Engine Balance Counter Weights - Engine-Balancing Basics

Ishigo says that while the electronic balancer can read each counterweight individually, he generally treats the engine as front-half and back-half setups. Because this Ford is an externally balanced engine and so much weight had to be removed, Ishigo's first step was to remove 77 grams from the bolt-on offset weight in the Professional Products balancer. But keeping the amount of weight removed from the front and rear symmetrical required removing metal from the crank counterweights on both ends. So Ishigo set the crank in a large lathe and removed more than 400 grams from the front and rear of the crankshaft. The amount of weight removed was limited by the height of the rod journals on the opposite side of the counterweights. When the lathe just barely touched the rod throws, the cutting stopped. Next, he removed additional weight by drilling multiple holes in all the counterweights. Ishigo decided to drill three shallow holes in each counterweight rather than two deep holes, removing another 82 grams from the rear, roughly similar to the 78 grams removed from the balancer. Ishigo says that drilling multiple holes is safer because it's shallower, but drilling holes alongside the direct path of imbalance is also less effective than removing weight directly in line. It comes down to how much weight must be removed. We added up the total weight removed from the crank, and it came to just under 1 pound, 4 ounces. While not a huge amount compared to the overall weight of the entire rotating assembly, it still equates to a lighter package that will rev a little quicker and help acceleration.

Most balance shops are not equipped with a large lathe like this one at Scat, but this is a great alternative to drilling an excessive number of holes in your crankshaft.
Most balance shops are not equipped with a large lathe like this one at Scat, but this is
The farther the holes are drilled from the opposite side of the rod journal, the less effective the weight removal becomes, but often drilling multiple holes is the only way to balance the engine.
The farther the holes are drilled from the opposite side of the rod journal, the less effe
Here is a screen shot of the electronic readout of a Hines balancer after Ishigo finished drilling the small-block crank. Note that the amount of total imbalance in the entire assembly is less than 1 gram.
Here is a screen shot of the electronic readout of a Hines balancer after Ishigo finished

SBC Strokers
Another area of potential confusion lies with the extremely popular 383ci small-block Chevy stroker packages. The 383 originated using a 400ci engine crankshaft in a 350 block. As mentioned earlier, the 400 was the only small-block that was externally balanced, and most 383 kits retain this external balance feature. But for higher-end applications using a 4340 forged steel crankshaft, the ideal path is to internally balance the rotating assembly to reduce crankshaft flex. Now let's make this more complex by using a one-piece rear main seal block and crank. With a Lunati Sledgehammer crank and rotating assembly, this is exactly the combination used in the 383 small-block that was our test engine for the giant parts-test story "Are Premium Parts Worth the Price?" in the Sept. '07 issue.

It's easy to spot the weight for the flexplate on a one-piece rear main seal flexplate (arrow). This will need to be removed for an internally balanced 383 stroker. Note the multiple holes drilled were necessary to zero-balance this one-piece rear main seal flywheel, which had been originally built for an externally balanced application.
It's easy to spot the weight for the flexplate on a one-piece rear main seal flexplate (ar
Here is what Mallory metal looks like in a crankshaft. Note that the weight is added horizontally, which is much more secure than adding the weight vertically into the crank counterweight.
Here is what Mallory metal looks like in a crankshaft. Note that the weight is added horiz
This is what happens when too much weight on the end of the crankshaft is combined with lots of rpm.
This is what happens when too much weight on the end of the crankshaft is combined with lo

At first this would seem simple, since you don't have to use an offset weight balancer or flexplate/flywheel. However, a one-piece rear main seal rear flange does not allow for the offset weight that is used on a two-piece rear main seal engine. To account for that weight difference, all one-piece rear main seal flexplates (and flywheels) require an offset external weight. But with an internally balanced crank, this weight is not necessary. Thus in the case of a flexplate, the external weight must be carefully removed. For flywheels it's possible to have a zero-balance flywheel custom made. If you already have a flywheel, additional holes can be drilled to bring it back to a zero-balance condition. If this is not done, the engine will experience a vibration that will eventually tear up the main bearings and cause damage that could easily be avoided.