Engine Balancing & Assembly

If you are running aftermarket components (a different crank, different rods, and/or different pistons), then ABSOLUTELY you want to balance that engine! None of those aftermarket components are balanced to work with each other, nor do they weigh anything close to the factory components they are replacing, so it is an absolute MUST to balance any custom built engine using aftermarket internals.
Engine Balancing & Assembly
There are 2 ways to balance an engine. The first is weight matching. This is done by weighing all of your pistons on a balancing scale. Once you find the lightest one, you then remove a little metal from the others (in a place that won't weaken the part) until they all weigh the same. Parts are usually measured within a quarter gram.

This procedure is then done to the connecting rods. Once they are all done, then the rod is weighed on a balancing fulcrum which determines how heavy the rod is at either end. If one rod is a little heavier on the big end (where the bearing goes) than another, a little weight is removed from the heavier one to balance them out. After that is all said and done, the next step is dynamic balancing. This is when the rotating assembly (crank, rods, pistons) are put on a machine (sort of like a tire spin balancer) and the counterweights of the crank are weighed against the piston/rod combo. If a light weight set of rods and pistons are used, then usually a little material needs to be taken out of the crankshaft to even it out.
Engine Balancing & Assembly
If a heavier set of rods and pistons are used, then weight usually needs to be added to the crank weights. This is done by drilling holes into the crank counterweights and pressing in cylinder shaped slugs of heavy metal known as Mallory metal to increase the weight. Street engines do not necessarily need balancing. Except for a couple of rare occasions, almost no factory engine ever came fully balanced, even most "performance" engines weren't balanced.

Balancing helps an engine run smoother with less vibration which creates less havoc on main bearings and helps things last longer.

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