S50b30 pistons, US vs EURO

[IlovM42]

Hi everyone.

looking to built a little N/A M42, with stock crank and S50b30 pistons (86mm bore 81mm stoke) but the problem is that here in France it's hard to find S50b30 pistons at a good price but I keep looking and i want to enlarge my possibilities

So my question is, does the US S50b30 pistons are the same as EURO S50b30 pistons? I know that there is a lot of difference between the two engine but they seem to have same bore and stroke so i guess pistons are the same?

If you have an idea of this.

Thanks in advance.

Mat

[keflaman]

Hi Mat,

In regards to your question the pistons share the same outside diameter of 86mm, however, it appears there are significant differences:

-Euro S50 -USA S50 -M42  

Piston Specifications:

   -Euro S50
    Length [mm]50,6
    Cylinder Bore [mm]86
    Surface
    Bolt ? [mm]21
    Production Number85 V 105
    Compression Height [mm]31,6
    Bolt length [mm]59
    Recess Depth 1 [mm]3,72
    Valve Pocket Depth 1 [mm]3,09
    Valve Pocket Depth 2 [mm]5,86
    Standard Size [STD]
http://www.autopartoo.com/oem/bmw/11251402390.html#

-USA S50
    Length [mm]51,8
    Cylinder Bore [mm]86
    Surface
    Bolt ? [mm]22
    Production Number86 V 134
    Compression Height [mm]32,8
    Bolt length [mm]56
    Recess Depth 1 [mm]3,5
    Valve Pocket Depth 1 [mm]0,52
    Valve Pocket Depth 2 [mm]3,11
    Standard Size [STD]
http://www.autopartoo.com/oem/bmw/11251404961.html

-USA M42
    Length [mm]51,15
    Cylinder Bore [mm]84
    Bolt ? [mm]22
    Production Number84 V 155
    Compression Height [mm]31,65
    Recess Diameter [mm]70
    Bolt length [mm]54
    Recess Depth 1 [mm]4,5
    Valve Pocket Depth 1 [mm]1,65
    Valve Pocket Depth 2 [mm]1,85
    Standard Size [STD]
http://www.autopartoo.com/oem/bmw/11251721446.html#

I don't think you have any plug-n-play options staring at you.

[IlovM42]

Waouh this is informations! thanks you Keflaman!
So US S50 pistons seems to be an option but need to be carefull with valve and head clearance, but they will give a lot more RV than EURO S50 pistons

Going to see that, but it's easier to take off some mm of a piston than adding them!

but need to see to if finfing US S50 pistons is easier/cheaper than EURO S50 pistons

[keflaman]

If I were you I'd do a lot more searching for information rather than pistons at this point.

Hang around, there's bound to be some folks with a wealth of information and experience to offer you more and better advice than I can give you.

[IlovM42]

don't worry i don't buy/do anything for the moment, only gathering the more information I can