'67 vs '69 302 harmonic dampers

[69Z28-RS]

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?

[bertfam]

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]

'67-'68 302 balancer photos attached...

Paul

[69Z28-RS]

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...

[JohnZ]

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.

[69Z28-RS]

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?

[bertfam]

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]

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.. 

[woodsman1172]

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]

You're right woodsman, esp if the engine or the parts are 'new' to you..