1978 Z28 4-speed...Just completed a ZZ430 buildup with individual parts , mostly new direct from GMPP and some bought new on eBay. (ZZ4 block w/steel crank, used powder-metal rods, new Mahle pistons, Fast burn 385 heads, LT4 hot cam setupw/roller rockers, vortec RPM manifold.Engine starts up fine, runs ok but begins to develop a vibration at 2500rpm's and gets significantly worst at 4000rpm's, does it standing still or cruisin'. Everything is brand new including the flywheel, clutch and pressure plate. Nothing was checked for balancing cause I "ASSUMED" brand new GM parts were already balanced.
I got some people stumped on this one. Any help or ideas short of tearing it down again will help!

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Are you saying you didn't balance the rotating assembly at all?

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Fred
94 Formula A3: 381/TH400/N2O

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11.513@115.59 on motor; 11.162@127.67, 1.643 60' on a 125-shot. Going with a 275-shot this year

 

Make sure you have the correct harmonic balancer. Generally, for the setup you have it should be a 8"....

 

Unfortunately, once again out of stupidity, I assumed that all the new parts were zero balance from factory. Hard lesson to learn unfortunately especially after doing this for 25 years!

I do have an 8" balancer that was from an original ZZ4 engine.

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"ZZ4 block w/steel crank, used powder-metal rods, new Mahle pistons" doesn't quite sound like "new parts zero balance from the factory".... .

Try balancing the parts you can access easilly... clutch and flywheel (is engine internal or external balance?).

Fred

 

Fred, if you check the spec sheet for ZZ4's, they come with powdered-metal rods with Mahle hypereutectic pistons with low tension rings (9.6:1 comp ratio).
As for balancing, the first way I will go at this by removing the 4-speed and seeing what happens and then removing the clutch/pressure plate /flywheel and have the 2 checked for balance. Thanks for the input.

 

Also if you notice when you buy the crate Motor complete it comes with a flywheel with a weight attached to one side, the newer one peice rear motors are not fully internally balanced.
Perry

 

Perry, I think you're absolutely right and this is the crux of the issue here, that factory new parts are NOT balanced the way they should be. We decided not to buy the actual crate motor but build our own according
to buildup specs on a ZZ430 using all brand new GMPP. Even when you pay real good $$$, you'd think the parts were all perfectly balanced. Go figure!

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You can buy a
$3000 LA Enterprises Crank
$3000 Set of Crower Titanium Rods
$900 set of Diamond Pistons
$300 ATI Damper
$300 CSI Flexplate

and its STILL gonna need Balanced.

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Kurtis Tamez
LT4-396.com
97 Z28 LT4-396
94 Firehawk LT1-396
Team NW F-Body