In Depth: Crankshafts

[SappySE107]

I have a 2.8 FWD crank and a 3.4 DOHC crank. I need some details explained since I dont know what is a counter weight vs anything else. It is interesting to see the DOHC is knife edged though compared to the 2.8 crank. Here are some pics that I have so far. What I need is a good explanation of the crank's job in the engine (i can probably think of something but I like as much input as possible) as well as explaining the differences between the cranks in our engines. Chris has 3.1 crank pics but I gotta hunt them down.

Anyway, here are the pics I have.

Thumbs posted, go here for full size pics.

http://www.60degreev6.com/indepth/Crank/

DOHC
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DOHC
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DOHC
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[RebelGT]

Odd that this is from a Navy publication, but here is a pretty good explanation of crankshaft terms, theory, oiling, etc...

http://www.tpub.com/engine3/en3-53.htm

Its several pages long, so you need to click NEXT a few times. It looks like there is a bunch more info as well on other aspects of the engine.

[SappySE107]

Ill have to bookmark that and read it. Ill link to it though once the section is up. Time to hunt through Chris's cd of pics for the crank pics.

[Anonymous]

can we use the 3.4 dohc crank in our 2.8 blocks with the rods and pistons

[SappySE107]

As far as I know, it all swaps right in. If a 2.8 crank works in a DOHC, I think it works the other way around

[sd_iconoclast]

My machinist claims that the 3.1 crank is the same crank as the DOHC crank. This seems logical but I have begun to wonder if he just lostg my crank. DOes anyone know if they are they same? Are they made of the same material? Do they have the same part number?

[SappySE107]

Different part number, same casting number. Not sure on metal used, or anything GM did to them after they were cast.

[geoffinbc]

The knife edge is very aparent in thoes pictures. If you look on the DOHC Crank you can see the dual beveled edge on the leading side of the crank counter weight. This probabally helps reduce turbulance and would also relieve stresses in the metal.

The 2.8L Crank does not have this. Now did 3.1L and 3.4L (pushrods) also have this knife edge design?

[SappySE107]

both sides have this knife edge to them trailing and leading. The 3.x and 3x00 have this design as well.

[TheDirtyBen]

i don't remember seeing the knife edge on my 94 3100 crank. btw, does anyone want my 3100 busted crank?

[bszopi]

Give it to Ben so we can get some pictures!

[TheDirtyBen]

i will, if i ever see him

[XLR8ING]

I've had a 3.1 MPFI crank side by side with a 3.4 DOHC crank, and from what I remember, they LOOK identical. Casting numbers were definately the same. I took pics, but I'll have to dig them up again.

The 3.4 crank was for a buddy. He converted his 2.8 Camaro motor to a 3.1 using the 3.4 crank and H562CP pistons.
I'll see if I can find the pics and post them here.

[bszopi]

Well, I just pulled a crank out of an 01 3100 for a guy, so I'll take some pics to put up on the site, as well as get some numbers off of it.

[Wolf]

you should weight the two cranks to see if theres a difference

3.4 pushrod crank is edged(and it says 3.1 on on of the counterweights if I remeber right)


when I take that gen 2 2.8 apart I'll see if its crank is edged or flat