Balance...neutral.....over.....under..????

[CNC BLOCKS]

Had a circle track 602 crate engine that had a lot of vibration issues, finally broke a timing chain and the rep from GM showed up to take the engine apart from there Checked the balance on the crank and it was 40 to 44 grams under balanced.

Called Rick King and his reply was you can over balance 40 grams but never under balance 40 grams.

[sanfordandson]

I remember a post by Darin Morgan stating that the pro stock engines liked to be under balance at 45%. He claimed it showed gains on the track AND on the dyno. Dont know if they still do that or not.

[SchmidtMotorWorks]

Had a circle track 602 crate engine that had a lot of vibration issues, finally broke a timing chain and the rep from GM showed up to take the engine apart from there Checked the balance on the crank and it was 40 to 44 grams under balanced.

Called Rick King and his reply was you can over balance 40 grams but never under balance 40 grams.

It has nothing to do with simple under or over balance, it might have to do with counterweight distribution but you can have an infinite number of different counterweight designs and still balance to one single bob weight. So the BW alone tells you close to nothing.

Notice the King crank (linked from their web-site) shown below, how the end CWs are not symmetrical?
That is an indication that CWs 2 and 3 are improperly designed. Could be the forging they use doesn't have material where it is needed but the way CW #2 is lightened is making the problem worse. CW #3 should have the fan more opposite the pin.

[Baprace]

Had a circle track 602 crate engine that had a lot of vibration issues, finally broke a timing chain and the rep from GM showed up to take the engine apart from there Checked the balance on the crank and it was 40 to 44 grams under balanced.

Called Rick King and his reply was you can over balance 40 grams but never under balance 40 grams.

It has nothing to do with simple under or over balance, it might have to do with counterweight distribution but you can have an infinite number of different counterweight designs and still balance to one single bob weight. So the BW alone tells you close to nothing.

Notice the King crank (linked from their web-site) shown below, how the end CWs are not symmetrical?
That is an indication that CWs 2 and 3 are improperly designed. Could be the forging they use doesn't have material where it is needed but the way CW #2 is lightened is making the problem worse. CW #3 should have the fan more opposite the pin.

Jon not for nothing but every answer you have is the counterweight is in the wrong location and you hate any balance issues or percentages that does not reflect your personal thoughts, you said you designed crankshafts for MAJOR manufacturers yet you still say the counterweights are in the wrong position, why didn't they/major manufacturers follow your thought process if you are correct and they are wrong ? Now just to stir the pot , I personaly think if you balance a blown engine at 50% it is automaticaly overbalanced to a degree because the engine never see's the full piston weight because of constant boost pressure trying to blow the piston into the pan. Just got done doing a Triumph mc crank for racing at 72% based on info from an old timer that raced at Daytona back in the day. Now one more thought in my head about Pro Stock being balanced at 45% perhaps they have figured out that they have a positive pressure on top of the piston and the actual piston weight is less than what the crankshaft actualy see's, they could be correct Now Carls fix on the crate engine is correct in my thought process because his pistons are sucking on the carb and the crank see's/feels a heavier piston. JMHO

PS: not trying to argue but either come up with a viable solution or ...............

[SchmidtMotorWorks]

Jon not for nothing but every answer you have is the counterweight is in the wrong location and you hate any balance issues or percentages that does not reflect your personal thoughts, you said you designed crankshafts for MAJOR manufacturers yet you still say the counterweights are in the wrong position, why didn't they/major manufacturers follow your thought process if you are correct and they are wrong ? Now just to stir the pot , I personaly think if you balance a blown engine at 50% it is automaticaly overbalanced to a degree because the engine never see's the full piston weight because of constant boost pressure trying to blow the piston into the pan. Just got done doing a Triumph mc crank for racing at 72% based on info from an old timer that raced at Daytona back in the day.

PS: not trying to argue but either come up with a viable solution or ..............

You start off with some incorrect assumptions.

1st: Cylinder pressure should not be involved in BW specs at all.

2nd, there are lots of cranks I like the design of, most crank design that are currently competitive running with 2.0 mains are good. Also most of the current nitro stuff is good, the old stuff was horrible.

The crank below is a much better design, notice how the CWs are more opposite of the rod pins and the end CWs are nearly symmetrical to the end rod pins.

The reason OEM crankshafts don't have the optimum CW design for racing engines is they have different criteria. A CW design that is correct for a production engine is different than that of a racing engine.

One of the main reasons racing cranks are billet is that you can't forge the material into the required shape for a racing engine counter weight layout cost effectively, it is possible, but the dies wear out very fast with the deep draws and with the die taper, it leaves lots of material to machine off, so the cost is unacceptable for a production engine.

[SchmidtMotorWorks]

Here is another good one.

[SchmidtMotorWorks]

Here is a terrible one

[SchmidtMotorWorks]

Here is an example of the old style of Nitro cranks used in the late 80s to early 90's. This was the design style used by Moldex, Crower, Black, BRC (IIRC).
They were designed to be easy and cheap to balance to any BW but they were hell on bearing loads and obviously very heavy IIRC about 90 lbs.

[SchmidtMotorWorks]

Now one more thought in my head about Pro Stock being balanced at 45% perhaps they have figured out that they have a positive pressure on top of the piston and the actual piston weight is less than what the crankshaft actualy see's, they could be correct Now Carls fix on the crate engine is correct in my thought process because his pistons are sucking on the carb and the crank see's/feels a heavier piston. JMHO

It isn't that complicated, they just lighten the BW as far as they can to get the crank lighter until the vibration causes other problems that or more important than having a lighter crank.

[SchmidtMotorWorks]

Here is what a more modern large crank looks like, again, notice the symmetry.

[Warp Speed]

Pretty much the way it is!

[Cubic_Cleveland]

Here is an example of the old style of Nitro cranks used in the late 80s to early 90's. This was the design style used by Moldex, Crower, Black, BRC (IIRC).
They were designed to be easy and cheap to balance to any BW but they were hell on bearing loads and obviously very heavy IIRC about 90 lbs.

image.jpg

Is the reason this crank isn't optimal because the counterweights for the 3/4 & 5/6 rods are so 'large' in area, and at 90* to the throw?

[SchmidtMotorWorks]

Is the reason this crank isn't optimal because the counterweights for the 3/4 & 5/6 rods are so 'large' in area, and at 90* to the throw?

Mostly, since CWs 2 and 3 are adjacent to the same main, they can be partially averaged toward each-other, in doing so they become more effective. For some engines with light parts, it is possible to make CWs 2 & 3 the optimum size but on most engines there isn't enough space to make 2 & 3 the desired mass.

Also, the idea of designing the CWs as though the engine were 4 V-twins is an over-simplification that doesn't work-out the way it intuitively seems like it would.

[Ron Clevenger]

Lot's of thoughts there to ponder for sure.

Maybe I missed it in the dialog, but I still have no clear understanding why or what for you would balance neutral or 52% over?? What are the different effects between the two?

Blessings............Ron

[brandonu]

http://www.circletrack.com/enginetech/c ... ewall.html

Maybe try the link above. It could help explain over/under balance.