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#919543 - 02/21/12 06:59 PM 383 and balancing?????  
Joined: Mar 2001
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Crisco Offline
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Crisco  Offline
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Posts: 248
Jacksonville, Florida
Built a 383 years ago. When I researched everything I found I needed a externally balanced dampner and flexplate. That's whats on there, but now that I think back to when I was building it I had the machine shop balance the rotating assembly. It really wasn't expensive either. Well I researched some and sounds like its pretty expensive to have it all balanced cause the metal they use.

So my transmission went out on me so I'm ripping that out and my question is whether or not I need to put a neutrally balanced flexplate on. Its just been so long since I built this engine that I can't remember exactly what I done at the machine shop



1986 SS, 383/200-4r/3.73 Gears

#919548 - 02/21/12 08:14 PM Re: 383 and balancing????? [Re: Crisco]  
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MADMIKE Offline
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MADMIKE  Offline
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C.V. CA
The 383 stroker uses a 400 or 400 based SBC crank. The 400 used external couterweights on the harmonic damper and flexplate unlike the other SBCs which were internally balanced.

The rotating assembly is balanced as one unit. That includes the harmonic damper, crank, rods/pistons/rings/bearings, and flexplate. If you need to change the flexplate due to damage you need to make sure to use the same type, most likely a 400, and have the new flexplate balanced to match.

I would not install a neutral/internal balanced flexplate on an external balanced engine, vice-versa, or any off the shelf flexplate/flywheel onto the engine without first confirming with a machine shop what kind of balance/imbalance the flexplate has.

Installation of an incorrectly imbalanced component on the engine would induce unwanted bending loads, unwanted vibrations, and eventual damage to the engine along with possible damage to the transmission.


-Michael
Where the hell is JMD?!
#919602 - 02/22/12 12:33 AM Re: 383 and balancing????? [Re: MADMIKE]  
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BuzzLOL Offline
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Toledo, Ohio
.. X 2... sounds like your 383 was simply balanced like a factory 400... with unbalanced 400 flexplate/flywheel and unbalanced 400 front damper... and pistons/rods/crank simply/cheaply balanced to match those components... like the factory did it...

.. The expensive balancing you're reading about is using Mallory Metal to do a totally internal balance of an engine's rotating assembly... so that balanced dampers/flexplates/flywheels can be used...a good idea for a high RPM racing engine, since it reduces stresses on the crank, but not usually needed for a budget mild street performance build...

.. The '86 and up SBC V8's with 1 piece rear main seal are kind of a hybrid of the two balance types with a balanced front damper, but an unbalanced flywheel/flexplate... this is because the new crank re-design allowing a seal to slip over the now perfectly round rear of the crank eliminated an unbalance weight that had previously been cast onto and part of the rear of the crank(as opposed to being part of the flywheel unbalance).


'86 Monte LS (total'd Fall '2013), '87 GTA TransAm TPI350 TH700-R4, '85 Fiero 5-speed, '75 MG Midget Buick Alum.V8 BW 5-speed manual, '77 Pontiac Astre Formula wagon 5-speed posi, '78 F150 4WD 351"M ==> 400" C6, '79 Caddy Seville Olds EFI 350" TH400, 19' Slickcraft 425HP 351W MerCruiser I/O
#919631 - 02/22/12 03:15 AM Re: 383 and balancing????? [Re: BuzzLOL]  
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86ttop Online grandpa
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86ttop  Online Grandpa
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Brooksville, Fl
IF it has a large chunk of steel on it, it is a 400 flexplate and you'll have to make sure you replace it with same.


Leo Paugh
It's not an attitude, it's just the way I am.
POW*MIA
You are not forgotten
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#919646 - 02/22/12 11:35 AM Re: 383 and balancing????? [Re: 86ttop]  
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Crisco Offline
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Crisco  Offline
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Jacksonville, Florida
Ya I have a 400 flexplate and the right dampner on now. So I guess that is what the shop did then. Well that makes me feel better....thanks guys!



1986 SS, 383/200-4r/3.73 Gears

#919648 - 02/22/12 12:10 PM Re: 383 and balancing????? [Re: Crisco]  
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Joe87monteSS Offline
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Joe87monteSS  Offline
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Memphis,TN
If it doesn't shake, I'd leave it alone.


Joey
Engine/head builder/machinist
1987 Monte Carlo SS 383/4 Speed
2004 Silverado
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#919649 - 02/22/12 12:12 PM Re: 383 and balancing????? [Re: Joe87monteSS]  
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Crisco Offline
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Crisco  Offline
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Jacksonville, Florida
It does shake but I also have a big cam in it



1986 SS, 383/200-4r/3.73 Gears

#919687 - 02/22/12 06:38 PM Re: 383 and balancing????? [Re: Crisco]  
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Joe87monteSS Offline
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Joe87monteSS  Offline
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Memphis,TN
So does mine, but it doesn't shake. If its really bothering you to know, I suppose you could pull a front or rear main cap and check the bearing. If its excessively worn, think about changing some things up.

It would also help to now exactly which crank is in there.


Joey
Engine/head builder/machinist
1987 Monte Carlo SS 383/4 Speed
2004 Silverado
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