3.0L, 84mm bore, 89.6mm crank?

[SpecM]

what c/r comes from an m54 rotating assembly and an 885 head?

[supernaughtIX]

I picked up an M54 bottom end today. Looks like I'm going to follow you on this.

I do have access to CNCs and a lathe so I'm going to try to work with the M54 pistons.

Chris, I haven't made it all the way through that 34 page e30tech link, but does it discuss machining M54 pistons somewhere?

[Wh33lhop]

Hm. Plenty of places are stuck with 91 octane, 9:1 is still a little on the low side. What are you doing to the top end?

[Raxe]

Our gas sucks, weak 91 octane is about as good as it gets here. My set goal is something very usable and simple, I don't want be hunting for higher octane if I don't have to.

I also haven't ruled out a turbo someday down the road when there's nothing left to do. ;P

[nando]

Why 9:1? Going turbo?

[Raxe]

I'll be going all the way with it, but I ended up going with new 85mm 9:1 JE pistons through IE. Unfortunately I just don't have the skill or equipment to machine these pistons to what I need, and there's no sense in paying someone else to do it for me when I can just outright buy what I really want.

If someone already worked with a lathe/CNC machine it would be a pretty sweet project though.

[RobertK]

The 89.6mm crank drops right in and spins freely, no modification needed.

M20 135mm rods hit; they can probably be shaved down if needed but M54 135mm rods clear without issue as they're leaner and lighter right from the start.

Didn't think about the M54 rod being lighter / thinner and from what I've been told its a pretty strong rod. If you pull it off I would love to see some pictures of the build.

[Raxe]

The 89.6mm crank drops right in and spins freely, no modification needed.

M20 135mm rods hit; they can probably be shaved down if needed but M54 135mm rods clear without issue as they're leaner and lighter right from the start.

[nando]

Dunno. I haven't ever heard of people needing to clearance the block for the 89.6mm crank. Maybe it's because IE uses M20 rods.

[RobertK]

eta combustion chambers are "bathtub" shaped, not hemispherical. And many aftermarket pistons aren't very good..

I'm pretty sure the 89.6mm crank clears no problem. you may have to shave the intermediate shaft, but there aren't normally block issues. the M52 crank counterweights being larger is why there are more clearance issues in general (even if you don't use the 130mm rod/i piston combo).

also pretty sure the OP said it already fits and clears no problem.

Just because the crank by itself clears the block doesn't mean it will once the rods are installed. See the note from IE's website for installation of the 89.6mm crank. Its the rod angle that creates the clearance issue.

Note: This kit requires modification of the block at the bottom of the bore for connecting rod clearance. We can supply kits with any combination of bore diameter and compression ratio by special order - call us.

[nando]

eta combustion chambers are "bathtub" shaped, not hemispherical. And many aftermarket pistons aren't very good..

I'm pretty sure the 89.6mm crank clears no problem. you may have to shave the intermediate shaft, but there aren't normally block issues. the M52 crank counterweights being larger is why there are more clearance issues in general (even if you don't use the 130mm rod/i piston combo).

also pretty sure the OP said it already fits and clears no problem.

[RobertK]

M5x use a pentroof combustion chamber, and a centered spark plug. M20 885 is hemispherical with an offset spark plug. the shape of the M20 piston is related to that.

there's tons of material to machine off the M54 pistons. just go read the link I posted.

I think you only need to clearance the block for the 84mm M20B28 crank, which is actually larger in diameter than the S52/M54 crank?

Completely forget about the spark plug orientation but still, the eta pistons and aftermarket pistons that come with the IE kits are not domed so what's up with that?

http://www.iemotorsport.com/bmw/E30-engine/m20-32.html

According to IE the 89.6mm stroke of the S52/M54 crank is what has to be accomodated. I think you are thinking of the counter weights on the M52 crank that must be shaved to clear stock "i" piston skirts.

[nando]

Provided that machining 1mm off the top of the pistons didn't take off so much material it compromises the integrity of the piston the process itself would actually be very simple on a lathe.

The valve recesses shouldn't be too much of a challenge either.



If that's the case then why aren't eta pistons or any other M5x/S5x piston domed but yet the cylinder head is?

The dome is there to create a target compression ratio not even out the combustion. You can create a similar effect by aggressively decking the cylinder head.

EDIT: Also, you might have to machine out some material from the lower side wall of your block for the bottoms of those rods to clear similar to how the IE 3.1l stroker kit does.

M5x use a pentroof combustion chamber, and a centered spark plug. M20 885 is hemispherical with an offset spark plug. the shape of the M20 piston is related to that.

there's tons of material to machine off the M54 pistons. just go read the link I posted.

I think you only need to clearance the block for the 84mm M20B28 crank, which is actually larger in diameter than the S52/M54 crank?

[RobertK]

Provided that machining 1mm off the top of the pistons didn't take off so much material it compromises the integrity of the piston the process itself would actually be very simple on a lathe.

The valve recesses shouldn't be too much of a challenge either.

Yes! I honestly don't get why people think that it is acceptable to not match the two. Even and complete combustion is not only better for the longevity of the motor, but it is essentially more efficient.

If that's the case then why aren't eta pistons or any other M5x/S5x piston domed but yet the cylinder head is?

The dome is there to create a target compression ratio not even out the combustion. You can create a similar effect by aggressively decking the cylinder head.

EDIT: Also, you might have to machine out some material from the lower side wall of your block for the bottoms of those rods to clear similar to how the IE 3.1l stroker kit does.

[pantelones]

you need the piston dome to suit the 885 chamber. IMO get some pistons from JE they will replicate the correct dome

Yes! I honestly don't get why people think that it is acceptable to not match the two. Even and complete combustion is not only better for the longevity of the motor, but it is essentially more efficient.