I promised to post the results of the balancing of my brand new ZZ4 GM short block. This came assembled, so I had to pull the pistons and press out the pins. I have to assume that since this was assembled by GM, that these weights were within their tolerance for a balanced engine. All of these weights are in grams.

Pistons Rods Pins Pistons & Pins
1 533.9 598.5 159.8 693.7
2 531.4 600.8 160.0 691.4
3 533.8 601.5 159.4 693.2
4 533.6 600.8 159.2 692.8
5 530.8 599.2 159.7 690.5
6 533.3 596.1 160.0 693.3
7 533.5 602.4 159.4 692.9
8 534.8 596.9 159.6 694.4

As you can see, the greatest difference between two pistons is 4.0 grams and 6.3 grams for the rods. There is not too much you can do with the pins to balance them. And the piston and pin combination is the end product that counts. Just think of large rocks at the end of sticks twirling around, you sure would want them to all weigh the same. After balancing the piston/pin combination, they all weigh 690.5 +/- .1 grams. We threw the pistons on the scale and they all weight 690.5 or 690.6 grams. The rods were balanced to 596.1 grams +/- .1 grams.

The balancing was done by Ed's Crankshafts in Hayward California. The shop is run by two brothers, Ed and Carlos. I have know both for years and Ed's wife used to work for me years ago. There are not too many crank grinding shops left in the area. Ed's does most of the cranks for the East and South Bay machine shops.

The GM balance may be okay for those that drive down the freeway or side roads at no more than 2500-3000 rpm. But if you want an engine that will run smoothly and last....BALANCE IT.

 

Good info John, Thanks.

 

How do they balance it ? If one weighs more and another weighs less ?

May sound stupid, but how ? Shave a small piece ?

 

Material is removed from boths ends of the rods and both sides of pistons(pin boss).

 

Haven't checked the rods on how they did it, but on the pistons they use a drill and remove small amounts. Never actually drill a hole, but the taper of the bit. They remove a small amount and then weight it, remove a little more and weight it again.

 

Thank you for posting weights of the reciprocating components.

Do you have information from their work with the rotating assembly?

.

 

So there must be a spot, where material can be shaved and not cause weakness.

Thanks for the info

 

So balancing is just matching the weight of the components?
I thought that you had move the weight forward or backward of the rods.

And what about the flywheel and harmonic balancer?

 

Was always curious of the differences in weights of factory parts.
Thanks for posting-interesting.

 

Great info, thanks.

 

When you internally balance an engine,you use a neutral flywheel or flexplate and harmonic balancer.
Rods have small"pads" where material can be removed.He said how they do it to pistons.
After they have the rods,pistons balanced,they balance the crank using the weights they came up with during the process.
Make sure the guy gives you the card that says what the balancing weights were so if you have a problem in the future,like say a piston go,you dont have to pay to rebalance everything.
Some shops will not give you the balancing card so if you have a problem,you have to go back to them because they know the weights.

 

I don't have the crank balanced yet! I took off the flex plate which I was told out bolt up to the ZZ4 crank and took that. the crank and balancer in to Ed's. They called yesterday afternoon to say it was the wrong flex plate!!! Nothing it town, so one should be in at 9:00 AM this morning from Sacramento.

I should have listened and double checked....research on the Forum said NEW FLEX PLATE. Trans shop said the old one was okay.

 

CF C4Tech : 1
Trans Shop: 0

For the benefit of others who come across this thread, perhaps
consider discussing why the OEM flex plate from the '85 is incompatible
with the later ZZ4 design.

.

 

The flexplate you have and the ones one those motors stock were for externally balanced motors.They use the balancer and/or flexplate to balance the motor.
As soon as you internally balanced the motor,you need a neutral balanced flexplate and balancer.
Some guys will want the neutral balanced flexplate/balancer when they balance the rotating assembly to double check it is really neutral but they dont need it.As long as you are buying a well known quality flexplate and balancer,it should be neutral.
Be careful as some cut corner shops will want the flexplate and balancer because they are really balancing the motor using the flexplate which is what the factory did and is not what you want for a perf build.
Make sure they are INTERNALLY neutral balancing the motor if thats what your paying for.

 

My main point was if he is truelly internally balancing your motor,he should not need the flexplate to balance the crank.It should be done by adding/taking away weight out of the crank where needed and not taking or adding weight to the flexplate to compensate.
Then just buy a neutral flexplate and balancer to bolt on and get the card with the rotating *** weights incase of future problems.

 

87L98Z52 It's just not done that way. When you carry in your spinning assembly, you better take the flexplate/flywheel and harmonic balancer with you or they will send you back home to get it.

It is safe to "lighten" a piston as there is always extra meat on there that can be safely shaved off. There are hundreds of little secrets to engine building. Some people share them, some don't.

Balancing is the last thing you do after setting piston ring end gap, getting rods the same length (offset hone the big end to get all of the center-to-center lengths the same) Even aftermarket rods must be checked. The block has to be checked from the crank centerline to the top of the deck, front to back. Bellhousing flange has to be checked so the transmission mates true.

If I am inside an engine, I at least balance the pistons. I weigh rings, wrist-pin, cir clips as a unit. Rods are balanced end-to-end and then total weight.

A hot trick is to shave the cranshaft weights .125 in a lathe. This makes the spinning mass smaller. Weight is brought back up using mallible iron, drilled crossways through the crank weight and welded in place. The left side (drivers side) of the oil pan rail can be shaved so oil slinging off the cranshaft can return to the oil pan as quickly as possible. A crank scraper can also help along with a windage tray.

Years ago I built an engine for Popular Hot-Rods Engine Masters series. My budget was $5000. Rules were: cast iron heads, pump gas, no gear drives, flat top pistons and 355ci. My engine made 520hp and survived an hour on the dyno. I'm not sure how many pulls they did but they were working out a software glitch....My engine was the one that made the most pulls. I learned a lot from the other builders and they learned a few things from me. I would use a crankcase vacuum pump next time....

 

I am sorry but i disagree.When you Internally balance an assembly,you dont NEED the flexplate/balancer.
When you buy a balanced assembly from eagle or others,they do not have your flexplate or balancer do they?
Its why they tell you to buy a neutral flexplate and balancer.
That is why they call it internal balance.If you are using the flexplate to balance the assembly,its not internally balanced.
If i have a internally balanced motor,i should be able to switch a neutral flexplate with another neutral flexplate with no problems.
If you are altering the flexplate to balance the engine,it not Internally balanced.

 

If the dampener and flexplate are netural and the crank is balanced. The largest question is BALANCED BY WHO'S STANDARD?

See Balance Part II

 

Many different versions of "close enough" or "within spec" vs. spot on.

 

Here is a picture of the piston that required no alterations and one that had material removed. If you look closely, you can see that material was also removed from the rod. When the rod is weighed, they want all of them to weigh the same. BUT they also weigh each end of the rod and remove material so that all the small ends weigh the same and all the large ends weigh the same. You can also see the heat image on the end of the rods where they were heated to easily insert the pins.



Here is a picture of the ZZ4 block before installing the pistons.



Progress is being made.