Should I balance the crank, or

[Dave Koehler]

Has anyone else noticed today's aftermarket pistons and rods come out of the box balanced, so often nothing beyond weighing for confirmation is required, but the cost of the balance job has gone up?

I respectfully disagree on that.
It is still a crap shoot.
If you have a scale that does not read in tenths or accept a looser tolerance then yes they are all perfect.
Once in a great while I will actually get a piston set like that but it is definitely not the norm.
Rods are the same way. The only time I get one of those perfect sets is with a set of billet aluminum rods or the high end rods.
Never with low bidder rods.

Capri. Quit screwing around. 90 grams (2.74 ounces) per throw difference? Come on. Do it right.

Or standard was 2.5 grams up or down, but we tried to keep them within 1 gram. A production run varied about 12 grams from lightest to heaviest. I had the luxury of productions runs, it's a lot harder it you're making 8.

But, you've got to admit, they are a lot closer than they were back when it was all manual machinery.

Agreed on that. I am tickled when I get a set that is within 2.5. That makes it very feasible to dial them in.

[BigBro74]

Heck , I was pricing getting a replacement crank spun up for a 406 I’m working on- the “target” bobweight on the crank is only 7 grams from the actual (and I would be okay with that) “if”measured) -but - there is the manufacturer “+-2%” unknown on that target which could really derail my plans -so going to pay up and feel better about it I guess- I know it is kind of a costly verification, but would likely be cheaper than a tear down when the engine vibrates.....
Opinion-no sarc- Jason

[Dave Koehler]

Heck , I was pricing getting a replacement crank spun up for a 406 I’m working on- the “target” bobweight on the crank is only 7 grams from the actual (and I would be okay with that) “if”measured) -but - there is the manufacturer “+-2%” unknown on that target which could really derail my plans -so going to pay up and feel better about it I guess- I know it is kind of a costly verification, but would likely be cheaper than a tear down when the engine vibrates.....
Opinion-no sarc- Jason

You were wise to do that. =-2% really means a 4% spread from light to heavy from their target number
Just because a mfg says that a crank can accept a certain weight of bobweight does not mean that it will in real time.
It could come up heavier which is fine or too light which can be financially annoying.

[Caprimaniac]

Got hold of a guy who can do this in a week.

In Our money, it's 700 NORMAL$. In Corona$, it's more like 510.... So, 700$ for balancing w/ flywheel, balancer & getting the parts weighed.

I'm goodf or weighing my stuff, and the balancer and flywheel are both neutral, so I'll get the price Down.

Still not convinced it will do ANYTHING for the engine. Unfortunately, I do not have the cash to build two identical engines to test; one With balanced, one With an unbalanced crank straight from the cardbox......

[Dave Koehler]

You don't seem convinced.
While not a proper comparison test please try this.
Go outside and hang 90 grams on one of your front rims of your daily driver.
Let me know what you think after driving for a little while.

[n2omike]

You don't seem convinced.
While not a proper comparison test please try this.
Go outside and hang 90 grams on one of your front rims of your daily driver.
Let me know what you think after driving for a little while.

EXACTLY! 90 grams is a LOT!
Get it balanced!

[Caprimaniac]

You don't seem convinced.
While not a proper comparison test please try this.
Go outside and hang 90 grams on one of your front rims of your daily driver.
Let me know what you think after driving for a little while.

That would give a very unpleasant drive, true. So, why haven’t my teeth been shaken to pieces as none previous cranks have been balanced? Pure luck, maybe.

However- pay the same as a new crankshaft to get it balanced? By two instead, test and pick the best?

However..... Have a question. The guy balancing the forged Eagle crank - no ESP or othe treatment on crank- claims that the steel is so hard that his bore bits brake????
(And ofcourse, it will take a couple of weeks for him to get new drills...)
Anyone seen this?

And BTW- he also said he had to remove 250g both front and rear- seems like much to me. Or normal?

