Author Topic: '67 vs '69 302 harmonic dampers  (Read 2311 times)

69Z28-RS

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'67 vs '69 302 harmonic dampers
« on: February 19, 2013, 06:18:16 PM »
in digging thru my parts, trying to find all the '69 parts to put my 302 back together, I found a couple of seemingly appropriate harmonic dampers, but there are some differences.   I have identified the '69 302 damper, since I stamped my initials on it when I rebuilt the engine back in the mid 70's, and had the machine shop add grooves at 30, 90, 180, and 270.  It's stamped on the front '7708', which I believe I've read is correct for the '69 Z28.
The other large damper I had, which I believe to be from the '67 302 which I disassembled once upon a time.. :)    It only has a '1' and a '7' on the front (see photo).  but I also noticed the keyway vs TDC is not the same as for the '69 damper.   Is one of these weights 'slipped'?  or is there supposed to be a keyway difference?  and if so, why?   If so, I assume the crankshaft keyways are also appropriately different?  Can someone point me to a document that clarifies this?  or perhaps provide clarification here?
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

Ed_B

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Re: '67 vs '69 302 harmonic dampers
« Reply #1 on: February 19, 2013, 10:47:32 PM »
I don't see a picture, but the timing mark on 1968 and earlier balancers is in line with the crankshaft keyway. In 1969, the timing mark was rotated about 10 to 12 degrees toward the Advance (A) mark.

Ed

1968RSZ28

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Re: '67 vs '69 302 harmonic dampers
« Reply #2 on: February 19, 2013, 11:21:46 PM »
'67-'68 302 balancer photos attached...

Paul

69Z28-RS

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Re: '67 vs '69 302 harmonic dampers
« Reply #3 on: February 20, 2013, 01:21:40 AM »
I don't see a picture, but the timing mark on 1968 and earlier balancers is in line with the crankshaft keyway. In 1969, the timing mark was rotated about 10 to 12 degrees toward the Advance (A) mark.
Ed

Thanks Ed,  the keyway to TDC relationships  you describe are consistent wtih the '67 and '69 balancers I have.   The '67 is pictured on the left wtih the '69 on the right.   The '69 has the 7708 stamping, while the '67 has a '1' and a '7', although the numbers appear to be inverted to one another?    What is the coding on a '67 supposed to be?   Both balancers appear to have similar cast in 'codes' on the rear inside...
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

JohnZ

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Re: '67 vs '69 302 harmonic dampers
« Reply #4 on: February 20, 2013, 04:32:14 PM »
Thanks Ed,  the keyway to TDC relationships  you describe are consistent wtih the '67 and '69 balancers I have.   The '67 is pictured on the left wtih the '69 on the right.   The '69 has the 7708 stamping, while the '67 has a '1' and a '7', although the numbers appear to be inverted to one another?    What is the coding on a '67 supposed to be?   Both balancers appear to have similar cast in 'codes' on the rear inside...


The only difference between those two balancers is the part number and the location of the timing index line on the inertia weight relative to the hub keyway; photo below shows the different '68 and earlier and '69 index line locations.
'69 Z/28
Fathom Green
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69Z28-RS

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Re: '67 vs '69 302 harmonic dampers
« Reply #5 on: February 20, 2013, 06:00:25 PM »
John,  I'm sure Chevrolet had some reason for changing the keyway / TDC index marking between '68 and '69, but it's not obviuos why they did so??    Can you shed some light on that?
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

Ed_B

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Re: '67 vs '69 302 harmonic dampers
« Reply #6 on: February 20, 2013, 07:02:44 PM »
Quote
John,  I'm sure Chevrolet had some reason for changing the keyway / TDC index marking between '68 and '69, but it's not obviuos why they did so??    Can you shed some light on that?

I'll let John elaborate, but the short and sweet is because of the move from the short water pump to the long water pump, and the relocation of the alternator to the passenger side of the car. Moving the timing mark made it easier to read the timing.

Ed

69Z28-RS

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Re: '67 vs '69 302 harmonic dampers
« Reply #7 on: February 20, 2013, 07:14:19 PM »
thanks Ed,  I KNEW there had to  be a reason.. and that one makes sense!.... but it can put a whack into checking timing if you have an inconsistent mix of parts..  :)
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

woodsman1172

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Re: '67 vs '69 302 harmonic dampers
« Reply #8 on: February 21, 2013, 08:55:58 AM »
Always a good idea to determine TDC via piston feel or gauge, unless (or until) you have verified the timing mark on your dampener is correct.

69Z28-RS

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Re: '67 vs '69 302 harmonic dampers
« Reply #9 on: February 21, 2013, 01:54:05 PM »
You're right woodsman, esp if the engine or the parts are 'new' to you.. :)   
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan