Engine balance

[matt5112]

Our motors are externally balanced.

The N/A and S/C balancers and flex plates are both different from one another due to the mass of the rods and pistons.

View topic - Illustrated Rebuilding of a L67 from a L36 : PontiacBonnevilleClub.com

L36 Rod: 633g (rod, cap, and bolts only..no bearings)
L67 Rod: 688g (rod, cap, and bolts only..no bearings)
L36 Piston w/wristpin: 497g
L67 Piston w/wristpin: 554g

For example:

My motor is a stock L36 with the L36 flex plate with an L67 balancer.

That'd suggest the front end is overbalanced compared to the back end of the crank.

Consider a rebuild with different pistons as per previous link:

And last, here's the replacement pistons I am going to use: Federal-Mogul Sealed Power PN H871CPA 0.030 overbore.

Replacement L67 Piston w/wristpin: 560g

Seems about normal considering its a 30 over piston.

Haven't found a mass number for the L32 rods yet.

However if I were to rebuild my motor with L32 rods and the sealed power pistons, I'd have to have the bottom end balanced.

Even as is, the bottom end is technically not 100% balanced due to the wrong balancer being installed.

Quite the curveball thrown into the whole top swap idea.

Anyone else have thoughts on this matter?

Flexplate and balancer for an internally balanced motor exist as well.

Between Meziere and Powerbond that is.

To venture in a different direction, at one point I was under the impression the S/C balancer and N/A balancer had the same balance.

More on the balancers: http://www.precisionparts.com.au/Raw...ogue2009sm.pdf

As per this, there is a small counterweight and a large counterweight.

This catalog claims both N/A and S/C models use the same counterweight.

http://www.precisionparts.com.au/Raw..._US_Single.pdf

This catalog claims the L36 and L67 can use the same balancer no problem.

You get stock counterweight or no counterweight (internal balance)

This leads me to believe balancers are all the same balance, yet the flex plates are different?

Back onto flex plates:

http://www.gmforum.com/showthread.php?t=293006

Bill says.... its all okay.

So the L26 and L32 share a flex plate?

[BillBoost37]

Bill actually offered it as a suggestion. Scimmina and Agrazela are the two sources I found out from about the balance being different.

I have mixed and matched flexes to a degree w/o problems or issues. I have not fully done the research (great info btw) on the longevity or true balance issues associated with top swapping.

And..I'd be asking the long term, successful top swap guys which setups they used. There might be a reason why some swaps stay together and some rip bearings apart. Most of us will blindly say, it's the tune. What if it's more than only the tune?

[Bio248]

i had mismatched flex plate and balancer for a long time and never had any issues.

my bearing issue was me not putting the oil pump gear on for the first 3-5 one minute startups.

[matt5112]

I'm not sure it really matters all.

The more I read, the more it seems the general really had poor quality control.

3800Pro.com Forum - View Single Post - 3800 OILING -TECH- analyzing deficiencies

However the SIII covers have larger oiling ports compared to the SII covers.

Heres the post: 3800Pro.com Forum - View Single Post - 3800 OILING -TECH- analyzing deficiencies

That mentioned the L67 rod/pistons varied in weight by as much as 5 grams.

Yet the powered metal rods from the L32 are much closer to one another.

Which is quite significant considering the motors weren't internally balanced at all.

Heres another source with rod masses: Rebuilding the 3.8L Buick Engine: Engine Builder