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Tour of an Engine Rebuild Shop

Part 5: Pistons, Rods, Crankshafts and Balancing

By Jeremy Wilson

With the block cleaned and machined, Portland Engine Rebuilders fits the new pistons and then goes to work on the crank and connecting rods.

“Once the pistons come in we measure each one and then hone the block to fit the pistons for the final fitment,” said Ted. “Everything is hand-fitted once we’re finished, to get a perfect fit every time. The crankshaft goes over to the crankshaft department to be checked for straightness, and then it gets magnafluxed.

“Then the crank is reground and bearings are ordered after we know what size the crank was ground to.

“The connecting rods are reconditioned and resized, and finally, we swage in new wrist pin bushings and hone those to size.”

People often use the term “balanced and blueprinted” about their engines. Ted describes what those terms mean.

“Blueprinting is a slang term used in the industry. In 30 years of working on engines, I’ve never seen an exact definition. To me, blueprinting is when an engine is designed, the engineers create a blueprint with precise coordinates as a specification. We have a blueprinting center with a Rottler CNC Machining Center that works based on coordinates, and by that definition, we can reproduce those specifications in our shop. But “blueprinting” by itself is a slang term.

“Balancing, however, is a term that a lot of people use in the same sentence. About 50% of the engines we do get a balance job. We do static balancing and dynamic balancing. Pistons are brought to identical weight to plus-or-minus ˝ a gram. That’s our shop specification for “in balance.” Connecting rods are hung horizontally and the big ends are weighed separately from the little ends. Those are match-balanced to within a ˝ gram tolerance.

“Then the crankshaft, flywheel, harmonic balancers and clutches get a rotational dynamic balance job done on our Balance Technology balancer.

Another phrase that gets thrown around is “internally balanced.” Ted explains that too.

“There are two different styles of balance jobs - and it depends on the engine manufacturer. Most Chevy small blocks, for example, are “internally balanced” or “neutral balanced” - those are the same thing. They have no counterweights on the harmonic balancer or the flywheel. So we balance the crankshaft, then add harmonic balancer, the flywheel and pressure plate and balance those. So at the end of the process, it’s an assembly.

“But once the small block achieved 400 cubic inches, they became externally balanced with counterweights on the harmonic balancer and the flywheel. On other engines, such as Fords, Chryslers, and all big blocks, they all have to be counterweighted. They’re all balanced as an assembly.”

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