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Old 11-08-2008, 06:35 PM
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crankshaft balancing

I have gotten back a crankshaft from a machine shop. I have a funny feeling that the guy that sent out the crankshaft had it neutral balanced. Does anyone happen to know if I would have any long term problem with the crank shaft ,being neutral balanced compared to having it balanced with the harmonic and fry wheel? Or does it just seem to run a little rougher than it normally would? I understand the real proper way of balancing it is with the harmonic and flywheel. The only reason I'm questioning this is because I still had in my possession the harmonic and flywheel.

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Last edited by Cutless442; 11-08-2008 at 09:29 PM. Reason: sorry got called away
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Old 11-08-2008, 09:01 PM
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442

I vaguely remember we were discussing somthing prior to this thread . I know your new here so try to be more specific & give lots of details OK?

You do know you can keep adding on indefinitely to your prior thread?

So whet the hell were we talking about?

Oh yea ..Us old times suffer from CRS can't remember $****!




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Old 11-08-2008, 10:02 PM
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I know a few guys will probably disagree with this but here goes anyway.

I'd rather have a crankshaft balanced with nothing attached to it at all. Use a good damper and have the flywheel balanced independently, if it needs it at all. Balancing a crank with a damper and flywheel installed ties the crank to those two components pretty much for good.

Now on to the more controversial part.

I have not ever seen a benefit to further balancing a crankshaft on an engine that was within factory tolerances. If you replace a component with something that has a significant weight difference, plus or minus, then a balance job is in order. Otherwise it's a waste of money, in my opinion.

I have a 496" big block that makes near 800hp and is shifted at 7400 rpm, and has done so for three years now. Cast 4.25" Eagle crank, Eagle H-Beam rods and Wiseco pistons with a 48cc dome. No balancing was done and it's rigidly mounted in the chassis. If the obvious imbalance was a factor then I'd feel it, see it on the bearings when it gets freshened up each winter, and the damper would have submitted by now. But none of this has happened.

I'm certain that in my case I could pick up 5 or maybe 10hp with a balance job but I can think of better ways to spend $200-250.

My point is, to the original poster, don't sweat it. your engine will be fine.



Larry


PS,

I should note for the newbies that every new crankshaft should be checked to see if it is within spec. I don't want anybody to make a huge screw up and then blame it on me.

Last edited by coldknock; 11-09-2008 at 11:19 AM. Reason: Covering my butt.
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Old 11-09-2008, 07:52 AM
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Thanks! This makes me feel better. I was worried that after a while of the engine getting some use, that I would have to rip it apart again because the barrings spun or some other type of problem arising from vibrations from the crank.
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Old 11-09-2008, 08:37 AM
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Internal or "neutral balance" as you call is is the preferred way to balance a performance crankshaft.

External balancing has an imbalance on each end that corrects the whole shaft. Once the crank begins to spin at high RPM, the corrections made on the balancer and flywheel begin to work against one another in a sense, creating more harmonic stress in the crankshaft.

The preferred way to balance a crank is to internally balance it by either adding or removing material on the counterweights.

If you install an aftermarket crank in an engine without balancing it, you are just gambling.

Unless you are using a reground factory crank that was made to run within a stock bobweight, you should have the assembly balanced, particularly when you are using lighter pistons, longer rods, stroker cranks, etc.

If the crank falls within an acceptable range of the bobweight, then it will have no appreciable noticeable imbalance and there will be no real horsepower loss or gain.


I've had some of the aftermarket stock cast steel stroker 383 cranks almost jump out of the cradle of the balancer they were so far off.
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Old 11-09-2008, 10:22 AM
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Sometimes ya get lucky with a assembly, sometimes ya don't.

I just balanced a 440 OEM Chrysler that had 22 grams different, low-to-high on the big ends of the rods alone. The crank was also different 45 grams from end-to-end.

Then there was the 350 that was 40 grams light on the counterweight from the factory........

tom
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Old 11-09-2008, 11:22 AM
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Quote:
Originally Posted by machine shop tom
Sometimes ya get lucky with a assembly, sometimes ya don't.

I just balanced a 440 OEM Chrysler that had 22 grams different, low-to-high on the big ends of the rods alone. The crank was also different 45 grams from end-to-end.

Then there was the 350 that was 40 grams light on the counterweight from the factory........

tom

I edited my original post after I thought about how many people are gonna read it. Some folks really will put grease on their brakes to stop the noise........



Larry
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Old 11-09-2008, 12:34 PM
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Quote:
Originally Posted by NAIRB
I've had some of the aftermarket stock cast steel stroker 383 cranks almost jump out of the cradle of the balancer they were so far off.

That has happened to me before, as well............scared the hell outta me, the first time it happened.....
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