M50 bore tolerances?

[GunMetalGrey]

I need to re-hone my block, and wanted to know what my bore should be(how far from stock it can be, e34 m50b25tu,) it Will have new rings of course.

[trackjunkie21]

I need to re-hone my block, and wanted to know what my bore should be(how far from stock it can be, e34 m50b25tu,) it Will have new rings of course.

Stock is 84mm. s50 is 86mm. People say not to go more than 86 on Those blocks.

[GunMetalGrey]

Sweet, thanks!

[jrdeamicis]

You can go up .025, but you need to match the pistons to the bore size. You can easily order .025 pistons w/ rings.

S52 is 86.4 if I remember correctly.

You should just swap out to the M52 crank and do a 2.8 setup with .025 pistons. Best of both worlds.

[GunMetalGrey]

Feel free to post up links of the parts your suggesting!

[e46s54dr]

If you plan on running stock pistons with your block then the tolerance should be right around .0015 (+/-.0003") based on the stock bore size. Any more may result it piston slap.

[GunMetalGrey]

Anyone know what the stock bore is on them?

[e46s54dr]

84mm

[GunMetalGrey]

So the fact that my bore is like 83.99 is odd?

[e46s54dr]

Thats sounds about right... 84 is just the approximate number. You need to measure the top, bottom, and middle of your cylinder to ensure that theyre straight. Then measure your pistons. Subtract the 2 and youll get your clearance.

[Wanganstyle]

Feel free to post up links of the parts your suggesting!

you could order:

overbore pistons for a M54b30
Rods and crank from m54b30 or s52b32 US.

bore the M50b25 block to match the overbore new pistons.
install rods and crank+pistons.

then you have 3000cc

[GunMetalGrey]

Would that result in a higher compression ratio? Or does the crank have a smaller stroke.

[ForcedFirebird]

If you plan on running stock pistons with your block then the tolerance should be right around .0015 (+/-.0003") based on the stock bore size. Any more may result it piston slap.

Stock pistons are 83.98" (b25) and the bore is 84mm. Just a hair tighter than 1.5 thou...

.02mm=.0008"

[NbAmTwE]

Would that result in a higher compression ratio? Or does the crank have a smaller stroke.

You can do either with that setup. They're custom pistons he's referring to.
This is similar to the Frankenstein M50 setup just with overbore and custom pistons. So you can choose pistons that will raise/lower compression depending on na/FI

[Wanganstyle]

Would that result in a higher compression ratio? Or does the crank have a smaller stroke.

it would have compression like a M54b30 or s52b32; m54b30 is a small bore s52. Not very high compression, a S52b32 usa is a low performance engine with relatively low compression.

The 3.0 L crank has a longer stroke, that is why the same 84mm bore (or overbore) can equate a total of 3000cc instead of 2500cc.

If you desired 3200cc you could bore your m50 block to 86.4mm and use the s52 crank and rods in your block.