Riddle me this?

[rvaughnp]

2.5 Deck height 206.1
Internals:
Stroke - 75 stroke (37.5)
Rod - 135
Piston (Compression height) 34.2
206.7
Measurements taken from http://www.bmwccn.no/rogaland/Mahle_m20.html



Edited picture from original.

Got it. (edited)

[fiftytakedowns]

I think the top of the piston (edge) is still flush wiht the edge, thats just the dome FOR SUPARRR compressionz

[rvaughnp]

The black ring in between the white lines is the side of the piston sticking out. Sorry for the not so sharp pics, my camera is not working with my laptop.

--Edited pic up top.--

[Rob]

would be level when there's a head gasket maybe?

[Conrad311]

I think the clearances would be so close even with the head gasket that the it could do some damage. And the compression ratio would be higher and high rpm combustion pressures would probably blow out the head gasket.
did you measure your block specificly? if not is there any chance of the deck being machined before? could account for the numbers being off

[nando]

it's completely normal. it makes for a good quench area in the combustion chamber (note how the 885 head is shaped like the tops of the pistons).

[2002maniac]

don't pull a jordan. :) Make sure you check valve clearances once you've got the head on.

[rvaughnp]

I realize all the previous posts. I guess i didn't make the question clear enough.
My question is in the 206.7.
If the centerline measurement from crank to deck of the block is = 206.7 and the: stroke/rod/piston = 206.7.
Why is there a 1mm (or so) actual difference?
I will be checking clearances prior to starting anything. Just curious if anyone knows where the difference is coming from?

[nando]

well you are trusting measurements off the internet. That's where I think the error probably is.

[SpecM]

^ he's right, all the b25's and s-eta have a domed piston like that

[rvaughnp]

well you are trusting measurements off the internet. That's where I think the error probably is.

You refering to the "actual" length/height of the crank/rod/piston ratio?

But these are "common" known measurements for the above mentioned items.? Well, some thought the 206.2 was common on ETA blocks, I guess its time to physically measure mine.

[nando]

yeah, that's another error. eta blocks have the same deck height.

all I know is it's normal for it to stick above the deck.

[rvaughnp]

I posted http://www.r3vlimited.com/board/show...01#post1689001 info that should put that ETA misunderstanding to bed.

I will try to get the crank out to measure the block and then measure each individual part. It is only a curiosity to me... but may make a difference to others that are trying to figure CR or whatever else.

Thanks for replies.

[rvaughnp]

I will try to get the crank out to measure the block and then measure each individual part.

yeah uh... Thats not going to happen. Trying to measure the block, rod, piston, crank through???... with a Autozone bought micrometer in a garage for a missing mm. Not.

I guess that curiosity of mine will have to subside.:hitler:

[rvaughnp]

Potential answer from Aptyp:

http://www.r3vlimited.com/board/showthread.php?t=151788