So do I have a Steel crank or not

[Guest]

Some time ago earlier this year during a discussion about the 3500, I missed some additional information on the GM drivetrain site that lead me to believe I had a steel crank in my 3500. Turns out that the steel cranks were designated for the Buick SUV.
While trial fitting the 7x reluctor ring for my about to be turbocharged 3500, I couldn't help but notice how silvery the crank looks, and how heavy it is. A trip to the scale with both the 3500 crank and a 3400 crank yielded the following;

3500 crank: 50 lbs, 3400 crank: 37 lbs.

The only numbers liking to a part number were on the tip of the crank snout;
5010300 and 7484. I didn't get a hit on the parts site but discovered that GM only showed one crank for the type 3500 I have #12577484 until 2006 where I found a listing for #12568259 a fairly cheaper crank. I called GM parts and although they couldn't tell me which crank was steel, they did tell me that the 7484 crank that I have weighs 49 lbs 1 less than I measured and the cheaper crank available in 2006 weighs 45 lbs.

These cranks are found across both the 3500 and 3900 in passenger and SUV vehicles as proposed sometime ago could be a possibility despite what they actually advertised which would be a marketing strategy if you thought your vehicle was the only one that came with it.

So either the more expensive and heavier 7484 is the steel crank or the cheaper lighter crank is the steel crank that's just making up for it's lighter weight and lower mass with it's increased strength assuming it is drilled in various places for lightening it to the tune of 45 lbs.

What do you think?

The twins

[IsaacHayes]

All I can say is I envy you.

[RacerX11]

Foged cranks will have a wider parting line, whereas cast cranks will have a straight, narrow parting line.

http://www.carcraft.com/techarticles/116_0308_crankshafts_how_to/index1.html

[Joseph Upson]

Foged cranks will have a wider parting line, whereas cast cranks will have a straight, narrow parting line.
http://www.carcraft.com/techarticles...to/index1.html

It's about a half inch wide, compared to the 3400 crank which has a thin 1/16" line going down the same area.

[bszopi]

Hmm.. interesting. Here is a pretty clear picture of the 3500 crank that I have.



All of the indications from that Car Craft article are leaning towards a forged crank, from the rough look of the counterweights to the wide parting line. Might just have to take a hammer to it tonight to see if it "rings like a bell".

[patgizz]

yup, forged cranks ding like a bell. cast cranks kinda thud.

[Joseph Upson]

Looks like l was correct in my suspicion some time ago, I ran the part number again and the only vehicles I see listed with the 7484 part number are the Pontiac G6 which my engine is from and the Terraza which it was initially stated by someone was the only vehicle that received it. I'll pull the balancer from my Malibu 3500 later and see what number is on the end of that crank. So the individuals that rained on my parade a couple of months ago need to eat some crow.

http://gm-auto-parts.com/parts.htm

The Uplander and Montana show the lighter crank listing.

[Joseph Upson]

I'm certain it's steel after looking at the article and looking at this post on the 3500

http://60degreev6.com/showthread.php?t=30724&highlight=official+3500+thread

My crank doesn't look like the 3500 crank in that thread, it has rounded counter weights and the wide patch of metal towards the front end of the crank. Great since after glancing through the article cranks have a cycle life expectancy

[bszopi]

Yeah, mine doesn't either... And I am the one who originally told you they were only available in the Terraza. But I was going off of GM Powertrain release information. So anyway, I grabbed a couple more pictures of my crank. They didn't come out the best, but here they are:







And it does indeed ring like a bell. So I guess I have a forged crank. But oddly, mine is from an 04 Malibu. And mine doesn't have any of the numbers that yours does.

[Joseph Upson]

You forget, I mentioned above that it is likely most if not all of the cranks for the 3500 prior to 2006 are steel when it was mentioned in GM documentation for the Terraza and apparently the same year that the cheaper crank apparently started showing up on the parts site according to my searches on it. It was GM documentation that lead me to believe that I had a steel crank under the powertrain data, so maybe it was just a sells pitch to mention it for the Terraza.

I haven't pulled the balancer bolt off of my Malibu engine yet 04, but I suspect it maybe the same, the last four of the part number are behind the retaining nut on the end of the crank, and my crank looks just like yours.

[Joseph Upson]

TURBO TEST DRIVE, never mind the GM piston slap if you can here it, it's been there since day one. I don't have the proper type of video camera to feed to my laptop so the mono sound microphone and its lousy feed into the computer was the best I could do. The high pitched wind like sound might have been the turbo sucking air in more so than wind near the microphone it wasn't in the air stream. Toward the end win the microphone was moved there were a few revs to make the blow off valve audible. You can hear the turbo and blow off valve better from inside and standing outside of the car than the microphone was able to pick up. 2000 3100V6 soon to be replaced with the 3500V6 from the Pontiac G6.

I just tested it and I had to shrink the file so much to post within the site parameters that the quality is below what is necessary for the blow off valve and probably the turbo to be audible.