3900 crank in a 3.1 block

goatnipples2002 · Post by **goatnipples2002** » Wed Oct 25, 2006 6:48 pm

Since I have niether to check clearances...just from the numbers how would I be able to tell if a 3900 crank would fit in a 3.1 iron head block?

Does anybody know if it will?

If not what about a 3500 crank?

Series8217 · Post by **Series8217** » Wed Oct 25, 2006 6:59 pm

Shaun41178(2) · Post by **Shaun41178(2)** » Wed Oct 25, 2006 8:34 pm

The Dark Side of Will · Wed Oct 25, 2006 9:54 pm

The 3900 has the same stroke as the 3.1, but larger main and rod journals. You'd need to have EXTENSIVE machining done to the block in order to fit it.

Why do you want to do this? Are you just looking for a forged crank?

Series8217 · Post by **Series8217** » Wed Oct 25, 2006 10:01 pm

The Dark Side of Will wrote:The 3900 has the same stroke as the 3.1, but larger main and rod journals. You'd need to have EXTENSIVE machining done to the block in order to fit it.

Why do you want to do this? Are you just looking for a forged crank?

It also has different bore spacing. Do the journals even line up?

The Dark Side of Will · Wed Oct 25, 2006 10:08 pm

Bore spacing? I thought the bore centers were the same but moved outward so as to be not centered over the crank.

Series8217 · Post by **Series8217** » Wed Oct 25, 2006 11:17 pm

No, I think they couldn't fit the 99mm bore on the VVT 3500 and 3900, so the bore spacing was increased by 1.5mm. What would it help to just move the bores over?

I think the crank you can swap is the non-VVT 3500 crank (though it still requires tons of machine work).
There is no non-VVT 3900.

SappySE107 · Post by **SappySE107** » Thu Oct 26, 2006 1:16 am

Series8217 · Post by **Series8217** » Thu Oct 26, 2006 1:19 am

SappySE107 wrote:It can be modified to fit. The bore spacing didn't change. We bolted a 3500 head to the 3900 block. The deck is wider but not longer or anything. You can fit the 3500 lower intake in there still as well so the valley didn't change. Its just further out.

The 3500 non-VVT?

SappySE107 · Post by **SappySE107** » Thu Oct 26, 2006 1:36 am

The Dark Side of Will · Thu Oct 26, 2006 6:47 am

Series8217 wrote:What would it help to just move the bores over?

Move the bores out from the cam tunnel so they can be bigger.

The Dark Side of Will · Thu Oct 26, 2006 6:48 am

SappySE107 wrote:It can be modified to fit. The bore spacing didn't change. We bolted a 3500 head to the 3900 block. The deck is wider but not longer or anything. You can fit the 3500 lower intake in there still as well so the valley didn't change. Its just further out.

There are some threads on 60V6 on the 3900 as well as the 3500 crank.

So as the clarify, you're saying that the older heads will bolt to the new block, and that the older manifold will bolt to the new block and heads (not necessarily that the ports line up, just that the parts bolt on).

goatnipples2002 · Post by **goatnipples2002** » Thu Oct 26, 2006 10:49 am

The Dark Side of Will wrote:Why do you want to do this? Are you just looking for a forged crank?

I was unaware that those cranks were forged I just thought they were steel, but yes a forged crank would be nice. Eagle makes a steel 2.8 crank, but I want a 3.1/3.4 crank.