3.0L, 84mm bore, 89.6mm crank?

[digger]

Here is some useful info on the deck heights and more

http://www.e30zone.net/e30zonewiki/index.php/M20

http://www.daham.org/16vt/technical/bmwm20/

useful?

i have seen that data years almost 10 ago and everyone refers to the same original piece of info regardless of whether it is correct or not.......
i just checked again and my M20B25 block code 256k1 was 206.2 so i find it unlikely that exactly 0.5mm has been machined off both my blocks. So the answer is to measure as engines are build to fractions of mm and relying too much on internet data is risky. if you were to rely on a measurement you would use the smaller one as you can always skim off the block but you cant put it back 'properly'

also have plotted both a M20B20, M20B23 and M20B25 cams and dont agree with the Wiki data

[gath]

i measured 2 M20B25 blocks that were 206.2mm, coincidence? i think not

Here is some useful info on the deck heights and more

http://www.e30zone.net/e30zonewiki/index.php/M20

http://www.daham.org/16vt/technical/bmwm20/

[gath]

No progress on my stroker for many months now, I've been working on a major project for work, and spent 3 months in india. Now I've got 600 beehive boxes to make before I can touch the stroker again(workshop space conflict).

All I know for sure is the cutting required is minimal, but valve reliefs will be a must. I have to get my M54 assembly back into a block again to measure then cut on the mill.

Wow! That's gonna be a lot of "Bzz Bzz Bzz" n honey Lol, good luck with both projects.

[supernaughtIX]

^^^ How is the progress on the build and did you get the #s to machine down the m54b30 pistons?

No progress on my stroker for many months now, I've been working on a major project for work, and spent 3 months in india. Now I've got 600 beehive boxes to make before I can touch the stroker again(workshop space conflict).

All I know for sure is the cutting required is minimal, but valve reliefs will be a must. I have to get my M54 assembly back into a block again to measure then cut on the mill.

[dustyperez]

here is a page with some stock piston compression height numbers. I am doing this build as well and i searched and searched for a suitable stock piston. I didn't wanna machine one down since i will be boosting. And its also possible to get an almost double thickness head gasket. but in the end i chose cp pistons from vac, yes expensive but they know their stuff.

http://cars.forumsee.com/a/m/s/p12-15951-0209962--calcing-m5x-compression-ratio.html

[gath]

This is m54b30 internals in m20b25 block
44.8mm(m54b30) + 135mm(m54b30) + 28.32mm(m54b30) CH = 208.12 – 206.7 M20B25 BH = 1.42mm

[digger]

i measured 2 M20B25 blocks that were 206.2mm, coincidence? i think not

[whodwho]

Those heights are the stack height of a eta and I engine

40.5 + 130 + 35.7 = 206.2 for an eta stack
37.5 + 135 + 34.2 = 206.7 for an i stack


So with the .7 protusion and a 1.75 gasket would leave about 40ish thou squish which sounds about right

[gath]

I believe the stock protrusion on an b25i is .7mm

you should be able to compare the stack height and see what you get for a protrusion of yours

1/2 stroke + rod length + piston compression height - block height
37.5 + 135 + 34.2 = 206.7 - 206 = .7

This is what seems to be the protrusion in my case
44.8mm + 135mm + 28.32mm CH = 208.12 – 206.7 M20B25 BH = 1.42mm

I 'ope the figures are correct because I have two conflicting sources that give the m20b25 block height as 206.2mm and 206.7mm, feel free to give input.

BTW, Stock headgasket is 1.75mm when compressed.

[CarsSuck]

http://www.r3vlimited.com/board/showthread.php?t=243359&highlight=b25+piston

Theres a good picture of a stock b25 piston in the block in there. The top of the crown is more than 1 mm.

[whodwho]

I believe the stock protrusion on an b25i is .7mm

you should be able to compare the stack height and see what you get for a protrusion of yours

1/2 stroke + rod length + piston compression height - block height
37.5 + 135 + 34.2 = 206.7 - 206 = .7

[gath]

Build one of these over the summer. No machining is required.

Robert, what combo did you use? Like I had said, I wanted to use m20 block, m54b30 crank, rods and pistons, m20 885 casting head (worked on). Any word of advice?

[gath]

I actually don't know the thickness of a stock HG, any knowledge on that? I think they could be between 0.4 - 1.0 mm, but I still don't remember the protrusion being that pronounced to about 1 mm on my last m20 build though. But either way if I'll be working with the m54 pistons, machining has to be done for valve relief and maybe a little skimming. So with the gasket you don't think there would be any contact?

[CarsSuck]

that's shown with no gasket though. even stock pistons protrude a little at TDC.

Doesn't the b25 piston crown stick up, like, a lot? And eta pistons are flat topped?

Seems like the m54 pistons could work well with an eta or 731 head, but then you're stuck with the smaller ports and valves. I wonder how that would balance out in terms of power.

[nando]

that's shown with no gasket though. even stock pistons protrude a little at TDC.