Hey guys, I was just wondering how many here have seen GM NON-Twist forged steel crankshafts from production motors?

I myself have seen/owned a total of 2 3.76" stroke cranks from 366/427 tall deck motors. Both were GM nitrided, 1053 steel (casting number "6223") cranks. As of a few days ago I have seen one non-twist 4.00" stroke crank (454) that I bought from "Epistuff". The casting number is "7416", its a GM nitrided, GM cross-drilled, and is forged from 1053 steel.

Even my crank grinder from the local machine shop has never seen a 454 non-twist crank in 30 years of business. However, he has seen a few 3.76" non-twist cranks, two of which were mine.

I have had a few people telling me for years that GM never produced factory non-twist cranks, but I have disproved that pics and/or the crank(s) themselves. Its like the old saying, "The proof is in the pudding.".


-------------------------------------------------
Incase anyone doesn't know the diff between non-twist and twist cranks...

Non-twist cranks are forged with the rod throws in the correct position, therefore the parting lines are only on the first and forth rod throws.

Twist cranks are forged with the rod throws all inline, then "twisted" after forging to get the rod throws in the correct placement. On twist cranks the parting line is on ALL the rod throws, not just on the first and forth.

Most aftermarket forgings are "non-twist".

The proof is in the pudding, hmmmm. Well lets put it in these terms, GM never offered a non twist raw forging so it's hard to believe they have finished cranks.

I went to the foundry ads saw cranks being forged, a very nasty process, and all the forgings were of the twisted type.

The shop I worked at made cranks from raw forgings and if non twist forgings were available we would have been using them.

After market is a different thing.

The strongest cranks are twisted forged cranks, not billet cranks.

Well I get the crank back from the machine shop on Monday or Tuesday (mains needed turning 0.010"). So then I'll take a few pics and post them of the non-twist crank and a few of another "twist" crank to compare the diffs.

Pictures are pretty hard to ignore, wouldn't you agree?

Also, I just noticed that these guys are selling GM non-twist 3.76" (2 piece seal) cranks and 4.00" (1 piece seal) cranks.

http://www.competitionproducts.com/2004CompProducts.pdf

Page 67.

If they weren't selling the "real deal" then they would be facing lawsuits. I doubt they'd risk it.

The only GM non twist forgings I know about are small blocks cranks. That crank on that page has it's own part number, the GM part no they used had been around since 1965. I tried to use that number at GM parts direct, nothing.

I cn't find a single reference to any non twist rat crank made by GM, unless it's a small block.

What difference does it make anyway? You think it will run faster with a non twist crank???

Gee Wally,how's come people pay such huge sums for billet cranks,when cheap twist type forged cranks are stronger?(brings back memories of "Leave it to Beaver")I do agree though,about GM not producing a non-twist 396/427 crank. Steve

Honestly, if someone could explain to me why these cranks are missing the parting lines on #2 and #3 rod throws, I am all ears. That is EXACTLY how aftermarket non-twist forgings look.

Oh, before someone says they were grinded off, nope, they are untouched.


Originally posted by Wally:
The only GM non twist forgings I know about are small blocks cranks. That crank on that page has it's own part number, the GM part no they used had been around since 1965. I tried to use that number at GM parts direct, nothing.

I cn't find a single reference to any non twist rat crank made by GM, unless it's a small block.

What difference does it make anyway? You think it will run faster with a non twist crank??? Respectfully Wally, if you can still doubt their existance even after I post some pics, I don't know what I can do to prove to you otherwise.

Do I think I'll run faster? No, but that's not the point. All I was trying to ask is who else has a forged steel, GM produced, BBC NON-Twist crankshaft. That's all. I wasn't looking to start a flame war about their existance.

Originally posted by 67chevy2:
I do agree though,about GM not producing a non-twist 396/427 crank. Steve Since I don't own any more of the 366/396/427 non-twist forgings and have since deleted the pics, I can't prove of their existance. Unless you count the ad list on Comp Products.

However, since I do own a 454 non-twist forging, I can at least prove that much.

When I take the pics, I'll make sure to get the casting number and one of the rod throws without the parting line in the same pic. Since ALL GM "twist" forgings have parting lines on ALL the rod throws, it can't be said its an aftermarket crank.

Sound good?

Gentleman, I too have never seen a factory produced non-twist forged crank. Does that mean they do not exist? Certainly not, I've seen stranger things happen. I also have seen the ads by Competition Products claiming GM non-twist forged cranks. Personally I think these cranks were manufactured by the aftermarket for GM, just like Brodix did when they made the Pontiac Pro Stock heads. They cast them with a Pontiac part number making them legal for NHRA Pro Stock. Just my .2 cents

Rob

Originally posted by 66rat:
Gentleman, I too have never seen a factory produced non-twist forged crank. Does that mean they do not exist? Certainly not, I've seen stranger things happen. I also have seen the ads by Competition Products claiming GM non-twist forged cranks. Personally I think these cranks were manufactured by the aftermarket for GM, just like Brodix did when they made the Pontiac Pro Stock heads. They cast them with a Pontiac part number making them legal for NHRA Pro Stock. Just my .2 cents

Rob Thanks Rob.

