M20B27 Engine Specs

[peerless]

Hello,

I need some help with some engine specs that are required by Venolia to machine my new pistons. So here is exactly what I need:

85' M20B27 Engine

Piston Deck Clearance
Cyl Head CC
Head Gasket Thickness

Please NO guessing or vague information. This has to be EXACT SPECS. I have $600 riding on these pistons and don't want the job screwed up.

Information I already have:
Bore: 84 mm / 3.311 in
Stroke: 81 mm / 3.189 in
Compression ratio: 9.0:1 (82-87), 8.5:1 (super ETA 87-88)
Rod length: 130 mm / 5.118 in
Rod big end bore: 45 mm / 1.772 in
Crank rod journal: 21.8 mm / .858 in
Piston comp height: 35.7 mm / 1.406 in (82-87), 36.2 mm / 1.425 in (super ETA 87-88)

https://www.e30tech.com/forum/showthread.php?t=1729

Thank You very kindly for your help, I am missing my Bentley Manual so I don't really have a way of checking this stuff.

[iXer]

This may be helpful
-> https://www.bmwccn.no/rogaland/Mahle_m20.html

[Madhatter]

piston to deck clearence is 0.01mm for all M20's.

Which head are you using? ill have to sit down and workout the real head volume for you again, the figures people use are incorrect, they arent the chamber volume of just the head, its off by a few cc's (from memory the real figures are something like 34cc for the small chamber head and 37cc for the larger 325i item).

Do they want compressed thickness?

[peerless]

Originally Posted by iXer

This may be helpful
-> https://www.bmwccn.no/rogaland/Mahle_m20.html

Awesome, I was actually looking for that, Thank You.

Head Gasket Thickness and Cylinder Head CC are all I need now.

=D>

[peerless]

Originally Posted by Madhatter

piston to deck clearence is 0.01mm for all M20's.

Which head are you using? ill have to sit down and workout the real head volume for you again, the figures people use are incorrect, they arent the chamber volume of just the head, its off by a few cc's (from memory the real figures are something like 34cc for the small chamber head and 37cc for the larger 325i item).

Do they want compressed thickness?

I am using the '200' casting. Original 'e' semi-closed chamber.
I am assuming that compressed thickness on the head gasket would be what would be correct.

Thank you very much, I really appreciate the help.

[-o<

[peerless]

Well when in doubt, call Jim at Metric Mechanic.

The 200 head casting is at 37cc and the head gasket is 9.5cc's or .0068" uncompressed. Piston to deck clearance is .01mm or about .004", But since it was not mentioned whether it was positive or negative I defaulted at 0 deck clearance.

[Madhatter]

its negative.

[Irish1]

I second calling Jim Rowe at Metric Mechanic. His number's on his Metric Mechanic web-site. He's the Guru of BMW engines, rear ends, and transmissions and is happy to answer any question. His wife is great also: super friendly: she clearly LIKES her husband. Rowe talked to me for 2 hours one time about ways to enhance the breathing on my M20 even though I made it clear I wasn't ready to buy anything. A generous, no-BS, honest guy. I wish I had the bucks to have him build a stroker M20 for my 88 325iS: drive it to his shop, come back a week later, and roar off into the sunset with 80 more HP and Lbs/Ft of torque.

Originally Posted by peerless

Well when in doubt, call Jim at Metric Mechanic.

The 200 head casting is at 37cc and the head gasket is 9.5cc's or .0068" uncompressed. Piston to deck clearance is .01mm or about .004", But since it was not mentioned whether it was positive or negative I defaulted at 0 deck clearance.

[peerless]

I have talked to Jim twice. It is the same story. He loves to talk shop, I think we talked for about an hour just about pistons

Great guy. When he is gone their will be a big void in BMW knowledge missing as well. If I had the money I would also buy an engine from him. I was already looking at his transmissions as well.

=D>

[Tucker]

I know this is an older thread, but wanted to add some data since I found this thread useful.

I just measured the displacement of my eta head at 38.5cc.

I recently replaced all the intake and exhaust valves which may or may not impact the final numbers. The volume was measured twice on two different combustion chambers with identical results each time.