Correct 427 4-bolt main crankshaft

[Steve Antonucci]

I'm in a quandry and perhaps member(s) can set me straight. I am building a 69
L/71 ( 427-435hp ) engine back to its former glory. I am currently on the
crankshaft portion of the project. Here's where the fun starts. What is the
correct crankshaft for this 427? I have several 396's that used the 3856223
forged crank. 4-bolt variants were cross-drilled & tufftrided. What were the
corresponding crankshafts for the 427-400hp, 427-425hp, 427-435hp, L-88 & ZL/1?
I have seen too many '6223 cranks on ebay that sellers claim were 396/427
crankshafts. But, acording to Alan Colvin's book, the 396 & 427 crankshafts
were different in that the width of the counter weights were different.
Evidently due to the differences in piston weights of the 396 & 427. What is
the truth? I was actually hunting the coveted '7115 crankshaft for this engine,
but perhaps that is an L/88 - ZL/1 crank only. Currently on ebay there is an
L/88 crate engine ( reported to be ) that has the '6223 crank. What gives?!!!

Did 1969 4-bolt main 427 engines use the '7115 crank and/or the '6223 crank?

HELP !!!!!!!!!!!
Steve

[Clem Z.]

Re: Correct 427 4-bolt main crankshaft

any forged 3.760 stroke GM crank can be used just get the rotating assy balanced by a good auto machine shop. competiton products sell 3.760 stroke GM cranks at very low cost

[Mike M.]

Re: Correct 427 4-bolt main crankshaft

howard cams was running a special last month, new big block cranks for 99 bucks which included shipping. mike

[Clem Z.]

howard cams is part of competition products

or vice versa

[Mike M.]

Re: howard cams is part of competition products

clem: i bought a couple of howard cams cranks. cardboard box they came in make me suspect they weren't made in the use. any thoughts? PS. we're autoxing at the cumberland airport oct 30 and 31 and having a pig roast at our farm sat nite is you're inclind check out nationalroadrally.com. regards, mike

[Clem Z.]

Re: howard cams is part of competition products

they may be forged outside the USA,it would be a good idea to mag them before using them. CP advertised that the ones they had listed on their website were genuine GM. i will be there if my C-6 ever shows up. it is over 3 weeks late now.i talked to john maher and he said he was going.

[Joe L.]

Re: Correct 427 4-bolt main crankshaft

Steve----

As excellent as his books are, I believe that there may be some inconsistencies in Alan Colvin's book on this subject. I am quite confident that the '7115' forging was used for 68-69 L-88/ZL-1 engines only. This crankshaft was known as GM PART #3942411 (1968 and early 1969) and GM #3967811 (later 1969). This crankshaft is a 5140 steel forging.

The '3856223' or '6223' crankshaft forging was used for most 396, 402, and 427 applications. It may or may not be the case that those with the complete '3856223' forging number were originally used for 396/402 applications only and those with the '6223' forging number derivative were used for both 396/402 and 427 applications. In any event, the '3856223' and '6223' were machined into several different finished crankshaft part numbers. Also, the '3856223' and '6223' can be used interchangeably between all internally balanced big blocks assuming that the reciprocating assembly is balanced (which anyone would be foolish to assemble an engine without doing), The '3856223' and '6223' are a 1053 steel forging.

Also, the '7115' forging was actually used for both 396 and 427 applications. However, I believe that the 396 and most of the 427 applications for this crankshaft was heavy duty truck.

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. That's not to say that a '7115' might not have "crept into" a non-L-88/ZL-1 from time-to-time. Functionally, the cranks are interchangeable.

As far as the eBay L-88 short block with the '6223' crankshaft, keep in mind that this engine is a much later SERVICE engine. It may even be an engine that was "field assembled" from new GM parts. In any case, there are many possible reasons that the '6223' crankshaft could have been used in this engine regardless of what its origin is.

[Steve Antonucci]

Re: Correct 427 4-bolt main crankshaft

Thanks Joe !

I think you have cleared this subject up for me nicely.

Yours is easily the most clear and concise response I've ever gotten
on this subject. And belive me, I have beaten this up many times.

Steve

[Joe L.]

Re: Correct 427 4-bolt main crankshaft

Steve-----

Also, keep in mind that the crankshaft for the L-72 and L-71 427s was different than that used for the L-36 and L-68. The crankshaft for the SHP engines was cross drilled and nitrided. However, I still think that it was generally the '6223' forging. Alternately, it MAY have been another forging not mentioned in Colvin's book. That forging, if it ever existed, may have been GM #3882842. That number definitely WAS the part number for the 66-69 SHP crankshaft. It MAY also have been the forging number used for SOME crankshafts.