Crankshaft balance holes

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1972ho
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Crankshaft balance holes

Post by 1972ho » Mon Oct 16, 2017 5:49 pm

Just checked out my crank at the machine shop and because I have went with a lighter weight rod and piston assembly they had to bore 3 holes in the front counterweight,Question is how deep should the holes be when I went to take a look the holes are as deep as 3 to 4 inches, is this normal.Thanks

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Re: Crankshaft balance holes

Post by statsystems » Mon Oct 16, 2017 6:08 pm

1972ho wrote:
Mon Oct 16, 2017 5:49 pm
Just checked out my crank at the machine shop and because I have went with a lighter weight rod and piston assembly they had to bore 3 holes in the front counterweight,Question is how deep should the holes be when I went to take a look the holes are as deep as 3 to 4 inches, is this normal.Thanks
If the balance job is correct it doesn't matter how deep the holes are. You can't just look at a balance job and tell if it's right or wrong.

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Re: Crankshaft balance holes

Post by superpursuit » Mon Oct 16, 2017 6:37 pm

^^^^^^^^^
x2 on this. How much weight needed to be removed depends on how much lighter the bob weight is now.

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Re: Crankshaft balance holes

Post by Walter R. Malik » Tue Oct 17, 2017 9:41 am

1972ho wrote:
Mon Oct 16, 2017 5:49 pm
Just checked out my crank at the machine shop and because I have went with a lighter weight rod and piston assembly they had to bore 3 holes in the front counterweight,Question is how deep should the holes be when I went to take a look the holes are as deep as 3 to 4 inches, is this normal.Thanks
The balance holes should be no deeper than just below the plane of the main bearing surface.

In my opinion ... with that many holes that deep, (unless they are small diameter), they should have cut down the counterweights a little first because the radial balance can now suffer even though the rotational balance is smooth.
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Re: Crankshaft balance holes

Post by mag2555 » Tue Oct 17, 2017 10:27 am

X2 with Walter on this!

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Re: Crankshaft balance holes

Post by statsystems » Tue Oct 17, 2017 10:43 am

Walter R. Malik wrote:
Tue Oct 17, 2017 9:41 am
1972ho wrote:
Mon Oct 16, 2017 5:49 pm
Just checked out my crank at the machine shop and because I have went with a lighter weight rod and piston assembly they had to bore 3 holes in the front counterweight,Question is how deep should the holes be when I went to take a look the holes are as deep as 3 to 4 inches, is this normal.Thanks
The balance holes should be no deeper than just below the plane of the main bearing surface.

In my opinion ... with that many holes that deep, (unless they are small diameter), they should have cut down the counterweights a little first because the radial balance can now suffer even though the rotational balance is smooth.

This is correct but, BUT...I ignored has depth because that is a deep hole and I don't think I've ever seen holes that deep on the worst of the balance jobs I've seen.

As you remove the weight closer to the center it does less so Walter is correct. My issue is in 2017 I can't believe some would drill holes that deep,who,has done more than 2-3 balance jobs, or that shop would still be in business.

It's kind of like the guy who caught the 12 inch fish but it was really 4 inches. After 2 beers it was a 16 inch fish. Perception is not the same as a measurement.

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Re: Crankshaft balance holes

Post by 1972ho » Tue Oct 17, 2017 1:58 pm

The reason they said they could not machine the counterweights down was that they were not thick enough ,this is a moldex billet even fire crank if that makes a difference.

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Re: Crankshaft balance holes

Post by ProPower engines » Tue Oct 17, 2017 2:39 pm

1972ho wrote:
Tue Oct 17, 2017 1:58 pm
The reason they said they could not machine the counterweights down was that they were not thick enough ,this is a moldex billet even fire crank if that makes a difference.
Most if not all cranks we do are a no holes type balance and on more expensive cranks thats the only way to to it.
Machining a wide or narrow counter weight will not matter as long as the end result is the weight removed is what is needed to get the balance correct. If they choose to drill deep holes rather then turn the OD down sighting they were to narrow that may not have had a way to machine in far enough on their lathe :^o
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Re: Crankshaft balance holes

Post by Walter R. Malik » Wed Oct 18, 2017 12:10 am

ProPower engines wrote:
Tue Oct 17, 2017 2:39 pm
1972ho wrote:
Tue Oct 17, 2017 1:58 pm
The reason they said they could not machine the counterweights down was that they were not thick enough ,this is a moldex billet even fire crank if that makes a difference.
Most if not all cranks we do are a no holes type balance and on more expensive cranks thats the only way to to it.
Machining a wide or narrow counter weight will not matter as long as the end result is the weight removed is what is needed to get the balance correct. If they choose to drill deep holes rather then turn the OD down sighting they were to narrow that may not have had a way to machine in far enough on their lathe :^o
It is not easy to cam counterweights on a lathe but, sometimes they need to get "cammed" in order to remove enough weight without contacting the journal on the opposite side.
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Re: Crankshaft balance holes

Post by joe 90 » Wed Oct 18, 2017 12:53 am

I've trimmed counterweights on the crank grinding machine, set up on big ends.
Used the stone to trim them.

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Re: Crankshaft balance holes

Post by The Radius Kid » Wed Oct 18, 2017 1:02 am

1972ho wrote:
Tue Oct 17, 2017 1:58 pm
The reason they said they could not machine the counterweights down was that they were not thick enough ,this is a moldex billet even fire crank if that makes a difference.
They weren't thick enough to turn but they were thick enough to drill deep holes in?
Really?
I'd be real curious to see an explanation for that one.
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Re: Crankshaft balance holes

Post by MotionMachine » Wed Oct 18, 2017 8:06 am

The Radius Kid wrote:
Wed Oct 18, 2017 1:02 am
1972ho wrote:
Tue Oct 17, 2017 1:58 pm
The reason they said they could not machine the counterweights down was that they were not thick enough ,this is a moldex billet even fire crank if that makes a difference.
They weren't thick enough to turn but they were thick enough to drill deep holes in?
Really?
I'd be real curious to see an explanation for that one.
Like Joe said above, it can be done on a crank grinder, I've done several that way. It's a PITA because it's an interrupted cut (grind) but you just offset the stroke to match the original cam ground counterweight so you maximize weight removal in the correct spot. With indexing chucks it's easy to move on to the next one after the initial setup.

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Re: Crankshaft balance holes

Post by Walter R. Malik » Wed Oct 18, 2017 10:17 am

MotionMachine wrote:
Wed Oct 18, 2017 8:06 am

Like Joe said above, it can be done on a crank grinder, I've done several that way. It's a PITA because it's an interrupted cut (grind) but you just offset the stroke to match the original cam ground counterweight so you maximize weight removal in the correct spot. With indexing chucks it's easy to move on to the next one after the initial setup.
YEP ... but, a lot of shops who do balancing do not have a crank grinder and don't want to pay someone else to do it.

SO, you get what you get from them.

Although ugly, you could grind those middle weights by hand
or, also put the crank on a bridgeport and put flats in the right places.
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Re: Crankshaft balance holes

Post by 1972ho » Wed Oct 18, 2017 11:54 am

This what my even fire crank counterweights look before drill it even had a some tungsten in the counterweight But was not removed.
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Re: Crankshaft balance holes

Post by jac mac » Sat Oct 28, 2017 1:58 am

V6 cranks, one even fire, other odd fire, are they correct harmonic balancers for each application, might the extra deep drilling be to compensate for balancer?

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