PostPosted: Mon Jun 27, 2022 4:47 pm    Post subject: Re: What are your balancing tolerances? Reply with quote

I picked up a nice digital type scale that was repeatably accurate to within .1 grams, so I just matched all parts for weight when I did my rods and pistons, easy but time consuming. I'm happy with the extra work when added to the fact that just in mocking up alone I took the engine apart a dozen times. What's another hour? I'm not getting paid by the hour and I'm not likely to ever build an engine more than once every few years.
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PostPosted: Thu Jun 30, 2022 9:54 am    Post subject: Re: What are your balancing tolerances? Reply with quote

mike is correct. why would you waste &$ time almost balancing something?
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PostPosted: Sat Jul 02, 2022 5:04 am    Post subject: Re: What are your balancing tolerances? Reply with quote

That is like saying why need a .50 cal when you can kill it w/ .22

If you want to vaporize it— need more.
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