balancing

[Cougar948]

I have just decided to rebuild my 351W again. AM going with a mild to medium sutup. .030 over w/ hypereutectic pistons, stock stroke, AFR 185 heads, airgap intake, RPM cam, am interested in spinning every last one of those 6500 RPMs on occasion. Am also adding new eagle rods to strengthen on my stock items now. Heres the kiker, engine is currently balanced. When installing my new rods would yall recommend pulling the crank(what Id like to not do) or just have the rod/piston combo balanced. What would happen if I just said screw the balancing? And If yall have any input on what line of rod feel free. Hopefully yall can add some encouraging suggestions.
Thanks,
Ryan

[auto10x]

If you want to have a smooth runner with durability, you'll want to have it balanced. You get what you pay for.
auto10x
Bill

[trularin]

Any time you change a weighted item, the assembly should be balanced. Even if it is a check.

It is worth the HP and smoothness to have it done.

Just my $0.02

[vettestr]

Cougar958
If engine was balanced in current state and there is NO ISSUES you need to resolve then dig out your old balance ticket. It has a list of all the individual weights that made a balanced assembly. The combination of a rod, piston, rings, and bearings added together are the BOB WEIGHTS that is then hung on the crank and spun up to find the counter balance needed on the crank/crank, flywheel and front damper. one is for internal and the other is external bal. The factor of big end or small end of the rod also determine reciprocating weight.
If you need to replace 1 or 2 pistons etc.. on a balanced assembly all you need to do is replace with the same total or BOB weight and the engine is still a balanced assembly.
If you replace all or 1 of the piston assemblies and the weight is more than 2 grams different (many have different allowable standards) the engine is NO LONGER A BALANCED ASSEM.
Engines will go through 2 extreme or maximum harmonic vibration RPM ranges. An engine that has been balanced has had those 2 extrems moved to a RPM that is for the first below the useable and the 2nd above the useable RPM range of that engine. Unbalanced engines have a much smaller deviation or window where they go through those 2 extreme ranges and both will be in its usable RPM range. This imposes additional stress on the reciprocating assembly and the amount is relative to amount of imbalance.
In short, buying better quality products and then ADDING extra stress by not having them brought back to even the factory (much less strict) standard is not how you built everything else I'll bet.

[vettestr]

Cougar958
If engine was balanced in current state and there is NO ISSUES you need to resolve then dig out your old balance ticket. It has a list of all the individual weights that made a balanced assembly. The combination of a rod, piston, rings, and bearings added together are the BOB WEIGHTS that is then hung on the crank and spun up to find the counter balance needed on the crank/crank, flywheel and front damper. one is for internal and the other is external bal. The factor of big end or small end of the rod also determine reciprocating weight.
If you need to replace 1 or 2 pistons etc.. on a balanced assembly all you need to do is replace with the same total or BOB weight and the engine is still a balanced assembly.
If you replace all or 1 of the piston assemblies and the weight is more than 2 grams different (many have different allowable standards) the engine is NO LONGER A BALANCED ASSEM.
Engines will go through 2 extreme or maximum harmonic vibration RPM ranges. An engine that has been balanced has had those 2 extrems moved to a RPM that is for the first below the useable and the 2nd above the useable RPM range of that engine. Unbalanced engines have a much smaller deviation or window where they go through those 2 extreme ranges and both will be in its usable RPM range. This imposes additional stress on the reciprocating assembly and the amount is relative to amount of imbalance.
In short, buying better quality products and then ADDING extra stress by not having them brought back to even the factory (much less strict) standard is not how you built everything else I'll bet.

[Mr.Fixit]

Yes, must balance. One of the most necessary $100 bills you will spend.

[George Snyder]

Cougar,

I agree it should be done by all means. If you plan on spinning that engine to 6,500, I would also suggest you have it blue printed.
Bud

Mr. Fix it,

$100.00 is really cheap!
It cost at least $200 here on the East Coast!

[Mr.Fixit]

Last time I paid for it, it cost me $100. That was a few years ago. That was also at a shop that only does balancing, nothing else.

[George Snyder]

Mr. Fix it,

You Guys on the West Coast are fortunate to have shops like that still available! Our "Speed Shops" sell more Truck Accesseries than speed equipment. Things sure have changed over the last 35 years!
I had my SBC done about 7 years ago and it cost me $189.
(moment of weakness). It cost the engine builder quite a bit though. It seems he thought he would take a little short cut, and save a couple of bucks on the build.(lump sum). Well it seemed to him that since they were all new pistons, why balance rotating assembly?
Engine back in the Car and found out that there was a distint vibration at 2,500 rpms. Engine back out, torn back down, and reassembled, and reinstalled. All for $189! The kicker si that it was in my 76 Vette. All the room in the world right?
Take care,
Bud

[Cobra #42]

Cougar, My .02 worth, use a better piston than a hypereutectic, spend a couple more dollars and get some good forged pistons. And always check the balance, cheap insurance. db

[Cougar948]

thanks guys ill prolly look into what you have said....the more information the better thanks again
Cougar948