bottom engine pulley wobble? - Pontiac GTO Forum
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post #1 of 8 (permalink) Old 04-10-2013, 09:59 AM Thread Starter
 
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bottom engine pulley wobble?

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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post #2 of 8 (permalink) Old 04-10-2013, 10:34 AM
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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

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post #3 of 8 (permalink) Old 04-10-2013, 10:44 AM
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If the motor has been balanced you may want to take the old and new balancer back to the machine shop so it can be rebalanced. If there are no dill marks on the old one you're probably good to go just bolting it up.
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post #4 of 8 (permalink) Old 04-10-2013, 11:37 AM Thread Starter
 
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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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post #5 of 8 (permalink) Old 04-10-2013, 03:38 PM
 
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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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post #6 of 8 (permalink) Old 04-10-2013, 06:27 PM
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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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post #7 of 8 (permalink) Old 04-11-2013, 08:51 AM
 
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When I rebuilt my 65 389 I bought a brand new balancer from Damper Doctor, price was about $200 for a direct OE replacement.
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post #8 of 8 (permalink) Old 04-11-2013, 12:29 PM
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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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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Complete Engine Compartment Discussion

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