swapping pistons and balancing

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63dartman

63dartman

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I have a thread started about 302 castings and it went into rotating assembly balancing.
here is the dilemma, I just picked up my rebuilt 360 bored 60 over, stock dish type pistons, I also purchased speed pro pistons CP116 to change them out and increase the compression a tad. Do I need to rebalance the rotating assembly or not? I can't find any info on piston weights to know for sure. I was told if the speed pro are within 3-4 grams of the stock ones balancing could be skipped.
Also need to know what everyone is using to press the pins out without damaging anything.

And lastly, If balancing is not needed is it safe to change the pistons without removing the crank?

Man I feel like a rookie!
 
nevermind on the balancing question, I read some previous articles on balancing and all the names I recognize as mopar pro's say that balancing is the only way to go..... I think I am just going to give them back the engine and have them replace the pistons and balance at the same time.
 
Sanguine said:
factory balance job is not a good one...their tolerances are very wide...
Click to expand...
This is true. My 360 from the factory was way out of balance on the machine even though you'd never know it cause it didn't shake before I took it apart. Man I'm glad I had it balanced!
 
Heck, I've had local shops' "balanced" jobs in front of me. My shop's machine is computerized, and can get within .1 grams. Their old school spin balance machine got it as good as they could. And it was still 18grams out. The factory balance can be as bad as 30 grams.

Just saw the other post. Have it balanced.
 
FWIW, When I had my 360 rotating assembly balanced with Eagle SIR rods and KB107 pistons (both of which are significantly lighter than stock parts) they had to remove all most a pound of material from the crank to balance it.

The CP116 pistons are much lighter than stock so I would go for the balance for sure.
 
Also, the lighter pistons could be run on the stock crank with the balancer and flexplate. It's not a great situation, but the better of the possible out-of-balance situations one can have. Out of balance means just that, and brings with it all the down sides of that situation. But heavy in the crank is much less of a big deal than heavy on the reciprocating side of the equasion. You could also just spin balance the crank to the lighter bobweight, if you find the average piston weight of the new set. Then it's 1/2 a balance job.
 
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