Crank pulley and harmonic balancer - Team Camaro Tech
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post #1 of 6 (permalink) Old Jul 26th, 14, 11:30 AM Thread Starter
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Scott
 
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Crank pulley and harmonic balancer

Not sure if this as an issue or not. 1968 BB396, M20.
I changed crank pulley from single groove to double groove to add AC.
I used billet specialties billet aluminium pulley from Summit. After install looked like a pretty good wobble on crank pulley. Pulled back off, watched just balancer to see it wobbled. Appeared to move slightly back and forth but hard to tell.
Put old pulley back on and watched again could see lil wobble again but not as noticeable as with larger 2 groove pulley. How ever did notice when I reved the motor the wobble went away and it spun true.

Is this normal? Does crank pulley wobble at low RPM idle and balance out and smooth out under RPM?

Would it be ok to put new pulley back on? Or does it sound like I need a new harmonic balancer??

Not exactly sure how balancer is suppose to work to self balance, maybe wobble is normal till certain Rpm is achieved???
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post #2 of 6 (permalink) Old Jul 26th, 14, 12:13 PM
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Fred
 
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Re: Crank pulley and harmonic balancer

A balancer is really a harmonic cancellation device. The outer rig is tuned to cancel the drone that the crankshaft produces in normal operation. In your minds eye visualize the operating crankshaft from the side. Erase all the needless stuff like the block, pistons and rods. Notice that the power from the forward rod journals has only one way to get to the flywheel. It's via all the other journals. That creates twist and thusly harmonics that will destroy the crank without a dampener.
So, to answer your question, the balancers job is not to balance itself. It has to be balanced already or you've got big problems. The outer ring is pressed to an inner hub and held in place via an elasticizer. It could be that the ring is no longer true to the hub. But your pulley is not mounted to the ring anyway. If the pulley is not true it'll be more noticible at low speed and appear to cancel out when the engine is rev'd.
So,,,, if it's a new pulley, I'd just run it. This is so much fun.

One owner 69 Camaro,(yep, bought it new
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post #3 of 6 (permalink) Old Jul 26th, 14, 01:26 PM Thread Starter
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Scott
 
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Re: Crank pulley and harmonic balancer

Ok Fred. I'm confused. So u said run it, but ya think center ring might be out of whack or the pulley is not true?
Shouldn't I send the pulley back? It's brand new and supposedly precision balanced for motors upto 1000hp.
If the damper ring is worn, shoud I not replace harmonic balancer?
My fear is wearing out crank bearings due to vibrations???
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post #4 of 6 (permalink) Old Jul 26th, 14, 02:42 PM
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Fred
 
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Re: Crank pulley and harmonic balancer

I confused myself too.
OK, I'm feeling much better now. Yeah, get a different pulley and change the balancer. Can't hurt.
Did I ever tell you my SFI ATI balancer story? It's ugly.
When my car had to have a super dupper balancer (<11.50ets) I installed an ATI with magnets for a crank trigger. About the second weekend when pulling to the bleach box, the balancer FELL OFF! The hub mounting bolts that hold it together sheered. It dented up my original crank pulley too. I was not pleased, especially because this failed balancer was suppose to be so much better than my original, still perfect balancer . Grrrrr.
Well, the balancer got replaced and the pulley was saved. This is so much fun.

One owner 69 Camaro,(yep, bought it new
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All with 1960's stuff. (except tires and converter)
+ MT Super Scavenger headers & 3" full exhaust with X pipe. 3700 lbs. with me in it.
1000cfm AED and HD Harold-Lunati SR, 725 lift with shaft rockers too.
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post #5 of 6 (permalink) Old Jul 26th, 14, 04:54 PM
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Anne
 
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Re: Crank pulley and harmonic balancer

Quote:
Originally Posted by PhantomRider View Post
I changed crank pulley from single groove to double groove to add AC.
Unless you don't have power steering, won't you need a 3 groove crankshaft pulley for an AC equipped car ?

I know I had to have a 3 groove type and it wasn't easy to find a stock one. Actually the 3 groove pulley is a 2 groove with a bolt-on extension.

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post #6 of 6 (permalink) Old Jul 27th, 14, 07:31 AM Thread Starter
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Scott
 
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Re: Crank pulley and harmonic balancer

Thanks Fred, yep the so called best parts are not always the case. Spent the extra money as to not run into this issue, but Murphy's law.

Yes Anne, u are correct. My car is manual steering, so 2 groove. If it was power plus AC then I would have needed a 3 groove.
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