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Engine Rebuilder Trader International magazine

Crankshaft Balancing Tips # 1
Gary Thompson, ABS Products

After 50 years in the balancing industry, I have found that over half of the balance shops don't know that the bob weights should be located in the center of the throw. I get at least two or three calls a week from shops that are freshening up a motor and find that they need to rebalance the crankshaft. They find a 4 to 12 gram differential from end to end. The question I ask the caller is, "Have you ever taken your bob weights off and put them back on the crankshaft?"

No matter how good you are, when using universal bob weights you will most likely be off a couple of grams. It's hard to get it perfect.

When the bob weights are pushed to the "rear" of the crankshaft, the result is that the rear of the crankshaft is overbalanced and the front is underbalanced. Conversely, pushing the bob weights to the "front" of the crankshaft causes the front to be overbalanced and the rear to be underbalanced. Either way it is a very minor amount of weight and the crankshaft is still well within industry standards.

When the bob weights are placed in the center of the throws the couple balance will be the same throughout the crankshaft.

Balancing Flywheel and Clutch Assemblies
Gary Thompson, ABS Products

When using a cone-type flywheel mandrel, the first thing to do is check for run out. Some flywheels may have a machined chamfer and are not concentric with the register. If they are not concentric, the surface will not be running true.

I personally prefer to balance flywheel and clutch assemblies using a crankshaft or a mandrel like a crankshaft. The clutch needs to be preloaded as if a clutch disk were in place, with three lightweight spacers 120 degrees apart that are the same thickness. This keeps the pressure plate parallel with the flywheel. I've seen as much as one ounce of unbalance when the clutch plate is not preloaded.

Many clutches fit in the register of the flywheel. Others locate off of special clutch bolts with shoulders. Still others locate off of dowel pins. Many diaphragm clutches locate on every other hole. Make sure you use the clutch bolts that fit the registered holes. When using a cover that was designed to fit on flywheels register, but it's being bolted on through loose holes need to be indicated concentrically and dowel or roll-pined to locate. All clutches and flywheels should be marked so that they always repeat in the same location.


Gas station owner in high school, shop, got into balancing in 1955. Built fixtures to make the jobs easier and faster, which is how ABS Products came into being. ABS Products and Automotive Balancing Service became separate companies in 1987.

In the old days your motor had to be blueprinted and balanced.

Blueprinting could have been a valve job or a complete rebuild top to bottom, front to back. But, it always had to be balanced. "Balanced" was a buzz word in the 60's.

Today, if you are a full line machine shop, it's the final step in selling the component parts and the rebuilding/machining process. Regardless whether you are a machine shop or a shop that specializes in balancing, it is the last major operation before assembly.

You can be either the hero or the goat, depending upon how happy the customer is when you have finished.

  1. Does the engine run smoother than they remember it before it was balanced?
  2. Does it go faster than before it was balanced?

Always remember, happy customers don't talk, whereas unhappy customers tell, it seems, everyone.

Balancing can be as simple as match-weighting the parts, making up and installing the bob weights and drilling a hole; or it can be as difficult as trying to drill the hole in an incredibly hard crankshaft and installing several pieces of heavy metal, drilling the backside of the throws or cam turning the counterweights.

Discuss balancing different motors - simple to hard.

Different traps to watch for:

  • Buick flywheel flanges that are symmetrical
  • Crankshafts that are:
    Out of phase, forging twisted, incorrectly bent
    Ground improperly
  • E-bay basket case assemblies that aren't matched to each other:
    Internal parts for external motors
    External parts for internal motors
    Adjusting for one or two exceptionally light or heavy parts.

Emphasize that you have to make money. Time is money!

Any good owner knows how much they have to charge to keep the doors open - this number has to be included in any job that goes out the door.

When pricing a job you have to consider:

  • The cost of opening the doors (electricity, insurance, rent, taxes and other related payments)
  • The cost of employees (salaries, sick days, uniforms, insurance [workers comp, health], taxes and other benefits
  • The cost of maintenance and upkeep of the equipment (not just the balancer)
  • The consumables you will use (drills, reams, cutting oil)

Balancing a crankshaft that takes 8 hours to do between drilling, reaming and installing heavy metal. Things to consider:

  • Figure time
  • Figure materials (consumables)
  • Figure materials to balance it (parts)
  • Figure the freight to get the parts to you

Running a engine rebuilding or engine building shop in these tough times is a challenge for everyone. If we can be of some help please call us today at 714-671-0728.

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