440 crank

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oldkimmer

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Has anyone tried to lighten the stock crank before balancing? My new pistons and rods are 251 grams lighter per cylinder. Would I be better off to get a lighter aftermarket crank? Thanks. Kim
 
I'd think about cutting the counter weights down. When I built the 451 stroker with a factory 440 steel crank, I cut the counter weights .120" in radius for use with 6.76" H-beam rods and Ross forged flat top pistons. Took very little drilling on the crank after that to balance it.

My pistons were 510 gms and the pins were 158 gms. Scat H-beam rods for 2.375 journal.

Ask those that are going to do the balancing for you.
 
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IQ52 said:
I'd think about cutting the counter weights down. When I built the 451 stroker with a factory 440 steel crank, I cut the counter weights .120" in radius for use with 6.76" H-beam rods and Ross forged flat top pistons. Took very little drilling on the crank after that to balance it.

My pistons were 510 gms and the pins were 158 gms. Scat H-beam rods for 2.375 journal.

Ask those that are going to do the balancing for you.
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If I were going to cut on the counter weights, I`d knife edge the heck out of it .
 
I did both turning the CW's on a lathe, and radius/knife edge with a grinder. For a low deck, you need to turn the CW to clear the crankcase most times.

As long as it's "a remove", and that's normal for lighter parts, it's not a big deal. It's when you have to add heavy metal, such as going away from an aluminum rod motor, that it gets expensive. S/F....Ken M
 
oldkimmer said:
Has anyone tried to lighten the stock crank before balancing? My new pistons and rods are 251 grams lighter per cylinder. Would I be better off to get a lighter aftermarket crank? Thanks. Kim
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If you have access to a big lathe it is fairly easy to cut down the counterweights. Calculate how much bobweight needs to come off and then convert that to cubic inches of steel and you'll know how much depth to take off. We cut the counterweights down at the shop when we have to take off a lot of weight since drilling big holes in the crank is a bad idea. Once you know how to do it the task goes pretty quickly. If you do the calculation correctly you can often hit the balance number very closely so the final balancing only requires a dimple or two.
lathe.jpg
 
Thanks guys. I have the b4 weight for the pistons, pins and rods. So to figure bob weight I would times 251 by 8. Then how do I find the cubic inches of steel? Thanks. Kim
 
AndyF said:
If you have access to a big lathe it is fairly easy to cut down the counterweights. Calculate how much bobweight needs to come off and then convert that to cubic inches of steel and you'll know how much depth to take off. We cut the counterweights down at the shop when we have to take off a lot of weight since drilling big holes in the crank is a bad idea. Once you know how to do it the task goes pretty quickly. If you do the calculation correctly you can often hit the balance number very closely so the final balancing only requires a dimple or two.
View attachment 1715234894
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I would be interested in how a guy figures that out !!
 
Here's my guess as to how it might be calculated:
A particular counterweight's thickness and radius is easily measurable. So is the weight's fraction of a complete circle around its circumference (number of degrees out of 360 degrees). Treat the counterweight as a solid cylinder with volume t * pi * r^2*. Density of 4340 steel is about 0.284 lb per cubic inch. Multiply it all and I'll bet it's close enough for minor drill adjustments since the amount removed is a small fraction of the counterweight diameter.
(An accurate calculation would be more complicated since you have an original radius and a new cutdown radius). More likely it is just common knowledge that you knock off .120 and go from there :rolleyes:
 
I’m just wondering if I were to take .120 off and then knife edged it if I would end up being too light.i wouldn’t want to have to add Mallory to it. Kim
 
I always wondered about knife-edging... supposed to make the leading edge slip through the oil mist easier or something. Does it actually show measurable benefits on a dyno?

Notice that all low-drag airplane leading edges are not knives, but round and blunt in the front, with a long tapered trailing surface. Has anyone machined a crank that way instead?

Anyhow, for my 451 (KB 280 pistons which are fairly light, and Eagle rods) they took .120 off my steel 440 crank and it did need some heavy metal to balance. Don't remember what the parts or bobweights were though.
 
It's complicated because some mass is rotating, and some is reciprocating, so they have different values. The large and small ends of the rod must be weighed separately, using a fixture and you need a bearing and ring pack mass. Locks are mostly about 4gms.

Bobweight Calculator - Performance Engine Tech

Engine Balancing, Part 5 | Eaton Balancing

I try to contour the CW's and throws with shedding oil in mind. I'm not sure how effective it is, but it seems to be more prevalent in the circle track and road race stuff where you have accel and decel cycles. Drag race is basically just a single cycle load test. S/F....Ken M
 
If you're just weighing the parts, anything with .5gm accuracy that can scale to 1000gm is fine. By the time you buy something decent, you could have paid for the balance job. I've going to send you a PM. S/F....Ken M
 
I would trim the counterweights slightly less than calculated ( maybe Andy would do the math for u, I would 20 years ago), then i suggest a trial assembly to check for clearances etc.
 
oldkimmer said:
I’m trimming the counterweights down to lighten the crank, not for clearance. Kim
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oldkimmer said:
I’m just wondering if I were to take .120 off and then knife edged it if I would end up being too light.i wouldn’t want to have to add Mallory to it. Kim
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I refer you back to post #2 where it says, "very little drilling"
 
IQ52 said:
I'd think about cutting the counter weights down. When I built the 451 stroker with a factory 440 steel crank, I cut the counter weights .120" in radius for use with 6.76" H-beam rods and Ross forged flat top pistons. Took very little drilling on the crank after that to balance it.

My pistons were 510 gms and the pins were 158 gms. Scat H-beam rods for 2.375 journal.

Ask those that are going to do the balancing for you.
Click to expand...

I'd be curious instead of taking .125 off of all of them in a flat fashion on the lathe how far you could knife edge each counter weight and achieve the same weight savings
 
You can take off a lot of mass by rounding and smoothing the CW's and cleaning up flash and sharp edges from the original forging. BUT, it won't be nearly as effective at removing bobweight as lathe turning, because you're working at a closer radius to the crank centerline. It's just like torque, force times distance. An equal force/mass at twice the distance from center is twice as effective.

What I did with my factory crank projects is to go apeshit with the grinder first, then send it off to get the journals ground(if needed), nitrided and then do final balance, lathe turning etc etc. S/F....Ken M
 
oldkimmer said:
Has anyone tried to lighten the stock crank before balancing? My new pistons and rods are 251 grams lighter per cylinder. Would I be better off to get a lighter aftermarket crank? Thanks. Kim
Click to expand...

Just did a 505 balance job the other day. Had to take 0.050 off the counterweight OD to remove 60 grams from the bobweight. What did you end up doing with this engine? Was the 251 grams the difference in bobweight, or just the difference in weight?
 
I got the counter weights turned down .120 thou. The place that’s gonna balance it actually figured I could take .150 off and be pretty close. He does excellent work. We will see in the new year. The 251 is the difference in just the weight. Kim
 
DrCharles said:
I always wondered about knife-edging... supposed to make the leading edge slip through the oil mist easier or something. Does it actually show measurable benefits on a dyno?

Notice that all low-drag airplane leading edges are not knives, but round and blunt in the front, with a long tapered trailing surface. Has anyone machined a crank that way instead?

race stuff!
Click to expand...
 
this is a very , very interesting exercise . There should be a sticky on this . I t will save a lot of grief for future builders like myself . Good luck with your project , guys .
 
My project has ground to a halt for the most part. I got a seasonal camping spot and that put a big hole in my engine budget. I’m still collecting parts. Kim
 
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