what you are considering is not worth the gamble. That .2 oz. could very well weigh a couple of pounds at 5000 RPM. Too much at stake to risk. :anim_25:

 

I wouldn't put them in with the .2 oz difference, i would have them weigh they same
, and i doubt very much i will be running this at 5K it's going into a street car a real street car, not a race car on the street.

 

It should be fine. Some engine builders put extra bob weight on the crank anyway. It's called overbalancing, and it's quite common. Since your new combination is lighter, it's the same thing.

To do it absolutely correctly, you really need the small end and big end weights of the connecting rod. To balance, you use 100% of the connecting rod big end weight (plus the bearing), and 50% of the small end, plus 50% of the piston, pin, and rings. The extra weight I referred to above means you would use 52% of the piston/pin/ring/small end weight (+/- depending on builder preference).

You would not want to go the other direction unless you were overbalanced with the initial balance job.

One warning - this applies to an engine that's been balanced by a good shop. If your engine has only the factory balance, I'd get it balanced by a good shop - or at least weigh the risk. Factory balance is OK but not excellent, and there are exceptions that are not so good. Balancing by a good shop is much more precise.

 

I haven't weighed all of the dimple/ forged piston assemblies yet, i weight two of them and both came to the 3lb 15.8 oz, i plan on getting all them cleaned up, and then weigh them all, and get them all to weigh the same, if i need to remove any weight from the rod/ piston assembly, where could i take it off? Or should i just leave as is?

I know most of you guy's have the bucks to do to do everything by the book, but alot of us can't afford that luxury, we must improvise, we want to have fun th well i'll shut up now.
Thanks Jim

 

I don't know what your new rods look like, but most factory rods have a "balance pad" where you can safely remove weight with a grinder or belt sander.

On factory pistons, there's usually someplace on them where you can drill at least a couple of 1/4" diameter holes x 1/4" - 3/8" deep. Maybe several. A 1/4" hole x 1/4" deep flat bottom hole is 8 grams.

 

I don't know what your new rods look like, but most factory rods have a "balance pad" where you can safely remove weight with a grinder or belt sander.




On factory pistons, there's usually someplace on them where you can drill at least a couple of 1/4" diameter holes x 1/4" - 3/8" deep. Maybe several. A 1/4" hole x 1/4" deep flat bottom hole is 8 grams.

There GM factory bbc Dimple rods, and yes i know the pads on the end of the rods are used for balancing assy, and areas on the pistons also.

 

Not knowing what bob weight your stock cask crank is balanced too, It would be worth it to get it balanced and take all the guess work out!!

 

As I posted earlier, it's not worth the gamble. If you should put it together without balancing and if you are like most people, every time you think you feel a vibration in the engine or think you hear a strange noise you will immediately think it's a balancing problem. Just remember people who give advice don't have to live with errors.

 

balance

Have it done by a pro. You'll be glad you did. Back in the day a guy I hung out with had a 58 Vette 327 ported and polished balanced with a Isky 505T roller cam that when the carbs were balanced correctly he could stand a dime on edge on the air cleaner. He was awfuly proud of that.

 

Have it done by a pro. You'll be glad you did. Back in the day a guy I hung out with had a 58 Vette 327 ported and polished balanced with a Isky 505T roller cam that when the carbs were balanced correctly he could stand a dime on edge on the air cleaner. He was awfuly proud of that.

I applaud him for that, that's great, but that is not what i'm trying to attain with this engine.

 

Ok, another question, Gm made several different stock versions of the 454 Gen lV - V and they used different pistons' some flattops some dished and some had different rods, but they all use the same stock crank , flexplate and dampner, i'm not talking about the GM performance bbc.I haven't weighed these different stock pistons and rods, but i would be leaning towards that they don't weigh the same.:confused0006:

 

I ask again. Can someone try to answer this?

 

4lb 1.0 oz. - 3lb 15.8 oz = 1.2 oz = 34 grams.

Guys who balance performance engines generally shoot for 1 gram or less. The factory may have been happy with 20-50 grams. How close are the rods to each other (big and small ends), and was all your current stuff balanced as an assembly? If it was a factory job, you could be way out of balance with the new pistons. At the least, I'd try to lighten them a little in the pin boss area. 1.2 oz may be a tall order, though. I'm not sure if removing weight from the small ends of the rods has the same effect on balancing as removing weight from the pistons. Stands to reason it would.

Cool looking car, by the way. I really like the wheels and stance. What are the rear wheel and tire sizes? Did you tub it, or just move the springs?

 

14lb 1.0 oz. - 3lb 15.8 oz = 1.2 oz = 34 grams.

Guys who balance performance engines generally shoot for 1 gram or less. The factory may have been happy with 20-50 grams. How close are the rods to each other (big and small ends), and was all your current stuff balanced as an assembly? If it was a factory job, you could be way out of balance with the new pistons. At the least, I'd try to lighten them a little in the pin boss area. 1.2 oz may be a tall order, though. I'm not sure if removing weight from the small ends of the rods has the same effect on balancing as removing weight from the pistons. Stands to reason it would.

Cool looking car, by the way. I really like the wheels and stance. What are the rear wheel and tire sizes? Did you tub it, or just move the springs?

Thanks Mike for the compliment.
Rear wheel 10 x 15 tires are MT sportsman pro 28 x 12.50 x 15.Springs moved inbd and a mini tube.

14lb 1.0 oz. - 3lb 15.8 oz = 1.2 oz = 34 grams. thanks mike for correcting me.

 

Gm mass ballances cranks based on a bob weight for a given batch of engines. so to answer your question they are reasonably balanced based on application. they are not all the same. and if you get a replacement crank it has to be balanced also

 

Thanks hotdog, gotit.

Is there

some way to find out what bobweight was use to balance a stock crank?

 

Not knowing what bob weight the crank was balanced to its a good idea to have the crank balanced to what you are using for rods, pistons, rings, locks if floated and rod bearings.

I have seen on the 604 crate engines that I have had to rebalance a few of them do to the cranks being 40 to 44 grams under balanced.

 

If you had the original pistons and rods you could weigh those. It would get you close but is a big crap shoot as the factory ballance is so rough (20-40 grams). I recently had a 427 that was "balanced" by a shop of unknown. it shook so bad it rattled the dash screws loose in my camaro. I spent the cash to have it balanced and it was smooth as any thing else I have had . A good balance job can have numerous benefits. smoother running, cooler running, better ring seal, better bearing life,more hp and best of all more MPG. I know you are trying to keep this engine on a budget but it is just sooo much better when balanced. especially if you are already dissasembled. best of luck

 

Just to help clarify things a little. When an engine is "balanced", there are TWO balance weights that they are working with. Reciprocating weight, and rotating weight. Reciprocating weight is made up of the small end of the rod, the piston pin, and retainers if used, the piston, the piston rings, and a "nominal" amount of oil that would natually coat the parts while in use; it is the weight involved of the up and down motion of the piston assembly in the cylinder. Rotating weight is the big end of the rod, the rod bearings, the dampener, the flywheel/flexplate, and some machinists also include the clutch assembly, and again, a "nominal" amount of oil; this makes up the spinning/rotating assembly. Therefore, all the engines parts need to be separate in order for balancing to be done. Pistons, already on rods, can't be balanced, nor can the small end of the rods be balanced with the piston hung on it. First all the reciprocating parts are weight matched. Then the rotating weight is computed, and a bob weight is arrived at. Once the bob weight is arrived at, the crankshaft can then be balanced by removing or adding weight to the crankshaft balance weights as necessary to arrive at the bob weight/balance weight figures. This is done on a machine that spins the crank and bob weights, and has an attached drill used to to lighten the cranks balance weights as needed. Adding weight is rare, and more involved, and very doubtful for a street engine. Of course a stobe light is used to pin point where weight needs to be removed/added. Overbalancing has already been discussed, and is primarily for race type engines. Factory balance is an "in-the-ball park" sort of deal. Even replacement pistons, including those in oversizes, are again, an "in-the-ball park" weight of factory pistons, so as not to have to redo the factory balance, but factory balance is far inferior to a machinst balancing all the engines parts/components. It is amazingly cheap what balancing costs relative to the time it takes, and the equipment used. That's a basic, simplified explanation.......I'm not a machinist, I'm not a DR., and I don't play one on T.V.; I'm a retired X-Ray Tech., and I appreciate what my machinist does for me. Butch/56sedandelivery.

 

GOOD POST

I had a customer call a few weeks ago I did all the machine for the engine they assembled it and said balancing was a waste of money now its vibrating and they are concerned now, I replied balancing a waste of money as you told me. Now they have to do the job twice, I wonder how much they really saved???

I have one of those old Stewart/Warner green balancers with the strobe light great machine but it does not tell you how much as to come out or exactly where it has to be drilled and it not a very fast machine.

I did up date to a Hines balancer which is very fast and accurate.

 

I stayed at

a Holiday Inn express last night.
and I still don't know.

my 2 cents..... spend the $$$ and balance it,
the way my luck runs, it would shake itself apart if I tried it with out!
I'm in Kingman, and my local guy gets $200 to $250 to balance a V8.

 

I balance even the stock rebuilts (altough, its very hard for me to leave anything stock... ) it makes a much happier engine!