Engine internal specs... M20 vs. m10, m42, m50, m52, s50, s52, m54, s54 etc.

[Accota]

Ixer did it, but he never finished that motor (or at least he never posted about it).

if it's an N/A application I bet it would be fine.

Yes only NA, with 264/252 cams

THere's also the M52b25 piston which has ch 32.8 and the material above the top piston ring seems even thicker. But I presume has nothing to do with crown thickness?

Stock M54b30 has about 6mm crown thickness, 4mm between top piston ring and top

[nando]

Ixer did it, but he never finished that motor (or at least he never posted about it).

if it's an N/A application I bet it would be fine.

[Accota]

Since e30tech is dead ...

So has anyone actually shaved M52b28 pistons and recut valve pockets in them?

Based on 7mm crown thickness, would shaving 2.3mm and cutting 2mm valve pockets in them make them too weak?

leaving 4.7mm crown seems acceptable but 2.7mm at valve pockets seems very thin.

Application is M54b30, trying to boost CR to 11,3:1

Thanks

[JiXer]

if you plan on a new engine just find a second hand block and use it. that way you have measurements.

Im sorta shifting this conversation over to the e30tech post...

http://www.e30tech.com/forum/showthread.php?p=1374882#post1374882

[digger]

Damn it! Really?
That's the only number I have seen. I don't have the means to measure that accurately and I don't have a block with a crank in it. I'd really just need to be close enough to not bother with the wrong pistons. The actual mock up would determine everything for final assembly measurement.

if you plan on a new engine just find a second hand block and use it. that way you have measurements.

[JiXer]

Damn it! Really?
That's the only number I have seen. I don't have the means to measure that accurately and I don't have a block with a crank in it. I'd really just need to be close enough to not bother with the wrong pistons. The actual mock up would determine everything for final assembly measurement.

Careful using 206.7 as the block height in your calculations, that is the stack height of the stock B25 and not the M20 block height

75 /2 + 135 + 34.20 = 206.70 and we know the piston does not sit flush

[LJ851]

this

the two b25 blocks i remember measuring were 206.2mm so piston 0.5mm proud. with a 1.75mm gasket thats a 1.25mm clearance between piston and head

This is what i measured as well.

http://www.r3vlimited.com/board/showthread.php?t=285315

[digger]

Careful using 206.7 as the block height in your calculations, that is the stack height of the stock B25 and not the M20 block height

75 /2 + 135 + 34.20 = 206.70 and we know the piston does not sit flush

this

the two b25 blocks i remember measuring were 206.2mm so piston 0.5mm proud. with a 1.75mm gasket thats a 1.25mm clearance between piston and head

[JiXer]

Yeah, Im sure I wasnt the first to think of this, but its a tough thing to search for and I couldnt find anything solid.
I have sooooo many other projects I ned to finish first, but I really wanna mock one of these up some day soon.
And then find a cam and porting guru to really maximize the potential.

you'd have to measure the M54 and S52 piston crown thickness to determine how much you can shave off. IIRC, the M52B28 are ~7mm thick which is plenty. also, it's been done before.

[whodwho]

Careful using 206.7 as the block height in your calculations, that is the stack height of the stock B25 and not the M20 block height

75 /2 + 135 + 34.20 = 206.70 and we know the piston does not sit flush

[nando]

you'd have to measure the M54 and S52 piston crown thickness to determine how much you can shave off. IIRC, the M52B28 are ~7mm thick which is plenty. also, it's been done before.

[JiXer]

Well, I'm editing/deleting my other list bc it was wrought with errors.
2 things changed in the basis for this. I actually need to use the iX block which is an M20B25 block which eliminates the chance of using a shorter deck early-m20b27. That and correcting my earlier error leaves me with a deck height of 206.7mm. Earlier I was confused and was using an M50 deck height.
So... this is what I have come up with.

2.8L
M20B25 Block (206.7mm)
M52B28 Crank (84mm)
M50B25TU Rods (140mm)
M54B30 Pistons (84mm / comp. height - 28.32 shaved 3.2mm down to 24.7)
*Might be a bit much to cut off the pistons?

M20B25 Block (206.7mm)
M52B28 Crank (84mm)
M52B28 Rods (135mm) (I believe these are forged and the 135mm M20 rods are not?)
M52B28 Pistons (84mm / comp. height - 32.8 shaved 3.1mm down to 29.7)
*Might be a bit much to cut off the pistons?

3.0L
M20B25 Block (206.7mm)
M52B25 Crank (84mm)
M52B28 Rods (135mm) (I believe these are forged and the 135mm M20 rods are not?)
S52B32 Pistons (86mm / comp. height - 31mm shaved 1.3mm down to 29.7)

There was mention on e30tech about using some 85mm pistons which would be PERFECT and it seems MB has TONS of options. I would need to do a little more research and part number digging, but to be realistic, I don't have access to MB like I do BMW parts. I basically have all of these internals available to me dirt cheap if not free.

[nando]

if you can cut the pistons, then use the M52B28 pistons, rods, crank, etc - the whole assembly. there's plenty of crown thickness on the M52 pistons to shave a few MM off and cut the valve pockets.

[JiXer]

Crap, I had the wrong deck height to start with. Damn it!
Sorry. This thread afficially sucks. Will try to save it :) Stand by.
Also, keep in mind I have access to a mill and lathe so I can cut piston tops however I want. I also should have a head here that I can cross section for test fits.

[shadowracer]

How bout these links.....?

https://www.zealautowerks.com/index

https://www.bgsoflex.com/displacement.html