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Discussion Starter #1
I have a 383 stroker in my 79 installed by PO. I noticed that I have a vibration at 1500 RPM. Nothing awful but noticeable. I assume the 383 is externally balanced. The flexplate has a weight but the balancer appears to be of the neutral type. Question is whether I have an incorrect flexplate or balancer/damper. If this stroker is truly externally balanced then it would be the incorrect harmonic balancer. If it’s internal balance then the flexplate shouldn’t have the weight and it need to be changed Bottom line is balancer and flexplate should match. Opinions on my line of thinking?
 

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I have a 383 stroker in my 79 installed by PO. I noticed that I have a vibration at 1500 RPM. Nothing awful but noticeable. I assume the 383 is externally balanced. The flexplate has a weight but the balancer appears to be of the neutral type. Question is whether I have an incorrect flexplate or balancer/damper. If this stroker is truly externally balanced then it would be the incorrect harmonic balancer. If it’s internal balance then the flexplate shouldn’t have the weight and it need to be changed Bottom line is balancer and flexplate should match. Opinions on my line of thinking?
I'll be following this out of curiosity. Don't have anything definitive for you but I think if you had the wrong flexplate it WOULD be awful. I had a 347 Ford stroker that also had a vibration that wasn't awful. Maybe the rotating assembly wasn't properly balanced or maybe the flexplate wasn't weighted correctly.
 

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Just FYI
base 305s and 350s and HO's from 86/87 till the LS motors,
and 93up LT1s, were both internal and external balance..
Internal Front/External Rear,, due to the 1-piece rear seal/flexplate design...
.
MZ
is the vibration when moving too, or stopped and just at a fast idle??
.
do you know anything else about the motor??
1-piece or 2-piece rear seal??
what crank kit or rotating assy. ??
was the motor balanced??
is it really a 383?? or what ??
.
couple things to check
is if the flexplate was put on correctly,
is it lined up with the dowel hole, [some cranks have the dowel, a-lot don't ] ..
does the torqconverter fit the crank pilot/line-up hole??
 

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never say never
base 305s and 350s and HO's from 86/87 till the LS motors,
and 93up LT1s, were both internal and external balance..
Internal Front/External Rear,, due to the 1-piece rear seal/flexplate design...
.

[/QUOTE]
 

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long time ago,, far, far away.....
I was sold a new 454BBC flexplate for a 400SBC..
turns out the 454 has a bigger weight, and
the whole car jumped up and down at idle ~800rpm..
it wasn't too bad in gear or driving,
it wasn't a violent vibration, but it was very annoying...
a new 400sbc flexplate fixed it..
this wasn't a rebuild,
just a quickie hone, re-ring, bearings, cam/lifters,
ported/milled heads, drove it hard for 2yrs,
shifted at 7500, and all was well,
till the trans quit the job...
 

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Discussion Starter #7
[QUOTE
If the flexplate has a weight, the harmonic balancer should also have the imbalanced shape.
never say never
base 305s and 350s and HO's from 86/87 till the LS motors,
and 93up LT1s, were both internal and external balance..
Internal Front/External Rear,, due to the 1-piece rear seal/flexplate design...
.
MZ
is the vibration when moving too, or stopped and just at a fast idle??
.
do you know anything else about the motor??
1-piece or 2-piece rear seal??
what crank kit or rotating assy. ??
was the motor balanced??
is it really a 383?? or what ??
.
couple things to check
is if the flexplate was put on correctly,
is it lined up with the dowel hole, [some cranks have the dowel, a-lot don't ] ..
does the torqconverter fit the crank pilot/line-up hole??
[/QUOTE]

Its difficult trying to determine which type of balance I have based on all the different set ups available today. It could be any multitude of set ups. So trial and error is what was decided. I am swapping out the high stall converter anyway. So tranny was pulled. Problem number 1, Flexplate was not lined up on the dowel hole. A New non weighted flexplate was installed and tried to rule that out. Ran engine vibe still there. Old FP reinstalled and lined up on dowel hole. Still have vibe. A notched 400 type balancer was installed.There lies problem #2- incorrect balancer. Vibe is gone and purrs through the RPM ranges. So I have a unbalanced set up that requires both ends to have weighted components. One item to note was since crank didn't have a dowel and just a hole, it left installer with option to install incorrectly.

So expecting to get some added HP and can already feel extra power on the pedal. May put on a DYNO to see what the results are.

I tried hard but I couldn't get any info at all from the PO / builder as he will not answer me and now I think I know why. It sucks when you don't have documentation. A future consideration when purchasing another person's build

Seems like problems are solved but still need road test. Thanks for the advice and comments. I hope this will help others in the future.
 

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WTG MZ for figuring it out, that was quick..
sometimes trial and error works on the 1st and 2nd time..
x2 on the number of combinations to consider, and deal with..
.
did you double check the Timing/Mark and Tab to
make sure its still on TDC for timing adjustments..
 

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Discussion Starter #9
WTG MZ for figuring it out, that was quick..
sometimes trial and error works on the 1st and 2nd time..
x2 on the number of combinations to consider, and deal with..
.
did you double check the Timing/Mark and Tab to
make sure its still on TDC for timing adjustments..
Car was put on dyno and tuned and now has 366 HP at rear wheels running like a beast
127172

Thanks
 
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