Engine 347 stroker vibration

Carlini17

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May 20, 2011
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Bought a 91 foxbody with a 347 stroker, twisted wedge heads and a bunch of other goodies etc. Most of the engine, Trans etc on has 500 miles on it. Problem I'm having is a nice vibration at idle you can feel through the shifter and gets worse when you idea and rev it etc. I'm guessing there's a balance issue. The block he said is internally balanced but that would mean the balancer and flywheel need to be neutral correct? Want some info before I go taking out the Trans etc.
 
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General karthief

wonder how much it would cost to ship you a pair
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Bump. Looking for a direction here please
straight ahead :nice:
but seriously, was the miss there when you bought it?
Pull a plug wire off (one at a time) while idling, use a plug wire tool or a pair of pliers with a good insulated handle, the jult you'll get can be exciting, idle will drop and it will run worse till you get to the one with no spark that one will not change, if all's well there then you may have imbalance issue.
 

Carlini17

Member
May 20, 2011
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First thing I did was check the firing order. New plugs, new distributor, new wires, new coil. Motor mounts look stock and Trans mount I don't know. How would I find out if it's internally balanced or external? I wad going by what he told me since he put it together.
 

7991LXnSHO

wanna catch the space herp
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New components can still misfire due to a number of reasons. Please check it out.

As for the balance, besides seeing the previous owner for the receipts (part numbers and the builder), I’m curious how to determine balance without at least pulling the oil pan.
 

90sickfox

Wasn't a pretty sight...and I've got big hands
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People tend to get internally 0 balanced and rotating assembly balanced mixed up. On my 331 the rods and pistons are scale balanced...then the rotating assembly was balanced to 28oz. imbalance. It wasn't zero balanced...but it was explained to me as being internally balanced.

You can pull the balancer off the engine and take pics of it front and rear. We should be able to find if it's 50oz, 28oz, or 0oz. More than likely it's the " run of the mill " Scat 347 rotating assembly, that should be 28oz., with the wrong 50oz flywheel / flexplate.
 

7991LXnSHO

wanna catch the space herp
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People tend to get internally 0 balanced and rotating assembly balanced mixed up. On my 331 the rods and pistons are scale balanced...then the rotating assembly was balanced to 28oz. imbalance. It wasn't zero balanced...but it was explained to me as being internally balanced.

You can pull the balancer off the engine and take pics of it front and rear. We should be able to find if it's 50oz, 28oz, or 0oz. More than likely it's the " run of the mill " Scat 347 rotating assembly, that should be 28oz., with the wrong 50oz flywheel / flexplate.
So how we tell what the crank is? Should it be marked like cams should be?
 

90sickfox

Wasn't a pretty sight...and I've got big hands
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So how we tell what the crank is? Should it be marked like cams should be?

The only way to tell is to drop the pan. Scat will have their name on the first counter weight and a laser etched part number. The rods also will have part numbers that will help identify size.
 
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7991LXnSHO

wanna catch the space herp
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The only way to tell is to drop the pan. Scat will have their name on the first counter weight and a laser etched part number. The rods also will have part numbers that will help identify size.
That’s what I had in mind, but did not want to say wrong.
I agree that 50 Oz balance parts are likely wrong on a stroker.
From experience, a 28 Oz and 50 Oz parts mismatch will idle, and then shake like nothing else by 2500 RPM. A 50 to 0 external imbalance mismatch should be terrifying.
 
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CarMichael Angelo

my rearend will smell so minty fresh,
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straight ahead :nice:
but seriously, was the miss there when you bought it?
Pull a plug wire off (one at a time) while idling, use a plug wire tool or a pair of pliers with a good insulated handle, the jult you'll get can be exciting, idle will drop and it will run worse till you get to the one with no spark that one will not change, if all's well there then you may have imbalance issue.
Did he say he had a miss? he said he had a vibration. Theres a significant difference between a dead misfire and a rotational vibration…( like the word thud or thump versus buzz). I’m thinking he has a buzz instead of a thump.
 

General karthief

wonder how much it would cost to ship you a pair
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No, mike he didn't say he had a miss but many times a miss is described as a vibration or a vibration ends up being a miss, more likely I meant something other than what I typed.
I do have a little more going on than sitting at the beach bar during happy hour in Puerto Vallarta sipping margaritas although I would join ya in a heartbeat.
enjoy my friend, the real world is right around the corner.
 

manicmechanic007

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I have seen transmissions get replaced because of a engine miss
A real pisser
Had a 96 Taurus at the dealer under warranty that vibrated so bad at freeway speed you could hardly keep it on the road
Guy working on it replaced the wheel bearings Then the cv axles. They had the trans man look at the trans and overhauled the AXOD
I finally got the car but was making the original tech fix it
Had him check the tire balance for the fourth? time. It was out 1/4 ounce (one tire)
Had him spin it again it was out 3 ounces
Had him spin it again it was out 8 ounces
I told him to break down the tire and lets see what's in there
He got so excited he did not wait for all the air to shoot out before hitting the bead ripper
It shot fix a flat all over his ass
Cost 5 grand to fix that one by ,mistake
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
24,028
8,890
203
polk county florida
I have seen transmissions get replaced because of a engine miss
A real pisser
Had a 96 Taurus at the dealer under warranty that vibrated so bad at freeway speed you could hardly keep it on the road
Guy working on it replaced the wheel bearings Then the cv axles. They had the trans man look at the trans and overhauled the AXOD
I finally got the car but was making the original tech fix it
Had him check the tire balance for the fourth? time. It was out 1/4 ounce (one tire)
Had him spin it again it was out 3 ounces
Had him spin it again it was out 8 ounces
I told him to break down the tire and lets see what's in there
He got so excited he did not wait for all the air to shoot out before hitting the bead ripper
It shot fix a flat all over his ass
Cost 5 grand to fix that one by ,mistake
Why 5 grand?
 
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JD1964

there is enough sticking out to grab on to
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I asked if the transmission was automatic or manual because had an experience with a vibration after a transmission change. It was a rebuild automatic transmission and converter. On start up it was vibrating. I scratched my head a few minutes, unbolted the converter from the flex plate and pushed it back towards the transmission a bit. Started it up and the vibration was gone.

I called the supplier and explained. They shipped me a new converter. Problem solved. So obviously, that first converter they sent me was way out of balance.
 
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