Balancing a crankshaft thoughts?

[old31]

My engine builder suggested balancing my crankshaft for $700 while everything was apart.

1: What are your thoughts on doing this?

2: Is $700 a fair price?

The car is driven on the highway at 50-55 MPH with a 5.5 head, larger intakes, B cam grind, and FSI zipper.

[Kevin in NJ]

Will not hurt if done right.

Before he touches your crank ask who grinds the cranks and to what specs. He should know the factory print specs and work to them. Does he check the work on a surface plate.
I know this sounds like a lot but this is critical to get done right. Some consider .002" acceptable for the flywheel off center, some dont. We have a crank ground with the flywheel center at .008".
Contrary to what some might tell you, crank grinders can mess up your crank in ways you might not expect. Unless you have access to a surface plate you may never know there are problems. From centerlines on the mains not being on center to each throw not having the same throw. Add in the critical getting the flywheel on center line and you have a lot of things a grinder needs to keep to thou accuracy. If the shop does not think that is needed then you best go elsewhere if you want a car that will run 50,000 miles on a rebuild (the babbitt should last that long).

Then ask what he does for the rods. If he does not weight match each end as well as total weight then counter balancing the crank is a waste of time cause you will have a potential larger problem with the rods taking everything out of balance. Ford spec was +-1 gram at each end. A set of rods and pistons were within 4 grams in the engine when the car came off the line.

In the end, it is not about all these additions, but about getting the job done right.
The extra $700 spent on counter balancing is a waste if the system is not in tight balance and well done.

[Dodge]

For $700 that must include adding counter weights on the crank then balincing the whole motor.
If it's just balancing the crank it should $200 or less.
$700 is fair if he is doing everything including the counter weights.

[jhowes]

Can someone explain what a "surface plate" is. Jack

[Bob Bidonde]

To be effective, balancing should include all rotating parts including the crankshaft, flywheel, clutch disk and pressure plate. Counterweights added to the crankshaft counteract the crosshead loads of the connecting rods.

All should be spin balanced, not static balanced.

All of the above for $700 is reasonable.

[Kevin in NJ]

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A surface plate is a piece of granite that is very very flat like much less then a .0005" variation over the surface. You can then use precision measuring tools to accurately measure something. It is how you need to check the dimensions of a crankshaft between the parts.

[jhowes]

Thanks Kevin, I knew someone would know. Jack

[old31]

Thanks guys.