Help: Weird Timing Mark Location - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Miles · 02-14-2006, 06:26 PM

Here’s a problem that has me stumped – any helpful info would be appreciated.

I had a 350ci crate engine put in my ’72 C-10 about a year ago and it has been running really well since. When I went to tune it up recently, I found that the timing was set at about 16 before TDC (manual transmission; I’ve been setting the timing at 8 before for the last 20 years with no problems!).

The distributor had not been messed with as far as I can tell, but I went ahead and had a local mechanic switch me over to electronic ignition. He timed the engine ‘by ear’ and found the timing mark to be around 18 before TDC when done. He told me that he checked to verify that when cylinder #1 is at TDC that the timing mark was at zero.

One thing I thought could be going on (however unlikely) is that the harmonic balance/damper may be defective – perhaps there has been slippage of the bonding elastomer connecting the inner-outer pieces which resulted in a mis-located mark? I thought I would see what other folks thought before removing the harmonic balance to check its alignment this since the part is only a year old and I assume it is OK.

I am a bit out of my league on this, so if there is more info needed, please direct me to what additional info you may need to track this issue down/clarify what’s going on.

Thanks in advance!

Miles

mjrmn · 02-14-2006, 08:31 PM

I think you may be right on the money with the idea of the outer ring of the balancer shifting. This can easily happen with new balancers or old. Especially if they are really revved up. Also may want to check with the engine supplier/installer to see if they have had similar problems with other engines they have done.
Good Luck!!
Mike

**68 Stepside** · 02-14-2006, 08:44 PM

I had a ZZ3 crate engine from GM in my 85 Z28, the balancer slipped on it, after less than 3,000 miles. I think you may be right on the money as well.

jimfulco · 02-14-2006, 10:23 PM

Didn't they change the timing mark location by about 10 degrees sometime around the early '70s?

jhow66 · 02-15-2006, 12:50 AM

Was this with advance hose on or off?

al's71gmc · 02-15-2006, 01:03 AM

With the electronic ignition I thought you were supposed to set it at 12 before tdc? I read that somewhere??

**VetteVet** · 02-15-2006, 01:11 AM

You need to go back to basics on the tune-up before getting too far off base.
What was the idle rpms when you checked it they should be set at 600 or near. Was the idle rpm set with a vacuum gauge and like Jhow said did you have the vacuum hose off the distributer and plugged .
If your mechanic said number 1 was at top dead center and the timing mark was on zero, what makes you think the outer ring has slipped?

02-14-2006, 08:31 PM	#2
mjrmn '67 K10 Work In Process Join Date: Feb 2004 Location: Delano MN Posts: 163	Re: Help: Weird Timing Mark Location I think you may be right on the money with the idea of the outer ring of the balancer shifting. This can easily happen with new balancers or old. Especially if they are really revved up. Also may want to check with the engine supplier/installer to see if they have had similar problems with other engines they have done. Good Luck!! Mike

02-14-2006, 08:44 PM	#3
68 Stepside huh? Join Date: May 2000 Location: Washington, Illinois Posts: 5,692	Re: Help: Weird Timing Mark Location I had a ZZ3 crate engine from GM in my 85 Z28, the balancer slipped on it, after less than 3,000 miles. I think you may be right on the money as well. __________________ Someday when I'm lonely, Wishing you weren't so far away, Then I will remember Things we said today. RIP El Jay

02-14-2006, 10:23 PM	#4
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Re: Help: Weird Timing Mark Location Didn't they change the timing mark location by about 10 degrees sometime around the early '70s?

02-15-2006, 12:50 AM	#5
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Help: Weird Timing Mark Location Was this with advance hose on or off? __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

02-15-2006, 01:03 AM	#6
al's71gmc 4 eyed fever Join Date: Jul 2005 Location: Eureka, Nevada Posts: 500	Re: Help: Weird Timing Mark Location With the electronic ignition I thought you were supposed to set it at 12 before tdc? I read that somewhere?? __________________ 1971 GMC 2500 4x4 1972 GMC Sierra Grande 1/2 t 4x4-#1 son's truck. Recently completed resto. 4 YO daughter," Daddy, I like your truck better than Mom's." (2000 F350-ranch truck) Smart kid!!

02-14-2006, 06:26 PM	#1
Miles Registered User Join Date: Feb 2006 Location: Oklahoma Posts: 3	Help: Weird Timing Mark Location Here’s a problem that has me stumped – any helpful info would be appreciated. I had a 350ci crate engine put in my ’72 C-10 about a year ago and it has been running really well since. When I went to tune it up recently, I found that the timing was set at about 16 before TDC (manual transmission; I’ve been setting the timing at 8 before for the last 20 years with no problems!). The distributor had not been messed with as far as I can tell, but I went ahead and had a local mechanic switch me over to electronic ignition. He timed the engine ‘by ear’ and found the timing mark to be around 18 before TDC when done. He told me that he checked to verify that when cylinder #1 is at TDC that the timing mark was at zero. One thing I thought could be going on (however unlikely) is that the harmonic balance/damper may be defective – perhaps there has been slippage of the bonding elastomer connecting the inner-outer pieces which resulted in a mis-located mark? I thought I would see what other folks thought before removing the harmonic balance to check its alignment this since the part is only a year old and I assume it is OK. I am a bit out of my league on this, so if there is more info needed, please direct me to what additional info you may need to track this issue down/clarify what’s going on. Thanks in advance! Miles __________________ 1972 Chevy C-10

02-15-2006, 01:11 AM	#7
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,709	Re: Help: Weird Timing Mark Location You need to go back to basics on the tune-up before getting too far off base. What was the idle rpms when you checked it they should be set at 600 or near. Was the idle rpm set with a vacuum gauge and like Jhow said did you have the vacuum hose off the distributer and plugged . If your mechanic said number 1 was at top dead center and the timing mark was on zero, what makes you think the outer ring has slipped? __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.



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