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Discussion Starter #1
Hi, 69 GTO convertible, 1965 Pontiac 421 motor, very well built, brand new performance parts inside and out. While prepping for Spring, i noticed that the bottom pulley (crank) had a wobble to it. You can really notice it. I took off the belt, then removed the pulley assembly, hoping this was the issue.
Running the motor like this for a second, I can still see a very slight wobble on the inside large nut, it is very noticible with the pulley on but you can still surely see it. It is wobbling ~.5cm, not alot, but enough that it not looking very safe and your like "what is going on there"?
I have not idea what is causing this and what to do to figure this out and fix it or troubleshoot it.
Asking for some help on how to approach fixing this.
Thanks in advance. I am heading out to garage, my brother is bringing over a "puller" but we do not know what to look for and going by instinct.
Thanks, Shane
 

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If we make the assumption that you don't have a bent crank (surely not...) then since you see it with the pulleys off it must be the balancer. They do wear out - the rubber elastomer between the inner body and outer ring can deteriorate and allow things to start moving around. It will eventually get loose enough to allow that outer ring to come completely off and get "launched" off the motor and start banging around under the hood... or THROUGH the hood.... obviously it's desirable to avoid this :D

Bear
 

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Discussion Starter #4
Excellent feedback, thanks. I do see a little bit of oil around the seal there. Is this something i could just replace myself? Just pick one from Summit and go for it?

The shop that built the engine (R+R Automotive, Eping NH), is pretty far away from me. I know the crank was balanced at the shop, does this change my thought of replacing the balancer?
Thank you again...Shane
 

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Pontiac cranks are internally balanced so you should be good, all you need is a gear puller to get the old one off. Like rukee said if there are no drill marks in the balancer you should be good.
 

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And yes, you can replace the crank seal on-car. I always do it when the timing cover is on the bench, though. Much easier! Sounds like you need a new harmonic balancer, IMO.
 

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Very common for these old balancers to work loose, crack, and eventually fail. They can destroy the crankshaft if they are run too long. Although I'm running original dampers on both of mine, new dampers are a great idea.
 
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