Can I fit standard 312 pistons to a 292 without a problem? Should I do a sonic check before boring?. I guess(?) that is about 60 over on the 292. Are the wrist pin locations the same? And the big question, Is it worth it? Chuck in NH

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Chuck:

The 312 pistons are .050 larger than the 292.  It would be a rare block that couldn't stand that.  Is it worth it?  If you already have the pistons, it's well worth it.  If you have to buy pistons, go to about .030 over 312 to 3.830.  That's what I do in the Hurricane, and supercharge it to sometimes 14 psi in the manifold.  No cylinder wall problems.

John

John - "The Hoosier Hurricane"

John,

Thanks, that about what I thought. I do have a new set of 312 pistons with rings so boring would be the only big expense. I guess I'll go with that. 

Next question. Can you use an ounce scale for balancing pistons or is gram that much better? Thanks again. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Chuck:

The gram scale seems to be industry standard, so it must be better.  Ted will probably delete this message since he is in the balancing business, but what I use is a balance, compare pistons until I find the lightest one, then use that as a standard to lighten the other 7 to.  Do the same to the rods, small ends and total weights determined the same way.  Then I take a sample piston, pin and lock rings, rings, rod, and bearings to my machinist and have him balance the crank.  Saves me a few coins and saves him some time.  Oh yeah, the pin diameters and compression heights are the same for 292 and 312 pistons.

John

John - "The Hoosier Hurricane"

John.  I'm hurt to think that you think I'd delete your message.  But you're absolutely right in the balancing process for the pistons.  Find the lightest piston and then modify the remaining seven so they all all the same weight.  Just be careful in where the weight is removed so that the strength of the piston is not adversely affected.

A gram scale is used because of the greater resolution.  There's approximately 28.7 grams per ounce so the amount of precision becomes greater with a gram scale versus that of an scale that measures in ounces.

Lorena, Texas (South of Waco)

Ted,

          Does John mean that you think he's unbalanced? He's accused me of that! And it's possible.

                                                           Frank

Frank/Rebop

Bristol, In ( by Elkhart) 

Gee, is it unbalanced, inbalanced our out of balance?

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Gee, I'm sorry Ted that I hurt you.  Now I can recommend that Moonshadow send his parts to you to be balanced.  Then he'll be mad because I recommended shipping them halfway across the country when he could have it done by a local shop.  I can't win.  Maybe Frank has it right, I'm unbalanced.  Oh well.

John

John - "The Hoosier Hurricane"

Moonshadow:

Ssshhhh.  Don't let Ted hear this one.  I have a feeling you are leaning toward making the 312 pistons weigh the same as the 292 pistons and assembling the engine, accepting the "factory balance" as OK.  If this is your plan, I would determine the "average" 292 piston and match the 312 pistons to that one.  I kinda expect Ted to chime in here and tell us how far off factory balance really is.  Hope I didn't hurt him again.

John

John - "The Hoosier Hurricane"

Hello John.  Yep, I heard you.

The factory balance is like all the other variances within the engine as it falls within a given tolerance when performed at the factory.  Some rotating assemblies would appear to be in the ball park while others are at either end of the spectrum or range.  This is just one of the things within an engine that would explain why identical engines perform completely differently.  Those engines that are at the ends of the balancing specifications or ranges are the ones that ultimately have early wear issues and in worst case scenarios, actually have vibration issues that can be felt in normal driving.  Having an engine or rotating assembly balanced by your local machine shop falls in that blueprinting category where you're striving to get everything just 'right' and much closer than factory tolerance.

If an individual were to merely match balance the stock pistons as well as the small and big end rod weights, then that in itself would be a significant improvement regardless of the where the crankshaft balance originally was.  When making a change in the piston or connecting rod weights, then the crankshaft does need to be rebalanced accordingly.  The crankshaft is the piece of the puzzle that has to be done by some specialized equipment so it's difficult for the average garage guy to do this piece but the rods and pistons are fair game if not going overboard with the lightening process.

I trust this helps to understand more about why to balance.

Lorena, Texas (South of Waco)