69 Z28 Crankshaft number

[1968RSZ28]

So do we know what the difference between cranks is?

Per Jerry MacNeish's '69 Z/28 Fact Book...

"The 1969 302 crankshaft (part number 3941176) is identical to the one used in the 1968 model year (large journal).  This is a tuftrided forged-steel crankshaft."

Paul

[67rs/ss350 68z/28]

So do we know what the difference between cranks is?

Per Jerry MacNeish's '69 Z/28 Fact Book...

"The 1969 302 crankshaft (part number 3941176) is identical to the one used in the 1968 model year (large journal).  This is a tuftrided forged-steel crankshaft."

Paul

Does that mean a 3279 crank is the same as a 1178?? Keyway and all? And Just different balancers and timing chain covers???

[69Z28-RS]

I was thinking that the 'tufftriding' for '1969 might be the difference in the crankshafts...  Was the '68 PN tufftrided??

[1968RSZ28]

Does that mean a 3279 crank is the same as a 1178?? Keyway and all? And Just different balancers and timing chain covers???

Yes.

Paul

[1968RSZ28]

I was thinking that the 'tufftriding' for '1969 might be the difference in the crankshafts...  Was the '68 PN tufftrided??

Yes.

Paul

[jdv69z]

So when we say casting no is 1178, what does that mean? Is the crankshaft first a steel casting with the number 1178 cast in, then forged, then the journals, etc. machined, and then  tufftrided? Is that how it is manufactured?

There must have been some reason for the part no. change? Could the material spec have been changed?

[miket1]

If I understand the change, and the reason correctly, then the crankshaft keyway itself is likely NOT different from '68 to '69, but instead the timing MARK on the damper, along with the position of the Timing Index (on the timing cover) are rotated slightly (10 deg or so) in order to be more visible and easier to see/adjust the timing.   If I'm not understanding this correctly even now, someone PLEASE correct me explicity ..    If that is correct, then it would be the damper and the timing cover that 'go together'.. with the crank keyway position being consistent over the years.
[/quote]

I'm glad you brought this up about timing, it has the  69 style ,#7708 Balancer and timing cover setup, w/offset timing mark, so, is the crank  keyway  the same from 68 to 69 crankshaft, if so then timing will be correct with these parts.
I may need to call Jerry M. to be sure.

[69Z28-RS]

If I understand the change, and the reason correctly, then the crankshaft keyway itself is likely NOT different from '68 to '69, but instead the timing MARK on the damper, along with the position of the Timing Index (on the timing cover) are rotated slightly (10 deg or so) in order to be more visible and easier to see/adjust the timing.   If I'm not understanding this correctly even now, someone PLEASE correct me explicity ..    If that is correct, then it would be the damper and the timing cover that 'go together'.. with the crank keyway position being consistent over the years.

I'm glad you brought this up about timing, it has the  69 style ,#7708 Balancer and timing cover setup, w/offset timing mark, so, is the crank  keyway  the same from 68 to 69 crankshaft, if so then timing will be correct with these parts.
I may need to call Jerry M. to be sure.
[/quote]

Confirmation never hurts, you could certainly confirm the statement from his book saying that the '68 and '69 crankshafts were the same, AND ask him if he's ever heard of an early '69 Z28 with a '68 crankshaft in it (and find out if Jerry M thinks there would be any issues with this).
.. and bottom line, IF you believe the crankshaft *might* have been installed in the factory, and absent any indicators that indicated the engine had been apart or rebuilt over the years, I would NOT change the crankshaft to a '69 pn...   

[bcmiller]

Jerry said it is possible, but when asked at that time we did not know the engine assembly date. I asked him again.

I don't really know.  I would say quite possible in a September assembly, but more doubtful by early October.  

Pistons are standard?  Bearings look original?

[69Z28-RS]

Jerry said it is possible, but when asked at that time we did not know the engine assembly date. I asked him again.

I don't really know.  I would say quite possible in a September assembly, but more doubtful by early October. 

Pistons are standard?  Bearings look original?

If I recall correctly, if an original assembly, the bearings should also be GM bearings, and would have GM part numbers on the backs...   If someone were replacing the crankshaft (for whatever reason), they would not likely use GM bearings...

[miket1]

I got time to check the crank today, is has been turned .010-.010  w/Clevite  Bearings that look great, I'm just curious as to how this Crank is in the engine and why, I see no reason for someone to just change a Crankshaft  unless they spun a bearing long ago and really damaged it, but doesn't seem normal to install  something different than what it was built with, if it was built with an 1178 Crank, one would think  the same part would be used.
  I can understand going thru an engine to freshen it with new rings, bearings, turn the crank etc.,  so I am thinking they freshened up what they had and assembled it., who knows,  I have seen a lot of mismatched parts from cars built back then, I know if a certain part was not immediately available the assembly line did not stop to wait on it, they used  what was immediately available. 

[bcmiller]

Mike, those 302s were the "hot ticket" in certain dirt track stock cars in the 70s.  They saw a lot of abuse.  Usually came from cars that were wrecked.

Parts were parts. If they worked, they were used.  Running on dirt is REALLY hard on engines.

[bcmiller]

Dad and I had a DZ 302 that was from a dirt track sprint car.  Crankshaft thrust was worn when we got it.  It was OK for a while with new bearings and was generally only run 1/4 mile at a time after that after we put it in a 67 Camaro drag car around 1978 or 79.  

We would swap the 302 in and out with an L78.  Both ran similar times by the way with an M21, 4.88 gears and slicks.  Eventually the thrust on the crank got so worn that it needed to be welded up and repaired.  Rather than doing that we dumped it - and ran only the L78 in the car after that. 

Several years later the car got a 406 small block and was sold.  Should have kept that car. We made side exit exhaust for it from 3 inch tubing.

[miket1]

So do we know what the difference between cranks is?
[/quote]

Per Jerry MacNeish's '69 Z/28 Fact Book...

"The 1969 302 crankshaft (part number 3941176) is identical to the one used in the 1968 model year (large journal).  This is a tuftrided forged-steel crankshaft."

Paul
[/quote]

Does that mean a 3279 crank is the same as a 1178?? Keyway and all? And Just different balancers and timing chain covers???
[/quote]

So if the 68 - 69 Crank have the same Identical  keyway,  the 69 style 7708  Balancer and timing cover will time out correctly, it should work great. 

[69Z28-RS]

Two parts, being 'identical', yet having differing part numbers .. does not jive with the GM's practice, OR that of most any other significant manufacturer... 

Accomplished manufacturers - such as GM during the period in question - change their PN's ONLY when a design/manufacturing change makes it necessary, as each new PN does generate new costs.

(Note:  Inexperienced and poor manufacturers very often change/iterate their part designs - sometimes in very significant ways - but do NOT change their PN.)