Ive a crankshaft thats going to need approx 330 grams removed to balance it out.

When I toss it in the lathe to remove some from the counterweights is there any way to determine how much to remove or at least not go too far?

TIA!

I believe the counterweights are drilled to add or drilled to remove.

Yes, just measure the width of the counterweights and their length to give you the area. Then the depth of the cut will give you the volume. Multiply by the density of steel and that gives you the weight you are removing. Same process as drilling the crank to balance it but instead of using the size of the hole to calculate the weight you use the volume of material turned off the counterweights.

Trouble with turning the counter weights is if the amount you need to remove isn't in the center of the counter weight itself. Leave yourself some extra weight to fudge it.
Doug

My crank was enitially balanced by Crower by machining counter weights down. But like Doug stated, you will have to cut a little, check the balance, and repeat as needed till you gain more experiance in balancing that way.

Thank you for the informative replies.

Pretty grey area for me. What im wondering about is drilling 330 grams out of a scat cast crank extreme?

I use to have the approx figures of how much weight was removed by drilling but can no longer find them.

Thanks.

How did you come up with a figure of 330 grams. You can cut the counter weights down a little but you need to leave enough weight there to be able to drill where it is needed.

The machine shop I use in Eugene, OR , Southward LLC, doesn't drill the counterweights when balancing, they do grind down the counter weights to get them balance
They done around 100 + motors for me in the last 15 yrs with no issue on balancing or their machine work other than them wanting to make holes on the small size instead of on the large size like I wanted them for the first 3 motors
All is good now

Thats what my intentions were was to take a bit off for less drilling.

The weights simple, lightweight scat I beams and small bore short skirt stroker pistons. Crank should be 2050 from the box and I was using approx weight from a similar build and with the parts I will use im getting 1698 grams. So in reality im looking at shedding 350 grams.

The math is easy if you use 100 grams per cubic inch for steel. If it was me I'd cut 3 cubic inches off the counterweights and then spin it on the balancer. 3 cubic inches is probably less than 0.100 of depth but you need to measure the length and width of your counterweights to be sure. Do you have a rigid setup on your lathe that will let you cut the counterweights without chatter? We tried some different setups over time and eventually hit on a carbide cutter and a feed and speed combination that produces a mirror finish with very little noise. But the setup has to be dialed in and rigid.

Andy I have the lathe but not the machine. My lathe is old old but still good enough I used to cut my own cam blanks and send them to crane for lobes.

I guess what im getting at is this.... can they drill 350 grams out of the crank? Yea I could call and ask but if I dont get the one guy who does my work im not gonna get good info.

I do have a option im not thrilled about it though as id like to use the scat rods, ive a nice worked set of old dc 340 rods that are a bit lighter then stock 340 rods I just put arp-s but would need to get them resized which would put me at 1972 grams on the 2050 crank so that would be an easy balance.

131.72 grams per CI

I cut the weight off on the lathe for every Stock Eliminator or Superstock crank that I do but the time required is significantly more. I am able in most cases to get it perfect without drilling holes by using a angle grinder with a flapper disc to remove weight where required when you are very close. As far as removing that much weight from a cast crank it is no different than removing it from a forged crank


Max Weg

Yes I know. But the math is easier if you use 100 grams. The final 30 grams per cubic inch is taken off either by drilling or hand shaving. You want to leave it a little heavy when it comes off the lathe since balance point usually has to be moved a little off center.

So if you were a back yard hack with plenty of time, Would it be better to drill a set of radial holes further in -1 1/2"? to effectively undercut the bobweight?
You would have to remove more weight that way to make the balance work? On the theoretical side it would be better to keep the diameter as large as possible and remove weight from the centre yes?

I spose my real question is, is there any reason not do that? I have a 440 crank to jam into a 383 block and I was considering doing just this. Ive seen where you turn the bobs down to 7.25 to get close on weight and clear the pistons, my target bob is around 2165 so a bit more would be warranted.

And yes a new one would be better, but I have the 440 crank already that mags fine and after shipping and taxes its under 1/2 the price of importing one to oz even after the cost of the offset grinding to 3.9 - if i bought a new one i would have to sell the 6.7 k1 rods I already have too as a new one would be 4.25 stoke and I would then need 6.535 rods, Im pretty certain im better off chasing hp in the heads vs the cubes $$ wise at this stage

Sorry for the thread jack, but it seemed pertinent to the OP

A 440 crank needs to be turned down anyway to clear in a B block so you fix two problems at the same time when you turn the crank.

Hi folks,

Read this a few times now about 440 cranks in a 400 block!
I heard it’s approximately 0.125 of an inch.
Is that the depth or overall off the diameter?

Wonder how much weight that actually is?
I was gonna use aluminium rods anyways, so that’s cool...