Correct or confirm... Crank Casting

[El_Diablo]

i believe this is one of the signs of a forged crank



what do you guys think? ive never seen ground down casting lines from the factory and if you look you can pretty much tell it wasnt ground down at all, the other said of the crank has a similar sized casting ridge so im pretty sure this might confirm i have a forged crank without running any numbers

[Joseph Upson]

Hard to tell with that picture.

[El_Diablo]

i'l try and get one with more light in the next hour

[El_Diablo]

i know these pictures suck but i only have a camera phone and im working in the basement...



this is actually lower down on the crank, only slightly but it seems the casting flash takes a curve on either side, its atleast a 1/4" in the smallest areas (prolly larger actually) and is slightly raised, to me this seems like a forged crank but i guess i should've payed more attention to such casting marks back when i was working in a machine shop :/

[bszopi]

The way I was told to determine if its forged or not is to tap it with a hammer. If it "rings", then it is forged. If it just thuds, then its not.

[El_Diablo]

well seeing as it is still in the block im pretty sure it would "thud"

[Joseph Upson]

I'm assuming this is a 3500 crank in which case you can check to see if there are any numbers on the end of the snout that would tell us, also the steel crank looks suspiciously morphed with rounded lobes in some areas, it is also very shiny in some areas, then again my engines have been under 10k so that aspect may vary. I think the four digit number for the steel crank is 7484.

[El_Diablo]

wondered how long it would take someone to notice


i know about the snout end numbers but that has yet to let us know if these cranks are cast or forged, that is exactly what im trying to figure out here

what do you mean when you say morphed and rounded lobes? pictures? the crank is pretty clean and "shiny" for being 30k miles (gotta love seasoned blocks ) but i dont see that meaning anything at all really

[Joseph Upson]

The numbers confirm it as the forged steel crank. I made that distinction while talking with someone from GM parts direct and noting the weight difference between the two crankshaft part numbers they provided at somewhere around 5 or 6 lbs. The steel crank looks more like a raw casting, the cast iron crank has more cut and trimmed surfaces I recall. The pictures you are providing must look really good from your view because they aren't very telling from mine. I know what you are looking at, the casting seam on the front throw of the crank, it should be wide on the steel crank and more hairline on the cast crank.

[El_Diablo]

that is only if it is truly forged which had yet to be proven from what i had heard, it seems that all my research has shown they they are indeed steel but noone seemed to know

if you highlight the pictures you can see a lil bit more, sorry they look like such crap, i took them with my phone in dim conditions



im fairly sure this is a forged piece though

[ForcedFirebird]

I'm assuming this is a 3500 crank in which case you can check to see if there are any numbers on the end of the snout that would tell us, also the steel crank looks suspiciously morphed with rounded lobes in some areas, it is also very shiny in some areas, then again my engines have been under 10k so that aspect may vary. I think the four digit number for the steel crank is 7484.

I was referancing this thread in another, so sorry to bring it back from the dead. I was talking to someone about this crank and they said GM hasn't used cast iron in any blocks for quite some time. They use a steel casting, can anyone confirm this?

[Joseph Upson]

I know of no steel cranks used in any of the 3400 and below general mills v6 engines that ever had mention of a steel crank. There is a one off version of the 3400 with the later crankshaft design they may have it.

It's a hard call as to whether the crankshaft is forged or not, as GM sometimes uses the term in reference to known forged parts and sometimes they don't. The 3800 rods are referred to as powder metal and forged powder metal from what I recall.

The 3.6L crankshaft is addressed as forged, a new twist is the mention that newer rod and main bearings are lead free I suppose suggesting more strength if you consider the fuel cutoff points all being above 6k for all of the later V6 engines as well as having hp peak at 6k or more unlike the 3.4 DOHC which could spin over 6k but apparently has a power peak below that making it a waste to spin it that high.

One things for sure, the steel crank forged or not is stonger than the old cast crank and given that there are two cranks for the non VVT 3500 both of which have been posted picture wise, GM used cast iron for cranks at least as late as 2004 when the 3500 debutted.

[ForcedFirebird]

Factory cast cranks are steel. I don't know when the last time GM made a cast iron crank.

Here's what was said on another board by an avid V8 builder. I am unsure of his extent of knowledge on the 660's, but he knew about the bore spacing in the VVT 3500's and 3900's and brought that up when I mentioned the 3500 crank being offset ground. He did not know about the non-VVT 3500's, though.

Now I'm interested to know if the 600's cranks have been cast steel and now forged, or were they cast iron and now cast steel, or even were cast iron and now forged.

Where could we find this pertinant information?

[bszopi]

I still have a couple questions that I was needing to ask my contacts at GM about, so I could add this to the list. Now if I could only remember the other questions...