351 Cleveland harmonic balancer slipped photos

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1971 Mustang Mach 1 M code 351 4 speed
I just pulled the harmonic balancer on my 351 Cleveland as I was having a bad engine vibration above 3,500 RPM and I knew that it had slipped as when I tried to time it, there was no way to get the engine to even stay running with the timing where the balancer said it needed to be. There is not a lot of information out there on this topic and I though I would just put this out there so when people search for info they can find something on the subject. Popular belief is that for this to happen the rubber in the balancer has to look really cracked, bulging and in really bad shape. My old balancer has some cracks on the rubber, but really not something out of the ordinary for an older balancer, and there is really little to no bulging of the rubber, yet it has obviously slipped. The outer ring is on there tight, there is no way that I can move the outer ring no matter how hard I have tried. I put both a new balancer and my old balancer with the keyway at the 12 o'clock position. The old balancer has a white dot on the outer ring where the zero is at, you can see that at about the 9 o'clock position, and the new one has a silver dot on the outer ring where the zero is at at about the 10 o'clock position. It is off about 30 degrees. Never trust an old balancer, even if it does not look bad, mine is dirty, but the rubber is not really that bad. You balancer could be off by a lot less, lets say 10 degrees, and a small difference like that could drive you up the wall trying to figure out why your car does not run well when everything is where it should be...
 

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Thanks for posting the picture. I've had a couple slip over the years and had the outer ring explode once. It was a 7200 RPM thing. Chuck
 
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Thanks for sharing. It's not as much a matter of the rubber degrading as it is about the bond between the rubber and the metal hub and ring. Obviously, when the rubber gets bad enough it will break down and slip, no matter how good the bond is. However, the rubber can still look good and a poor bond give way and the ring will slip.
 
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1972 Mustang convertible, 351C 2V with FMX (#'s matching)
Currently equipped with 351C 4V 4BM, .060 over, roller cam, Sanderson block huggers, -AC

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Joined
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277
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1972 Mustang convertible, 351C 2V with FMX (#'s matching)
Currently equipped with 351C 4V 4BM, .060 over, roller cam, Sanderson block huggers, -AC
When they slip it looks like this!
Either because a “made in china” tappet cam washed out the #2 exhaust valve lobe, or the damper just decided to cash it in and enough was enough.

To me there were no obvious signs of degradation with the “old one” when the previous engine build was going together as it went on as normal and timed in GTG.
I did learn that $100-200 on a new damper is probably a better insurance policy than indexing the “other one” to see if it lets go (yes it did) but the new one was indexed as well.
To me, my silver lining is that it turned me back into a “rock n roller” cam guy because I see investing in a smoother, more durable valve train and most importantly… no more zinc oil to incite a blame game between cam/lifter suppliers that blow you off and blame others…
 

jspears

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I put a dayco "race performance" balancer on my milder engine. I just could not bear to reinstall the original one.
I think I would also go roller cam given a choice again.
 
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