Harmonic balancer question 250 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chuck69ss · 03-10-2013, 06:52 PM

I just picked up a 68 GMC and am going through it identifying problems. I was trying to check the timing and noticed that the harmonic balance / pulley rotates several degrees w/o moving the crank. it stops hard and runs well. I can't see a keyway and am only familiar with the SBC style separate balancer pulley arrangement.

I suppose that I need to pull this to see what is going on. Is there a key that isn't visible? Anything else I should know?

Thanks.

Like the forum. Been checking it out.

Tx Firefighter · 03-10-2013, 10:13 PM

Yes there is a woodruff key that indexes the balancer to the crank like you're thinking. There is not, however, a bolt that secures the balancer to the crank. It's just pressed into place.

Often on six cylinders, it's the outer hub on the balancer that is slipping on the inner hub due to the rubber being deteoriated. The outer hub being the pulley also makes it under a lot of strain compared to engines with bolt on pulleys. It's just the character of the beast on those engines.
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chuck69ss · 03-10-2013, 10:20 PM

Thanks. It definately is spinning on the crank. The balancer seems to be pretty solid. Seems like maybe the key sheared but odd that it doesn't spin completely.
There is some grime too. Probably a good time to change the timing cover seal,while I'm in there.
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Husker · 03-10-2013, 10:24 PM

My 68 has a 250, when I went to pull off the balancer it just come off. No puller just loose. I replaced it
Ron

chuck69ss · 03-13-2013, 11:34 AM

Well I too it off. The balancer and key are definitely worn. Not sure about the crank though. I heard that a previous owner added power steering, and I'm thinking that he used an old balancer to add the 2nd belt.

PanelDeland · 03-13-2013, 03:35 PM

From the pic,it looks like the rubber connecting the two hubs(inner and outer) is shot.I would look for a new one.

Tx Firefighter · 03-13-2013, 06:07 PM

I'd get a new woodruff key and see if it fits pretty snug in the crank before I went any further. If it fits moderately well, a new balancer is definitely in order. They still sell them, reasonably priced. Also fix your oil leak so the new balancer doesn't get soaked and deteoriate the rubber leaving you with the same issue down the road again.
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03-10-2013, 06:52 PM	#1
chuck69ss Registered User Join Date: Dec 2012 Location: Pascoag, RI Posts: 33	Harmonic balancer question 250 I just picked up a 68 GMC and am going through it identifying problems. I was trying to check the timing and noticed that the harmonic balance / pulley rotates several degrees w/o moving the crank. it stops hard and runs well. I can't see a keyway and am only familiar with the SBC style separate balancer pulley arrangement. I suppose that I need to pull this to see what is going on. Is there a key that isn't visible? Anything else I should know? Thanks. Like the forum. Been checking it out. __________________ '68 GMC C1500 (CS10) LWB Wideside. Restoring a '69 Camaro, (also have an '06 Mustang.)

03-10-2013, 10:13 PM	#2
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Harmonic balancer question 250 Yes there is a woodruff key that indexes the balancer to the crank like you're thinking. There is not, however, a bolt that secures the balancer to the crank. It's just pressed into place. Often on six cylinders, it's the outer hub on the balancer that is slipping on the inner hub due to the rubber being deteoriated. The outer hub being the pulley also makes it under a lot of strain compared to engines with bolt on pulleys. It's just the character of the beast on those engines. Posted via Mobile Device

03-10-2013, 10:20 PM	#3
chuck69ss Registered User Join Date: Dec 2012 Location: Pascoag, RI Posts: 33	Re: Harmonic balancer question 250 Thanks. It definately is spinning on the crank. The balancer seems to be pretty solid. Seems like maybe the key sheared but odd that it doesn't spin completely. There is some grime too. Probably a good time to change the timing cover seal,while I'm in there. Posted via Mobile Device __________________ '68 GMC C1500 (CS10) LWB Wideside. Restoring a '69 Camaro, (also have an '06 Mustang.)

03-10-2013, 10:24 PM	#4
Husker Registered User Join Date: Dec 1999 Location: Mid NE USA Posts: 2,212	Re: Harmonic balancer question 250 My 68 has a 250, when I went to pull off the balancer it just come off. No puller just loose. I replaced it Ron __________________ Member #111 68 C-10 Daily Driver 70 4x4 Project 76 Jeep CJ-5 Help Support the Board: http://67-72chevytrucks.com/vboard/payments.php He who knows nothing is closer to the truth than he whose mind is filled with falsehoods and errors. Thomas Jefferson

03-13-2013, 11:34 AM	#5
chuck69ss Registered User Join Date: Dec 2012 Location: Pascoag, RI Posts: 33	Re: Harmonic balancer question 250 Well I too it off. The balancer and key are definitely worn. Not sure about the crank though. I heard that a previous owner added power steering, and I'm thinking that he used an old balancer to add the 2nd belt. __________________ '68 GMC C1500 (CS10) LWB Wideside. Restoring a '69 Camaro, (also have an '06 Mustang.)

03-13-2013, 03:35 PM	#6
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: Harmonic balancer question 250 From the pic,it looks like the rubber connecting the two hubs(inner and outer) is shot.I would look for a new one. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

03-13-2013, 06:07 PM	#7
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Harmonic balancer question 250 I'd get a new woodruff key and see if it fits pretty snug in the crank before I went any further. If it fits moderately well, a new balancer is definitely in order. They still sell them, reasonably priced. Also fix your oil leak so the new balancer doesn't get soaked and deteoriate the rubber leaving you with the same issue down the road again. Posted via Mobile Device



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