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-   -   BALANCED rotating assembly (http://www.hotrodders.com/forum/balanced-rotating-assembly-226103.html)

377MONTE 11-14-2012 11:50 PM

BALANCED rotating assembly
 
I am looking into a few of the different balanced rotating assemblies available for a 377/383 stroker build. need some help here.. :confused:

Eagle sells a BALANCED external balance 383 rotating assembly that comes with a new flexplate and harmonic dampener. Will this pre-balanced kit be good enough to drop into the block and bolt up, or will i need to have my local machine shop check their work and rebalance it???

gearheadslife 11-15-2012 12:46 AM

double checking is always a good thing.. but..
if you has an engine balanced at one local shop would you then bring it to another to check the first shops work?
can't hurt having it rechecked.. other than your wallet..

cdminter59 11-15-2012 12:55 AM

BALANCED rotating assembly
 
Does this kit have a cast or forged crank? Are you using I beam or H Beam rods. To be on the safe side I would have it checked out.

BOBCRMAN@aol.com 11-15-2012 05:46 AM

Most of the kits that I see are not very close on their balance job. Usually + - 5 gr. or sometimes + - 10 percent. A machine shop will usually use a + - 1/2 gr. balance.

engineczar 11-15-2012 06:10 AM

I've also seen cases where the components used to set the bob weight differ from what was sent in the kit. As an example in one case the weight of the rod bearings on the balance card was way off from what I measured. According to the description the kit was supposed to come with Clevite bearings and it actually shipped with Kings which were about 8 grams heavier.

hcompton 11-15-2012 08:07 AM

an externally balanced kit can also be balanced or unbalanced from the factory. So yes externally balanced and purchase prebalanced with the rods pistons crank flexplate and balancer. These kit will usally turn 6K but if the engine is going to live at 6K its not as good as internally balanced.

The pre balanced kits on an external blanaced engine are as good as the oem do when they slap them together. that being said the factory was not building a 6K rpm engine. I have seen them work just fine being slapped together. I have also seen them go to the machine shop and need lots of work to get right. factory balanced usally just means they weight the kit parts and make sure they are all with in the spec for a balanced kit. not sure about eagles process they say alot of fluff on the site but it doesnt seem to be the case when the kit lands on your door step. That being said dont buy the none balanced kit because guess where all the parts that were out of spec went... One piston too light and your F'ed. Every piston will have to be modified to make up for the difference then the crank shaved to make up for the lighter pistons. yada yada yada...

Internally balanced is good but the cost is alot more initial and more time at the machine shop. But if your going for full race motor you will need it for 6500 or 7K rpm engine.

gearheadslife 11-15-2012 08:10 AM

Quote:

Originally Posted by BOBCRMAN@aol.com (Post 1611434)
Most of the kits that I see are not very close on their balance job. Usually + - 5 gr. or sometimes + - 10 percent. A machine shop will usually use a + - 1/2 gr. balance.


my 496 kit was very close.. but I bought mine through scott shafiroff racing, and that might be why.. they prob. balanced it.. not eagle..

vinniekq2 11-15-2012 08:56 AM

names like shaffiroff/lukovich/mitchell all have big names,(there are others) usually supply good parts.My friend John Graham races in Calgary and uses Shaffiroff parts,My parts came from Jeff Lukovich,no complaints so far

ap72 11-15-2012 11:13 AM

Quote:

Originally Posted by BOBCRMAN@aol.com (Post 1611434)
Most of the kits that I see are not very close on their balance job. Usually + - 5 gr. or sometimes + - 10 percent. A machine shop will usually use a + - 1/2 gr. balance.

Depending on what it is 5 grams is well within the acceptable range for anything on the street. In fact most engines on the street won't be within that spec from the factory. 10% on the other hand can mean a LOT when you're dealing with a 1700 gram bob weight- that would be 170 grams.

