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Crankshaft balance by manuf, how accurate?

General engine tech -- Drag Racing to Circle Track

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Bwh998
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Crankshaft balance by manuf, how accurate?

Post by Bwh998 » Fri Jul 31, 2020 7:43 am

How accurate are the balance jobs done by the manufacturers? Looking at Lunati and Crower mostly. Internal balanced small block chev, somewhere around 3.6 stroke. Assuming I supply them with the correct bob weight and get everything right on my end, they should be good to go, right?

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Re: Crankshaft balance by manuf, how accurate?

Post by Walter R. Malik » Fri Jul 31, 2020 9:55 am

Bwh998 wrote:
Fri Jul 31, 2020 7:43 am
How accurate are the balance jobs done by the manufacturers? Looking at Lunati and Crower mostly. Internal balanced small block chev, somewhere around 3.6 stroke. Assuming I supply them with the correct bob weight and get everything right on my end, they should be good to go, right?
Call them ... they will probably freely tell you the limits of their balancing.
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Re: Crankshaft balance by manuf, how accurate?

Post by BillK » Fri Jul 31, 2020 11:07 am

Dont know about Lunati and Crower but I have checked a couple of Eagle ones in the past and they have been pretty much done properly.
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Dave Koehler
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Re: Crankshaft balance by manuf, how accurate?

Post by Dave Koehler » Fri Jul 31, 2020 4:07 pm

Where I see problems is companies selling low bidder / budget type "balanced" assemblies.
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Re: Crankshaft balance by manuf, how accurate?

Post by Bwh998 » Fri Jul 31, 2020 6:33 pm

Dave Koehler wrote:
Fri Jul 31, 2020 4:07 pm
Where I see problems is companies selling low bidder / budget type "balanced" assemblies.
I see you offer no holes balancing, thats what I'm looking for. I've never done one before, can you just balance the crank to my bob weight and then trust that the flexplate and harmonic damper are both neutral balanced? Or does that all need to be balanced as an assembly for best results?

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Re: Crankshaft balance by manuf, how accurate?

Post by lefty o » Fri Jul 31, 2020 7:23 pm

i would never trust something from a manufacturer or some big name engine builder/parts seller. ive seen balanced rotating assemblies sold by fairly big names that are lucky to be ball park weight matched, much less actually balanced. you are at the mercy of someones employee doing a good job on your part. IMO best to be double checked at a minimum by your favorite trusted engine builder/machinist.

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Re: Crankshaft balance by manuf, how accurate?

Post by Dave Koehler » Fri Jul 31, 2020 7:52 pm

Bwh998 wrote:
Fri Jul 31, 2020 6:33 pm
Dave Koehler wrote:
Fri Jul 31, 2020 4:07 pm
Where I see problems is companies selling low bidder / budget type "balanced" assemblies.
I see you offer no holes balancing, thats what I'm looking for. I've never done one before, can you just balance the crank to my bob weight and then trust that the flexplate and harmonic damper are both neutral balanced? Or does that all need to be balanced as an assembly for best results?
The answer is yes.
I would have the flexplate checked and zeroed though.
Even the expensive ones can be goofy. Center welded cockeyed from the ring gear, etc.
Aftermarket neutral dampners like ATI have not been a problem out of the box.
Someone is bound to say it must be done all at once. Ehhh, no.
The difference with and without on a neutral deal is the flea on the elephant scenario.

IF you buy from one of the American Crank makers you can likely have the no hole done at that time. Kind of a win/win time wise.
Go cheap and doing this after the fact could run into some serious coin.
Likely you will come out with the same or more money than the mfg can provide at mfg time.
Just sayin' 8)
Like you intend, have your bobweight all figured out.
I will say to be prepared to give the mfg all the weights, not just the total.
They or I will want to be sure your numbers make sense.

I will also say unless you buy top of the line pistons and rods don't assume the weights on the box are dead on and that all the parts weigh the same.
Even then check everything.
It will surprise you.
Stuff happens.
Trust but verify.
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Re: Crankshaft balance by manuf, how accurate?

Post by Bwh998 » Fri Jul 31, 2020 8:02 pm

Thank you. Exactly what I needed to know.

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Re: Crankshaft balance by manuf, how accurate?

Post by needforspeed66gt » Sat Aug 01, 2020 3:05 pm

lefty o wrote:
Fri Jul 31, 2020 7:23 pm
i would never trust something from a manufacturer or some big name engine builder/parts seller. ive seen balanced rotating assemblies sold by fairly big names that are lucky to be ball park weight matched, much less actually balanced. you are at the mercy of someones employee doing a good job on your part. IMO best to be double checked at a minimum by your favorite trusted engine builder/machinist.
This.

When you buy a $2500+ crank, they usually lathe turn balance them at the manufacturer like I do all my cranks....problem is that I see them slightly "in tolerance" but the imbalance point is sometimes rotated off the counterweight completely making me need to add weight to the opposite end to pull it back out of an under-balance situation. Didn't check a Crower crank myself years ago after they assured me it was balanced and it had a vibration, don't trust them.
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