I would and could totally accept that the non-twist forgings are made by an aftermarket for GM, especially if there was any proof to support that.

I wouldn't of even challenged it if it weren't for the plain-jane GM 427/454 casting numbers found on these cranks. Especially since I have had two matching casting numbered 366/427 cranks next to each other, one non-twist, the other "twist".

Cable, over the years I have seen various GM performance parts whose numbers will NOT show up in any common liturature. Among the weirder parts that I have seen in the last couple of years was an individual runner fuel injection manifold for a pre '68 small block - complete with GM casting numbers!

Maybe you have found something that was made in similar small numbers.

Other than the obscure and unusual factor, is there some other reason why any of us should be excited about this crankshaft? If you had found a 4.25" crank like that then I would have said it was from the Can-Am era, otherwise I don't know what to make of this one.

Thomas

Originally posted by Bomber '67:
Cable, over the years I have seen various GM performance parts whose numbers will NOT show up in any common liturature. Among the weirder parts that I have seen in the last couple of years was an individual runner fuel injection manifold for a pre '68 small block - complete with GM casting numbers!

Maybe you have found something that was made in similar small numbers.

Other than the obscure and unusual factor, is there some other reason why any of us should be excited about this crankshaft? If you had found a 4.25" crank like that then I would have said it was from the Can-Am era, otherwise I don't know what to make of this one.

Thomas =
I'm with Thomas,,

With GM I learned a long time ago to never say "never or always" :D
I don't have a clue whether GM itself did a non twist crank but I do know either Callies or Cola or at least one of the better crank suppliers had cranks with GM forging numbers on them for circle track classes where you had to run a "stock" crank but as far as I know they supposedly got the raw forgings from GM.
To be honest I never paid any attention whether the were twisted or not ;)

Thanks for the replies guys. I haven't posted any pics yet because I have been working 12 hour days with my new job and haven't had time to pick the crank up from the machine shop.

Hopefully I can get down there tomorrow morning before work and take some pics after I get home around 7pm PST.

Until then.....

I have no comment on what GM has or has not done, but I can shed some light on the forging process and provide some exceptions to having a parting line. A crankshaft is forged in a large forging operation called a press. The forging force is supplied by hydraulic assist to a very heavy ram. Forging press machines can have an effective range of 100 tons and up. The quality of a forging is dependent on a couple of things, base metal and quality control. Of the 2, the actual forging process is highly dependent of quality control. The best explanation for a lack of a parting line in a forging was most likely an undersized ingot or an oversized ingot to start with. The parting line is produced when the the dies are hammered together. The excess material will bulge out, yielding a parting line.
Either your crank had an excess beyond what is normally exposed and was trimmed off clean, or there was little excess on those couple of throws. The other explanation is that the dies were near the end of their life cycle and had been remachined enough so that they were completely closed. Just so everyone understands, the goal in forging is to yield as little to no parting line as possible with a forging that meets the QC requirements for dimensional accuracy and structural integrity. The way the operation is done, depending of the quality and age of the dies, there could have been 1000 units produced with the same identifiable traits as what you are seeing on this particular crank.
The issue of twist vs nontwist is not a concern. The forging process assures us that the grain structure will run linear to the forging. By twisting the forging, you will get a curve to the grain pattern, still linear though and without void. As a comparison, casting processes today are advanced enough to control the formation of voids which develop as the metal cools.

And incidentally, all forgings start out from a cast piece of metal. When the steel is melted, it is poured into molds, cooled and sold off as ingots. The ingot will be reheated, cut down, reheated, elongated, twisted, shaped, hammered, reheated again, dropped, bent, beat up and on and on until the metal finally makes it way to the finished part machine area. Doesn't hurt the structural integrity of the metal at all.

Yes, a forge shop hammers/presses metal to make the shape whereas a foundry pours molten metal in moulds that cools to form the shape ..

I've been in more shops of both kinds then I can remember when I worked for the old firebrick plant, APGreen Refractories Co. in Mexico, MO years ago as "Ferrous Foundary and Forging Industry Specialist"!!

You haven't lived until you hot-gun castable repaired a foundry's duplexing channel induction holding furnace's cover/lid holding molten cast-iron at 2,900 degrees F right at the slag notch level!!

I was what 3 feet from the metal line if that far away?? I was up at Grede Foundry, Iron Mountain, MI years ago if I remember right??

pdq67

Here you go guys:

http://www.chevelles.com/showroom/bluerebl/454non.jpg

http://www.chevelles.com/showroom/bluerebl/454non1.jpg

http://www.chevelles.com/showroom/bluerebl/454non2.jpg

http://www.chevelles.com/showroom/bluerebl/454non4.jpg

http://www.chevelles.com/showroom/bluerebl/454non5.jpg