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383 balance

2K views 21 replies 8 participants last post by  funbiz99 
#1 ·
not sure what happend to my first post....anyhow i have a 383 the flexplate has a weigh bolted on it but the balancer has no weights. is this internal or external balanced?? is this some kind of hybrid lol?
 
#3 ·
if its a 383 then it has a 400 crank and therefore it is externally balanced and furthermore will be weighted externally

the balancer wont have weight attached to it, rather it has an area of removed material on the backside, as seen here on my 400 engine:


unless someone knows something different ?

here is stock factory 400 external balance weight:



good luck
 
#4 ·
ok this is why i am still confused! there is suppose to be a forgrd scat crank. there is no material removed from the harmonic tomorrow i will post a pic. the flywheel weight does not look like it is factory installed. should i put a 400 harmonic balancer on it? i already ordered it before i noticed it was not weighted. thanks
 
#9 ·
funbiz99 said:
i agree that is what the post is about........but what is the best course of action?
My guess is if it is a scat crank and still has the flex plate and balancer from a 350 it was never balanced from the git go , externally or other wise. I believe the weights in the balancer are removed for a internally balanced engine and some are even adjustable.
 
#10 ·
ok then should i just put a 400 balancer&flexplate on? the engine seems to run smooth (no noticeable vibration) , if i wasn't underneath changing the exhaust i would have never noticed the weight held in by a bolt on the flexplate. at first glance i thought it was a spacer until closer inspection!
 
#11 ·
There are 2 versions of the 383 build. One uses a 2-piece rear main seal crank and the other uses the later 1-piece rear main seal. The first one uses a flywheel AND balancer that are weighted. The second uses a weighted flywheel but the balancer is neutral.

The 1-piece rear main seal SBC's came out in 1985.

If you have the 1-piece rear main combo, then the balancer should not be weighted (aftermarket balancer) or have material removed from the backside (OEM balancer).

tom
 
#14 ·
Richard H. said:
My guess is if it is a scat crank and still has the flex plate and balancer from a 350 it was never balanced from the git go , externally or other wise. I believe the weights in the balancer are removed for a internally balanced engine and some are even adjustable.
If it were an untouched Scat crank it would probably shake like a working girl in a confessional.

tom
 
#15 ·
funbiz99 said:
ok this is why i am still confused! there is suppose to be a forgrd scat crank. there is no material removed from the harmonic tomorrow i will post a pic. the flywheel weight does not look like it is factory installed. should i put a 400 harmonic balancer on it? i already ordered it before i noticed it was not weighted. thanks
Good, I'd sure like to see the weight on the flywheel.

Is it a stock balancer or aftermarket?

tom
 
#17 ·
funbiz99 said:
i will upload a pic tonight. i guess the reason im worried is if the balancer is not correct then wont it shorten the life of everythig from not dampening correctly?
It will shorten the life by not BALANCING correctly. Think of it as a tire that has thrown it's balancing weight. When you drive down the road, it goes whomp, whomp, whomp.

Your rotating assembly will do the same thing if not properly balanced. The only difference is that your rotating assembly makes a different sound - one best described as $100 bills being placed into the hands of your machinist... :p

Keep in mind that some of the externally balanced AFTERMARKET balancers move the weight to the inner ring - not the outer ring. This prevents damage to the engine if the outer ring slips... It may be hard to see the weights if this is the case...
 
#18 ·
ok i have the answer..............i see a lot of posts where u never hear the end result. come to find out i have a one piece rear seal block and a internal balanced forged crank. the front is internally balanced and the rear externally balanced. i verified this with scat.
 
#19 ·
funbiz99 said:
ok i have the answer..............i see a lot of posts where u never hear the end result. come to find out i have a one piece rear seal block and a internal balanced forged crank. the front is internally balanced and the rear externally balanced. i verified this with scat.
So that would be an external balanced rear and a neutral front.
That doesn't seem to qualify as an internal balanced crankshaft, just a half-bugger.
 
#21 ·
hi i have a 1990 chevy 305 and iv heard that 86 and later that the motors are external balanced and have a one peice rear main seal which mine does my question is what will happen if the motor has a internal balanced flex plate on it what kind of damage am i lookin at the engine has 3400 miles on it and i just found out that it might be the wrong flexplate but the plate that is on there has a good size balance weight that doesnt look like it would be small enough to balance just the flexplate itself but iv ben told it was internal balance but iv seen the same exact flexplate with the same wieght for external applications some help on this would be so great im loosing my mind on this one
 
#22 ·
first of all is your engine vibrating?? this was complicated for me but i think i have the correct answers.....the one piece rear main seal have a neutral damper and weighted flex plate.....

the problem i had is the fool that did my engine work put some phony CAT crankshaft in totally internal balance one piece....they dont make a flexolate for that....i had to take a weighted plate and remove the weight ***!!! anyhow if your not shaking your probably ok!!!!!!!
 
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