Potential for a S50B30 crank to build a 2.85?

[nickphine]

Just looking at a S50B30 crank on ebay and thinking, I wonder how easy it would be to build a 2.85 using the same principles as a 2.8 (I've just built a 2.8 and if I can do it etc etc)

Crank spec I've got of wikipedia is a stroke of 85.8 mm, as opposed to 84 for the 2.8. From what I can gather, this still fits in with the 1.5 stroke to con rod ratio (128.7mm against 130mm 320 rod).

Deck height could be taken care of by using the block that starts with a 206.5 deck height to start with (think I've read a post by Ant mentioning that block). My logic being I had to skim my block down to a deck height of 205.5, the stroke is 85.8mm which will make it stand 0.9 mm higher than the 84mm crank, so machine 0.1 from a 206.5 crank and you have the correct deck height.

Little bit more off the piston skirts and you have a 2.85 as opposed to a 2.79. Only a tiny advantage I guess but the M3 cranks look only a little bit more than a 2.8 crank.

Am I way off or is this doable?

[eta]

Does not fit the M20 I have been advised reliably.

[nickphine]

Any reasons why? I'm wondering if you can get the 3.2 crank to fit, maybe the 3.0 crank is a possibility. I know there is a right and wrong 2.8 crank, but they both fitted in my block, well with a bit of dremmelness, it was only piston skirt clearance that was an issue.

[e21Jason]

Both the s50b30 and s50b32 crank will fit the block but you cannot bolt the m20 crank damper or timing drive gear to the s50 crank

The m3 crank that fits is the US spec one

Jason

[CHR1S1990]

as above, US M3 crank with a 89.6mm stroke also found in:

* 2000-2005 E46 330i/330xi
* 2000-2006 E46 330Ci
* 2000-2003 E39 530i
* 2000-2002 E36 Z3 3.0i
* 2003-2005 E60 530i
* 2003-2005 E85 Z4 3.0i
* 2004-2006 E83 X3 3.0i
* 2001-2006 E53 X5 3.0i
* 2003-2006 E60 530i

look up reggid's car on here, he's used this crank in an m20. Ive got one cleaned up on the shelf for a later project

[HairyScreech]

other problem is the rod bearing journals are unique to the s50 cranks iirc.

[nickphine]

All good info, thanks for that, looking at the prices of those engines they all appear to be too much money at the moment.