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Old 09-27-2013, 06:32 PM   #1
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Harmonic Damper question

Hey guys, I started looking into a vibration issue I have. Even at idle, the engine vibrates noticeably. My guess is either the harmonic balancer or the flywheel counterbalance.

The engine should be a 67 289, and the casting #s I have seen indicate as much (though I haven't checked the block casting behind the starter). I don't know what the trans is, but it's not the C4 it should be...

So the damper is stamped C90E-6316-D2. A google search led me here: http://www.fordsmallblock.com/PDF/e-5.PDF

which says it is counterbalanced, but is for a 69 302. So to my question: both the 67 289 and 69 302 dampers are counterbalanced, but are they interchangeable?

67 A-Code FB GTA

Thanks!
Evan
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Old 09-27-2013, 06:59 PM   #2
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All 289/302/351W prior to 1983 have the same 28 oz. counter balance. In 1983 with the introduction of the 302 H.O. Ford switched to a 50 oz. counter balance. The non-H.O. motors still used a 28 oz.

The balancer you have has the correct counter balance. I would take a very close look at the harmonic balancer to make sure that the counter weight hasn't "free spun". I had this happen to my Cobra. Motor vibrated something crazy.

Good luck.
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Old 09-27-2013, 10:02 PM   #3
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Thanks, that helps out a lot. Would it be obvious if the weight has rotated?

Since the trans isn't original, after this I think the next step is to see what's going on with my flywheel. I know at some point someone put 70s heads on there, maybe when the trans was swapped they put the later flywheel with the different counterbalance on as well. But with the way it is, I don't think the inspection plate is removable without also removing the starter - I have to get a better look.


Evan
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Old 09-28-2013, 10:52 AM   #4
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If it rotated it would be fairly obvious. When mine rotated it moved like 25-30 degrees so it was very obvious. It's possible that's yours may be more subtle. Just inspect very closely. It might even be necessary to remove to get a real good look.
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Old 09-28-2013, 09:25 PM   #5
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Okay, I had a chance to do some digging around, and to remove all doubt, I removed the starter motor to be sure I knew exactly what I was dealing with. Turns out the motor is actually from a 1980 full-size ford. No big surprise as the seller said he had doubts that the engine was original, but as I understand it, this throws a wrench into things.

From what I found, in 80, ford made both a 302 and 255 small block, with the 255 using the 50 oz balance like the 81+ 303s.

Soooooo, my harmonic damper might be okay iffy engine is a 302, but not if it's a 255. I am really curious now what my flywheel balance is (I have to get a socket large enough to turn the crank...I thought I had one somewhere...). Since the engine was able to run and drive halfway decently, I'm guessing both the damper and flywheel aren't incorrect...

So, how does one go about determining if it is a 255 vs a 302?

Thanks,
Evan
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Old 09-28-2013, 09:26 PM   #6
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Oh yeah, that date tag decodes to April 14, 1980...not sure if that helps determine.
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Old 09-29-2013, 08:19 AM   #7
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Please correct me if I found bad info, but it sounds like 289/302 intake will not work on the 1980 255. My intake and water pump are stamped as 67 289, so from what I have read, it is sounding more likely that I have a 302 rather than the dreaded 255. Pulling the intake off should make it clear (or measuring the bore would confirm), but that's a project for later.

I might pose this question to the fox body crowd and see if anyone can provide more info.
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Old 09-29-2013, 12:58 PM   #8
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The 255 shares the same block as the 289/302. Since they are from the same family the 289 intake will bolt right on. Only way to truly confirm if you have a 255 or 302 is to check the crank.
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Old 09-29-2013, 01:47 PM   #9
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Bummer. Checking the bore should do it too, right? Because both the bore and stroke were smaller, right?
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Old 09-29-2013, 01:52 PM   #10
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Correct. The bore for 255 is 3.68" verses 4.00" for the 302. I have to correct myself from earlier as the cranks are the same meaning they both share the 3.00" stroke.
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Old 09-29-2013, 02:28 PM   #11
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Okay, thanks chief, (hopefully) one more question, do you know if the flex plate and damper counterbalance are shared between the two? Since they are the same crank, maybe yes? That would at least get me past the vibration issue regardless of which displacement it has.
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Old 09-29-2013, 10:00 PM   #12
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Yes they are the same. A steady vibration like that is either the harmonic balancer spinning on itself or the flex plate threw a weight. I've seen both happen. Good luck in the troubleshooting process
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Old 09-29-2013, 10:09 PM   #13
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Thanks again, I'll post up my findings when I get the time to dig into it.

Chief, were you aboard ship? Arleigh Burke class?
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Old 09-29-2013, 10:18 PM   #14
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Good insight. And I was on a Burke and fixin to go to another one. Love your car by the way. I am jealous.

Hit me via a PM if you have any questions. I'm an old car junky.
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Old 10-01-2013, 09:09 AM   #15
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Quote:
Originally Posted by aegischief View Post
Love your car by the way. I am jealous.
Thanks! Hopefully over time I can bring it back to good health and make it really enjoyable!
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