highhilleer

If it was originally a 289, then it is definitely 1968 or older. However, the balance is based on the crank, not the block. The block is static; the crank spins. I do not know if a 50 oz balance crank can be used in a block that originally had a crank with a 28 oz balance. There could be slight design changes to the block that would keep the cranks from being interchangeable.

slickman

I think which one (28oz or 50oz) you use depends on which harmonic balancer you use, not the crank.

highhilleer

You are right that the harmonic balancer and the flex plate or fly wheel must be the same balance. But selection of 28 or 50 oz is dependent on the crank, or more correctly, the whole rotating assembly, including rods and pistons. If you simply change the harmonic balancer and fly wheel from 28 oz balance units to 50 oz units, you will get a lot of vibration and damage.

slickman

Yup, you're right. One would hope that who re-built it would stick with the period correct rotating assy.

Clu7ch

isn't the harmonic balancer the piece that is either 28oz or 50oz? from what i can gather the harmonic balancer is off-weighted (28oz or 50oz) to balance out the crankshaft. since the crankshaft is not a straight piece, it will wobble without something attached to it to keep counter weighted, hence the harmonic balancer.

in short, yes, you are correct. which one you use (28 or 50) will depend on the harmonic balancer you use. either a 28oz counter balance or a 50oz counter balance depending on your crank.

lets say you have a 302 and stock, it has a 28oz imbalance. you take that 302 and stroke the motor to a 347, now you need a 50oz imbalance, nothing with the motor changed other than the bore. all you did was run different pistons, connecting rods and a crank with a slightly different stroke, requiring a larger counter balance.

all in all, your harmonic balancer's imbalance will all depend on the type of crank you are running.

rmodel65

the balance changed around 82!

Clu7ch

thats fine, first off i didn't give a year and secondly, all i was doing was making a point. if you wanna get on me for the specifics, prove me wrong while your at it. and if you can't prove me wrong than


i'm not here to start crap with others. i'm here to help and learn and have a few laughs. now, all i said was, depending on the crank you use and the throw it has you may need to use a different balancer.

rmodel65

not to be rude i was just didnt want someone to get the wrong one

Clu7ch

na, it's cool. it just seemed like you had aimed that at me for my last post. cars are a royal PITA to do anything to even something as simple as a 5.0. thats why i prefer OLD cars, carb'd motors. you need an electrical degree more than mechanical knowledge to work on cars anymore and it's a damn shame. there has got to be a way for this person to find their matching H/Ber. how that is, i don't know.

rmodel65

any casting on the block after e2=82 is a 50oz and so on f=90s
c5=65 c6=66 etc would use a 28oz
also all 351w use a 28oz