377MONTE 11-16-2012 01:03 PM

i just got off the phone with Eagle, and their techincian Tim assured me that the BALANCED 383 kits like they sell on summit or jegs are already balanced +/- 2 grams. He said they undergo the same balance job as their race balanced rotating assemblies and i would be able to open the box and install. (after making clearances on the rods and block of course) :thumbup:

techinspector1 11-16-2012 01:10 PM

Quote:

Originally Posted by engineczar (Post 1611440)
I've also seen cases where the components used to set the bob weight differ from what was sent in the kit. As an example in one case the weight of the rod bearings on the balance card was way off from what I measured. According to the description the kit was supposed to come with Clevite bearings and it actually shipped with Kings which were about 8 grams heavier.

Thanks for weighing in with this info.
As I have said many times on this board.....TRUST NOBODY.

ap72 11-16-2012 01:14 PM

FWIW, I have swapped pistons to something MUCH heavier and ran the engine without balancing. And many others run race engines that way too. I'm not saying balancing isn't a good thing to do, but I've ran engines just fine without it.

The other issue is that when balancing there is actually only a very small window in which any balance job is perfectly dynamically balanced. Something I wonder about when you see race engines going to anywhere 48-55% balance when 50% is believed by many to be the absolute perfect number for a V8.

junior stocker 11-16-2012 01:57 PM

I think they are about as accurate as a "factory balanced" engine is. It's pretty close, but can be greatly improved on. Here's my story: Many years ago I bought a "balanced kit" to build a 334 CID engine using a 305 block and a cut down 400 crank. Turned out the 305 block I had, the main bearings had spun badly, and it was junk. So, I just hung onto the kit until a good 305 block was given to me years latter. After it was together, and in the truck, something was'nt right. It would idle fine, but start to drive, it was like it was pulling a battleship, and had a "dull" feeling to it. I actually parked the truck for several years rather than mess with it anymore. Then one day, in a magazine, I saw a layout of several Chevrolet flywheels and flexplates. WHAT??? That can't be right. Took off the converter shield and.............FOUR-FIFTY-FOUR flexplate!!! Swapped to a 400 flexplate, and it's been smooth sailing since. California Discount Warehouse must only balance their engines to "known, general specs", without balancing them WITH the dampener and flexplate on the rotating assembly, and put a 454 flexplate in the box. My truck had sat for six years, and I had the kit stored for probaly another six before that, so forget about any kind of warranty or compensation. Now I take MY PARTS to MY MACHINIST, because the others obviously can't be trusted. Butch/junior stocker.

CNC BLOCKS NE 11-16-2012 03:12 PM

Quote:

Originally Posted by ap72 (Post 1611975)
FWIW, I have swapped pistons to something MUCH heavier and ran the engine without balancing. And many others run race engines that way too. I'm not saying balancing isn't a good thing to do, but I've ran engines just fine without it.

The other issue is that when balancing there is actually only a very small window in which any balance job is perfectly dynamically balanced. Something I wonder about when you see race engines going to anywhere 48-55% balance when 50% is believed by many to be the absolute perfect number for a V8.

Engines like cup enignes that spin over 8000 RPM alot of those cranks are over balanced. The blower engines I build I over balance be 2% as they spin 9500 and no problems.

Machined a block for a customer and the pistons were appox. 72 grams lighter and they said it would be fine. Now that they have runn the engine they are going to take back apart and balance the rotator like I said needed to be done.

CNC BLOCKS NE 11-16-2012 03:16 PM

Quote:

Originally Posted by 377MONTE (Post 1611969)
i just got off the phone with Eagle, and their techincian Tim assured me that the BALANCED 383 kits like they sell on summit or jegs are already balanced +/- 2 grams. He said they undergo the same balance job as their race balanced rotating assemblies and i would be able to open the box and install. (after making clearances on the rods and block of course) :thumbup:

I have seen one of there prebalanced kits and one end of the crank was off 36 grams.

Whats really interesting when you buy a prebalanced kit the pistons are in a sealed box the ring are in a sealed box and rods are still in the plastic sealed wraping HMMMMMMMMM


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