Engine balancing

Question...Is a stock 350 internally balanced? If so what does one have to look for?

See if you have weights on the flexplate/flywheel or if holes were drilled to remove mass.
Internal balanced assemblies have only holes drilled into the crank counterweights, you can swap flywheel/flexplate and balancer as you like.

Yes, a 350 is internally balanced

An external balance flexplate and damper will have a big counterweight, it's very easy to spot.

It depends the later 350s had a rear external balance and none at the front.

guru said:

It depends the later 350s had a rear external balance and none at the front.

Click to expand...

Correct-- but just the one piece seal engines did that. All the 2 piece seal engines (350 small block) did the internal balance. They make a plate to balance a flywheel for use on a one piece seal crank.

i'm aware that this is an old post.

Anyway. If pistons, or conrods, are to be replaced, the engine should be rebalanced?
I guess that new components most likely are of a different weight that originals.

I'm asking since I'm rebuilding a 350 which already have forged pistons. I found most of the conrods out of spec and need to replace them. I see that new are of different weight!

If this is the case it might be cheaper for me to buy a complete rotating assembly?

naasaa said:

i'm aware that this is an old post.

Anyway. If pistons, or conrods, are to be replaced, the engine should be rebalanced?
I guess that new components most likely are of a different weight that originals.

I'm asking since I'm rebuilding a 350 which already have forged pistons. I found most of the conrods out of spec and need to replace them. I see that new are of different weight!

If this is the case it might be cheaper for me to buy a complete rotating assembly?

Click to expand...

Just have it balanced

Just checked the cost for rebalancing!
Here in Denmark, $700 :huh:

About the same as a rotating kit exc. shipping and tax.

Ouch!

IF your pistons are good as far as wear, along with all the other parts, you can always get a neew rotating assembly with all forged parts then sell the old stuff. Might offset some of the cost..

700 BUX?? Lord love a Duck......Last engine I had done here was 150 bux....

been a while, BUT it was in Wash DC too, high cost area...

a trick I found out about balancing, most GOOD/GREAT engine shops are out in the boonies, or work very odd hours,....it was explained to me that is because the balancing gear is so sensitive that even with rubber mounts, and isolation techniques, it will pick up truck traffic, let alone trains....

so is done out in never never land or at 3am when not even the devils are out....

somehow if looking for a fine enough job, good to 50,000 rpm or whatever, it seems right, so I believe it....


:clobbered::nuts:

naasaa said:

Just checked the cost for rebalancing!
Here in Denmark, $700 :huh:

About the same as a rotating kit exc. shipping and tax.

Click to expand...

Crap!!:crap::crap::crap:

Anyone who knows the weight of the original piston from a 71 350?

Must add that I'm an engineer working with recipricating medium speed engines.
I know that the weight (Balancing) of the counter weight is important. However, they are fine tuned for a specific engine speed.
So, how much would I be of if I installed new lighter weight conrods and pistons than the crankshaft were balanced for original, but the weight of all 8 new units are equal?

Any ideas?

Pardon my peanut brain, but I thought it needs to be balanced for the connecting rod & pistons not being of equal weight.
If carefully selected and they are within a couple of grams I thought balancing wasn't necessary. I could be wrong though.
Comps sells a little device that allows you to balance your rods yourself.

http://www.hdmaddog.com/Comp-Cams/Part-search/Comp-Cams-POW351245-Match-p6686560.html

http://www.compperformancegroupstor...re_Code=PH&Screen=PROD&Product_Code=POW351245

Home made setup here:
http://www.angelfire.com/ca4/CorvAIRCRAFT/RodBalance.html

Imo

I didn't express myself clearly (talking bout peanut brain!)

The weight match of rods and piston is clear. I made a device similar to your home made link, though simplified.
My quoestion as that the crankshafts counterweights are balanced for a certain conrod and piston configuration. Now that I replace these with lighter rods and pistons, should I then re-balance my crankshaft?

If necesary I will do it, but if not I'm waisting a lot of money.

My quoestion as that the crankshafts counterweights are balanced for a certain conrod and piston configuration. Now that I replace these with lighter rods and pistons

Click to expand...

My farmer's intuition says no.
The crank would be balanced for unequal weights at different locations, not the weight itself.
So with all equal weight heavy con rods & pistons replaced by equal weight light versions should not require re-balance.

Caveat: if you replace uneven weight heavies with equal weight lights you would need to re-balance.

I stand ready to be corrected and edumecated though....:clobbered: