Cylinder block crack

[leomarcus]

Hello i have an m50b20 block on my 2800 engine (84x84) turbo application 8.5 :1

I picked up the head after a cylinder number 5 is full of water

I have original gasket for head, now this cylinder seems to have a rought row on cylunder stroke.

I think now it is a crack.

Has other experienced on crack on cylinder on m50b2x block?

thanks

[5mall5nail5]

I have seen a cracked M50 but it was due to hydrolock. Perhaps your cylinder full of water hydrolocked the block and cracked it.

[leomarcus]

Yes head gasket was blown and cylinder was full of water...so it is possible?

[5mall5nail5]

It is possible.

[leomarcus]

Here photo picked from car ...not enought quality my samsung galaxy next do just what it can

[AnK]

m50b20(80mm) and m50b25(84mm) blocks are different. m50b20 bored to 84mm has weak cylinder walls.

[leomarcus]

Seems a very light crack, do you think honing is enought or iron is so bastard that crack will extend to infinite? anyway i think to change block with another one.
But other one i have is another m50b20, very coomon here in italy, m50b25 very hard to find, so "new" block it will be m50b20 bored

What mean different? you mean different iron fusion material? because geometry are the same except for bore so wall thick is same

http://forums.bimmerforums.com/forum....php?t=1764697

[AnK]

No. Wall thick is different!
You can't bore b20 to 86mm(you get hole to water jacket), b25 can be bored up to 87 as I know.
b20 have additional water jacket channels.
PS talking about euro versions...

[leomarcus]

Check link i sent yu, i am a bit confused because i am reading differnt opinion

[bmmrr]

Yes they should be same blocks. euro m3 blocks are different.

[leomarcus]

Ok thanks, so i can safe bore it again.
So i realized crack was for hydrolock from head gasket, and then crack.

So crack was an effect and not a cause

[AnK]

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[leomarcus]

I have cutted old m50b20 block and compared near to b25 block ,they are at end different, wall thickness is different, so boring m50b20 to 84mm bring cylinder n° 5 thichness of 1.5 mm that is not acceptable.
My forged pistons are 83.90

Does anyone know if m50b25 block cilinder is 84.00 on stock? or for example 84.10 or something different from .00?

thanks

[bmmrr]

Can you show it with pictures

[leomarcus]

Here photo of m50b20 bored to 84.00mm.

This is wall between cylinder N°5 and N°6

Any idea of stock m50b25 cylinder diameter ? 84.00/ 84.08 or so?

[Laimis]

Any idea of stock m50b25 cylinder diameter ? 84.00/ 84.08 or so?

Should be 84.0000

[bmmrr]

isteresting . Stock m50b25 is 84mm. Can you show m50b25
Picture with cutted.

[leomarcus]

Not cutted m50b25 , but from water passage yu can see that cilinder are "fat" than m50 b20.

Also taking look at this photo i can realize that is very hard that bmw engineer on original m50b25 last only 1.5 mm of wall like this photo.

I also tried tu put a copper wire in m50b20 hole and it passed from one side of cylinder to another.

Instead on m50b25 not passed in anyway, so i realized m50b25 has smaler water passage between 2 cylinder, so more fat cylinder wall.

Now i am planning to buy an used m50b25 block, my forged are 83.90

Just saw on real oem site, origina mahle pistons are 83.98, does anyone know what is stock clareance between pistons and cylinder on m50?

[coffeeandcigars]

Here photo of m50b20 bored to 84.00mm.

This is wall between cylinder N°5 and N°6

Any idea of stock m50b25 cylinder diameter ? 84.00/ 84.08 or so?

Could you please post that photo again, i am very interested to see it!
I have the same problem as you, cant get a decent priced B25 Block...but i have a B20 that could be bored out a little bit

[someguy2800]

The picture still works for me. The sleeve looks like it’s only 2mm thick or so given the 7mm of spacing between cylinders. No way on earth would I run that with forced induction

[coffeeandcigars]

The picture still works for me. The sleeve looks like it’s only 2mm thick or so given the 7mm of spacing between cylinders. No way on earth would I run that with forced induction

nope for me ...could you please post the link to the picture? It must be hosted somwhere?!

[someguy2800]

Note that an m50b25 block is joined (siamese) between bores. You should have at minimum 3mm of cylinder wall at least even for a turbo motor, and with an 84mm bore there is 7mm of space between cylinders, so I'll let you come to your own conclusion how much cylinder wall is left in the above picture.