Thanks
RS

[Dave Koehler]

You asked the question.
You got good answers from different sources.
You don't like the answers

so don't balance it.

It doesn't belong to any of us.
I and maybe we no longer care.

Hard? no. Wrong bits, wrong speed, wrong feed, etc,

[Dave Koehler]

I have reconsidered my answer on drilling cranks that are harder than most oem.

If your man is using cheap drill bits then yes anything over a cast crank and most oem cranks is going to seem hard.
If he primarily deals with oem cranks a 4340 crank may seem harder than the hinges of hell's gate.
So I pass this along for his consideration.
I have noted examples to go by. Buy them where you can.

A good step up from cheap drill bits is Cobalt drill bits.
More money, yes but that's tooling you need.
Downside is that eventually you will wear it down or worse chip it.
In that case you need spares while you send it off for sharpening.
Like this. https://www.mcmaster.com/8939a18

Final and best step is a spade drill.
Don't let the initial buy in cost freak you out. Ok, maybe a little.
These kick butt and will likely be the last bit you buy.
The inserts are changeable and come with various coatings.
Basic Spade Drill: https://www.mscdirect.com/product/details/04597712
These are machinable. If your machine cannot accept a 1" diameter you can cut the shank down in a lathe
Morse taper versions are also available but I will let you search that out.

Inserts for the above spade drill:
Cobalt: https://www.mscdirect.com/product/details/04597712
Carbide: for the really tough cranks. You will know it when it happens. https://www.mscdirect.com/product/details/08076515
Inserts are available in any desired material and coating.

Feeds: Start dead slow until you break through the skin of the surface. You will eventually find the sweet rpm spot for any crank.

Cutting Fluid: It won't hurt to use a little of your favorite cutting fluid.
I found this fluid to work well with minimal smoke. Request a sample.
https://unist.com/product.html?prod=2210ep
Their aluminum version also works with even less smoke.

[racear2865]

like has been told to you above in several places. 90 grams per bobweight is a lot of metal to sling out of balance. And you are correct, a 90 gram weight on a tire is a different world but not all that unreal. The only reason that you dont feel all the imbalance is that the crankshaft is captured in 5 main bearings. Therefore they will bear the brunt of the vibration. That imbalance will also pound the oil film from around the crank and expose the bearing to come in physical contact with the journal on the crank. And yes a 4340 crank is slightly more difficult to drill "if" you do not have the prop drill, as stated above, to remove the metal. You will pay now or pay later. Im really having a difficult time understanding your thought process. If you felt you needed to purchase a 4340 crankshaft, then why do you not feel it is worth it to do it correctly.
reed

[Caprimaniac]

Many thanks, Dave. You are a great source for such knowledge and I will pass on the information on to the machinist/ balancer guy.

Yes- I am aware of the bearing issue vs unbalanced crank, and that’s one of the reasons I spent the money.

Puzzling me is the claimed 250g to remove...

I think Eagle say 1750 +\- 5%? So max 1840g. And new bobweight ~650. Leaves 190g to remove.

Maybe Eagle are way more than the 5% off?

Bummer cos’ Easter would be perfect for assembling this motor... engine.... . Leave time for other hotrods and projects so I dont cry over waiting.

Happy easter holidays

[Dave Koehler]

I will just say that it doesn't work that way. Remember you have 4 bobweights contributing.

[BigBro74]

In my experience too —which is not even in the same league or anything to compare as Dave K’s ——scat cranks that I have gotten balanced have a LOT of extra weight to be removed ON purpose.
I don’t know about eagles - I have not used one YET -But I am about to find out when they send my crank -as theirs was more appropriate for the particular application- fingers crossed .... I sent them the weight and had them do it in house—like said fingers crossed.!
Jason

[Caprimaniac]

Yes, thank you. Undertood by looking at that thread on Scat crank balancing that Dave dug up.

Machinist is still struggling... Called med yesterday for an update (which gave no NEW information....). His drillbits are worn out- as he told me last week.