What Crankshaft Do I Have?

[Robert G.]

On the GM box, the part number is 3967811. My 1983 Corvette Parts and Illustration catalog says: 68-69 (427) W/HD which means L-88 I thought. A later GM Performance Parts catalog I have says 68-69 427 W/H.D. -ALUM...I.D.(#7115), which sounds like ZL-1 with a casting number that ends with 7115. My casting number is 3856223.
I just bought Colvin's book and he says the 3856223 casting was used for 1965-1969 396. Could someone straighten me out on the numbers? thanks

[William C.]

Re: What Crankshaft Do I Have?

The same FORGING was used for many of the 396-427 series engines, different part numbers will reflect different treatments on the crank bearing surfaces or different balancing specs for the factory balance setup. I don't find the finished part number in earlier catalogs, but don't get in the trap of thinking the crank forging number and the part number mean the same thing, they do not. One forging can have several finished part numbers for different applications.

[Joe L.]

Re: What Crankshaft Do I Have?

On the GM box, the part number is 3967811. My 1983 Corvette Parts and Illustration catalog says: 68-69 (427) W/HD which means L-88 I thought. A later GM Performance Parts catalog I have says 68-69 427 W/H.D. -ALUM...I.D.(#7115), which sounds like ZL-1 with a casting number that ends with 7115. My casting number is 3856223.
I just bought Colvin's book and he says the 3856223 casting was used for 1965-1969 396. Could someone straighten me out on the numbers? thanks

Robert-----


In general, the GM #3967811 crankshaft did use the 7115 forging. However, I never have understood why GM could not make a 3967811 FINISHED crankshaft from a 3856223, 6223 or other forging. In your case, apparently they did. The 3856223 and 6223 forgings were not used exclusively for 396 cid engines. They were also used for 427 engines. They are all 1053 steel forgings.

As Bill describes, the forging is then manufactured into different FINISHED crankshafts depending upon machining, journal surface treatment, cross-drilling, etc.

Notwithstanding the above, are you sure the crankshaft in the box you have is the one that was originally packed in the box? In other words, was the box sealed on both ends with STAPLES when you got it. If not, who knows?

By the way, is the crankshaft cross-drilled and do the journals have the sort of "dull" appearing finish of a "Tuff-Trided" crank?

[Robert G.]

Re: What Crankshaft Do I Have?

Joe,
I can't recall whether the box was stapled on both ends when I bought it many years ago-I ordered it from my Chevrolet dealer shortly after they discontinued the L-88 short block. However, the crankshaft has cross-drilled journals, but I wouldn't exactly say they are dull looking.

What had me wondering was a post in the archives where you said:
'I believe that with respect to 1969 Corvettes, the '3856223' or '6223' forgings were used for all 427 application except for L-88/ZL-1.'

Are the L-88 and ZL-1 crankshafts all the same dimensions?

[William C.]

Re: What Crankshaft Do I Have?

Yes, dimensionally they are exactly the same, and complete interchangable as are non-shp carnks and 396 cranks. Differences are in surface treatment and balance.

[Robert G.]

Re: What Crankshaft Do I Have?

Thanks guys.

[Joe L.]

Re: What Crankshaft Do I Have?

Joe,
I can't recall whether the box was stapled on both ends when I bought it many years ago-I ordered it from my Chevrolet dealer shortly after they discontinued the L-88 short block. However, the crankshaft has cross-drilled journals, but I wouldn't exactly say they are dull looking.

What had me wondering was a post in the archives where you said:
'I believe that with respect to 1969 Corvettes, the '3856223' or '6223' forgings were used for all 427 application except for L-88/ZL-1.'

Are the L-88 and ZL-1 crankshafts all the same dimensions?

Robert-----

If you got it from a Chevrolet dealer it's highly likely that what's in the box is what the parts label says. It's not 100% certain since someone could have purchased it, switched cranks, and returned it. However, I don't think there's a high probability of it. I assumed you had purchased it from some private source and, then, there would be a greater chance of a "switcheroo" if the box was not sealed.

In any event, I believe that the L-88 and ZL-1 crankshafts were the same. However, it does depend upon what year model L-88 one is talking about. There were 3 different cranks used over the 1967-69 period. The 3967811 was the last of them and used for either late 1969 or, possibly, only for SERVICE engines after 1969. I'm not sure about this.

What you found in the archives is still what I believe. The 3856223 and 6223 forgings were used for all 1969 big blocks except L-88 and ZL-1. I would refine that by saying that earlier 1969 L-88 probably used the 3856223. Later L-88 (after the introduction of the ZL-1) may have used the 7115 forging.

However, as I mentioned in my previous post in this thread. I don't now and never could understand why an L-88/ZL-1 crankshaft of the 3967811 part number could not have been manufactured from a 3856223 or 6223 forging. In fact, assuming that the crankshaft in your box is the one that originally came in the box which I now consider extremely likely, your situation proves that they could be!

There is one slight caveat to the above that I've never got to the bottom of. First of all, the 3856223 and 6223 forgings are 1053 steel. I don't think there's any question about that. However, for the 7115 forging I have conflicting information over the years, even from GM sources. Some information says that the 7115 forging was 5140 steel. Some information says it was 1053 steel. I don't know of any way to differentiate these materials on visual inspection.

What it boils down to is this: IF the specs on the 3967811 crankshaft call for it to be manufactured of 5140 steel and IF no 3856223 forging was manufactured from 5140 steel , then I don't see how a 3967811 crankshaft could have been manufactured from a 3856223 forging.

On the other hand, IF a 7115 and 3856223 forging are both 1053 steel, then I don't see any reason why a 3967811 crankshaft could not be manufactured from either forging.

clem would be the guy that should be able to add the most to this discussion. I was hoping he would weigh in by now, but, perhaps, he's away. In fact, now that I think about it, he may be having surgery this week.