Stroking/boring M20B25/B27: Sectioned blocks show critical dimensions. PICS!

[digger]

The deck height on these blocks are as follows

B25 206.2mm
B27 206.0mm

cant comment of whether material has been removed

the depth of the bore on both is the same at 134.5mm

[digger]

B27 oil gallery plug i pressume also big welsh plug on eta


B25 oil gallery plug i pressume


nothing drastically different.

[digger]

B27 Exhaust Side External View


B25 Exhaust Side External View


B27 Intake Side External View


B25 Intake Side External View

[digger]

I'm interested in the oil gallery to bottom of bore dimension. That is where the supposed internal clearance benifits of the eta block are.

is my biggest question to will do.

[tinkerputzer]

I'm interested in the oil gallery to bottom of bore dimension. That is where the supposed internal clearance benifits of the eta block are.

[digger]

i have a junk eta block with the big plug at the back. im gonna cut this bitch up. suggestions and what do people want to look at?

ill measure

-deck height
-cylinder height
-bore wall thickness between and on thrust and no thrust side
-position of oil gallery relative to bore
-position of oil gallery relative to bottom of crankcase

[digger]

you shouldn't have to cut into that part of the block if you use the 89.6mm crank and S52 rods. AFAIK you only need to clearance things with the 84mm crank because the counterweights are larger in diameter.

some aftermarket rods have larger shoulders than the OEM rods especially H-Beam rods with unnecessarily wide beams , among other reasons ;)

[tinkerputzer]

When i test fit my engine (89.6mm crank and s52 rods) using the stock pistons the rod shoulder was just kissing the bottom of the bore. This was while it was still stock 84 mm bore. So i figured once it was bored to 86mm it would be fine. I cleaned up some of the rough casting lines at the bottom of the bore just to be safe though. Clearance at final assembly was some where around .020"-.030"

[nando]

you shouldn't have to cut into that part of the block if you use the 89.6mm crank and S52 rods. AFAIK you only need to clearance things with the 84mm crank because the counterweights are larger in diameter.

[LJ851]

A sawzall? Holy cow, you are a baddass. How many blades did that take?

Believe it or not, one blade for whole thing. I used a milwaukee blade and was pretty impressed.

[bmwstudent]

A sawzall? Holy cow, you are a baddass. How many blades did that take?

[whodwho]

That is one of them

See if this is what you were looking for

http://www.scribd.com/doc/12801628/Mahle-Pistons-M20

http://web.archive.org/web/200505261...Mahle_m20.html

[digger]

I was ok with your take on it, it was all those saying it was 206.7 that I have always tried to correct ;)

i thought the internet rumor was that the ETA blocks were 206.2 from C/L to deck and thus different to the B25?

does anyone have the mahle piston chart? i cant find a clear version. i thought i had it on one of my hard drives but cant find it.

[whodwho]

I was ok with your take on it, it was all those saying it was 206.7 that I have always tried to correct ;)

[digger]

the deck height on mine is 206.2 and stack height 206.7 so the piston sits 0.5mm above deck giving a nominal squish clearance with 1.75mm gasket of 1.75-0.5 = 1.25mm 0.05" which is a number thrown around at being upper end of whats considered good

that is my take on it atleast