How much weight change before you rebalance crank. New rods .020 shorter but heaveir on small end. Big end almost same .By almost I mean less than 10g. Small end on other hand is 240g old rods 275g on new rods. My thought is I can probably get most of it off pistons or at least half of it. One reason I will be putting another set in later anyway. Probably heavier than ones in motor since .125" bigger Would rather do that than grind on new set of $1500 MGP rods. Guessing difference is billet rod just denser material and heavier. If matters its billet crank also. Motr will probably rarely see 8000 rpm and if so will be brief flash . Correction below on weights of rod ends up dated10-24

This message has been edited. Last edited by: wideopen231,

Not sure who I would trust to rebalance this crank since KB is no longer making cranks original manufacture is out of question. Few local guys do balance work most I would not trust to balance a bicycle wheel. Piston,pin.rings and rod weight 1955 grams if that helps new combo with old pistons is 35 grams more.

This message has been edited. Last edited by: wideopen231,

Chris,

Figure up the percentage of over or under balance of your old setup. Then figure where the new rods put you.
Then you can decide if it is where you want it.

You probably know this but, most times you would go 50% if it is normally aspirated. I go 52 percent with my blown application. Minimum 51%

I just had mine re-balanced because new pistons were 60 gr heavier than other set. A sad story..

Dave

Chris, depending on the bobweight your crank is balanced to now (I'm guessing 2200-2400) you will be way too far underbalanced. It doesn't take much to pound the mains out of your type of engine and underbalanced just makes it worse.

Good luck with your project(s)

quote:

Originally posted by wideopen231:
How much weight change before you rebalance crank. New rods .020 shorter but heaveir on small end. Big end almost same .By almost I mean less than 10g. Small end on other hand is 240g old rods 275g on new rods. My thought is I can probably get most of it off pistons or at least half of it. One reason I will be putting another set in later anyway. Probably heavier than ones in motor since .125" bigger Would rather do that than grind on new set of $1500 MGP rods. Guessing difference is billet rod just denser material and heavier. If matters its billet crank also. Motr will probably rarely see 8000 rpm and if so will be brief flash .

You will NOT get that much weight out of the piston.

Of its off by more than the 35 grams difference it had always been off. Crank was balanced by KB to weight of old combo. Never knocked mains or rod bearing out of it.Rods now that is different story. Have broken few rod bolts and half wrist pins once(different story).If anything combo in it now is lighter than original since it had Ross pistons which are very heavy compared to Venolia's that are in it.

Will pull front main and see what is stamped on throw.

This message has been edited. Last edited by: wideopen231,

NUMBERS ON CRANK FROM kb ARE 6497 AND 2515.

One thing that might help is new piston designs are good amount lighter than they where 20 years ago.This is well aged parts.

Now on using numbers I gave on rod ends.Not exactly measuered using correct setup,more of a A&T engineering set up for quick reference.LOL Total rod weight is about only part I would testify if under penality of perjury.

This message has been edited. Last edited by: wideopen231,

quote:

Originally posted by imakehp:
Chris, depending on the bobweight your crank is balanced to now (I'm guessing 2200-2400) you will be way too far underbalanced. It doesn't take much to pound the mains out of your type of engine and underbalanced just makes it worse.

Good luck with your project(s)

Please explain how it is the mains are pounded out easily. Not arguementive although suresome will see it that way.

To my understanding Hemi's have always been the strongest design bottom end and reason most late model engines are of similar design as far as Y block design giving crank support.

This message has been edited. Last edited by: wideopen231,

I have a balancing setup for rods and scales.Going to get some actual numbers this week.Got to dig them out right after I remeber where I have them. Have to have then for a set of 327 rods for ol school project that I want to polish and balance rods and pistons for.

Little more info although not perfect setup its hell of lot better. rotating weight is 1217 and recipicating 1355. old was rotating 1088 and recip. 1346. so 2434 vs 2572. crank stamped 251. 5o 2.5% over crank or 6% over old combo.old was 3% under crank numbers. Then small percent is lot when dealling with 2500.

Looks like rebalance before running new rods. Probably not issue since ones in car have 10 runs in TA/D and maybe 12 to 15 hits in NA trim. Its those first 10 that concern me. We changed them at 15 to 20 runs in funny car and dragster for a reason. Then they where Only 600 per set at the time.

Imakeho,

Although off subject I would like yout thoughts on why this style engine will knock mains out easily? Always like hearing different reasoning even if don't agree totally.