302 Vibration

Mystang66

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Jul 23, 2011
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I have 302 HO out of a 1985 Mustang in my II. Just recently finished restoring the car. The engine was built with a mild cam, Weiand intake, Holley 4bbl carb, Hedman headers. The transmission and torque converter were just rebuilt a mouth ago and I have a 141 tooth 50 oz imbalance flexplate from Art Carr (CPT) in the car. I just took it into a local mechanic today to dial it in (idle and timing) and he told me he thinks there is too much vibration. He checked the harmonic balancer and it was correct. He thinks it may be the wrong flex plate, but I'm certain thats correct, because I verified it before putting it in. Looking for other suggestions on what it might be. BTW, I just ran a compression check on all cylinders and everything checked out.
 
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LILCBRA

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Is it a possibility that the local mechanic doesn't have experience with older/modified engines and thinks that they run more like newer cars?
 

2Blue2

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It all sounds straight forward enough but...
You say 'out of' an 85, did you check casting number yourself? Could your block have been rebuilt with the 28.2 imbalance crank?
Might need to have whole rotating assembly balanced together.

Motor Trend Quote;

Prior to 1981, production 302s used a 28.2 oz-in imbalance factor. The 1981-and-later production 302 engines, the current Ford Racing 302-based crate engines, and all the late, unlamented 255ci engines have lightweight cranks that require the 50 oz-in imbalance factor. (Caution: There are reports that some rebuilt, remanufactured "service-replacement" 302 engines intended for 1980-and-earlier models—even some sold through Ford Service—were rebuilt using lightweight cranks, which would require a 50 oz-in flywheel and damper.)
 
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Mystang66

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Jul 23, 2011
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Minneapolis, MN
It all sounds straight forward enough but...
You say 'out of' an 85, did you check casting number yourself? Could your block have been rebuilt with the 28.2 imbalance crank?
Might need to have whole rotating assembly balanced together.

Motor Trend Quote;

Prior to 1981, production 302s used a 28.2 oz-in imbalance factor. The 1981-and-later production 302 engines, the current Ford Racing 302-based crate engines, and all the late, unlamented 255ci engines have lightweight cranks that require the 50 oz-in imbalance factor. (Caution: There are reports that some rebuilt, remanufactured "service-replacement" 302 engines intended for 1980-and-earlier models—even some sold through Ford Service—were rebuilt using lightweight cranks, which would require a 50 oz-in flywheel and damper.)
I verified casting while I had it apart. It is possible that someone swapped out the crank to a 28 oz at some point I guess. I never verified the crank part number.
 

Mystang66

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Pictures please.
A7E22753-F660-4762-AEAE-9EA8D823A278.jpeg
 
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LILCBRA

I wish I didn't have all of these balls in the air
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I can't tell you what it would feel like if the wrong flexplate/flywheel and/or balancer were used, I've never experienced it. But I did have a balancer break a long time ago. I don't remember there being funny vibrations per se, but it did feel a lot different for the short drive I had to make with it with nothing attached at the crank. As weird as it may sound, it actually felt a lot more smooth running from what I recall. But that was close to 30 years ago now.... :shrug:
 

2Blue2

will be trying this sex one when I can find it
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Under hood looks clean!
It is possible that someone swapped out the crank to a 28 oz at some point
Alot of the budget crank kits back in the day were based on 28 oz crank

Was just a thought.

Had of a stock harmonic balancer leave my car in the traps at the 1/4 mile.
If it hadn't taken the R. hose with it i might not have noticed till next pass, drove it home.

I've seen a torque converter cause engine vibration, but fresh rebuild right?
 

7991LXnSHO

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I can't tell you what it would feel like if the wrong flexplate/flywheel and/or balancer were used, I've never experienced it. But I did have a balancer break a long time ago. I don't remember there being funny vibrations per se, but it did feel a lot different for the short drive I had to make with it with nothing attached at the crank. As weird as it may sound, it actually felt a lot more smooth running from what I recall. But that was close to 30 years ago now.... :shrug:
I can. The 28 Oz balance flywheel and balancer on a 50 Oz rotating assy shakes a heck of a lot by 3000 rpm. It scares you that it will fly apart.
 
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Mystang66

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Jul 23, 2011
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Minneapolis, MN
Under hood looks clean!

Alot of the budget crank kits back in the day were based on 28 oz crank

Was just a thought.

Had of a stock harmonic balancer leave my car in the traps at the 1/4 mile.
If it hadn't taken the R. hose with it i might not have noticed till next pass, drove it home.

I've seen a torque converter cause engine vibration, but fresh rebuild right?
Yes, fresh rebuild. Maybe only 100 miles on it. I’ve added a video of it running.