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DISCUSSION => Engine + Driveline => Topic started by: 1991 E30 M42 on March 09, 2007, 06:35:58 PM

Title: Head Gasket
Post by: 1991 E30 M42 on March 09, 2007, 06:35:58 PM

I'm putting M44 50 over pistons into my m42 and was wondering if I need an m44 overbore head gasket or will an oem head gasket have a big enough bore.

Title: Head Gasket
Post by: cecotto on March 10, 2007, 04:44:52 AM

Quote from: 1991 E30 M42;20925

I'm putting M44 50 over pistons into my m42 and was wondering if I need an m44 overbore head gasket or will an oem head gasket have a big enough bore.

I dont know how much a "50" overbore is, sounds like an imperial measure..

But i can tell you that the BMW OE gaskets are only available in one size, however they come in two thicknesses, standard and +0.3mm.

The bore of the OE M44 gasket is 86mm

(http://m42club.com/forums/attachment.php?attachmentid=729&stc=1&d=1169746925)

Title: Head Gasket
Post by: magnum2066 on March 10, 2007, 05:51:22 AM

Does the thickness of the gasket make a difference of any significance?

Title: Head Gasket
Post by: asubimmer on March 10, 2007, 09:22:31 AM

Quote from: cecotto;20946

I dont know how much a "50" overbore is, sounds like an imperial measure..
 
But i can tell you that the BMW OE gaskets are only available in one size, however they come in two thicknesses, standard and +0.3mm.
 
The bore of the OE M44 gasket is 86mm
 
(http://m42club.com/forums/attachment.php?attachmentid=729&stc=1&d=1169746925)

are you sure .3??  the stock thickness is .069

Title: Head Gasket
Post by: Jimmy Lewis on March 10, 2007, 04:06:06 PM

.069mm is about the thickness of a piece of computer paper, are you sure you don't mean .069cm in which case +.3mm would not not be super significant. I'm probably just talking out of my ass.:D

Title: Head Gasket
Post by: cecotto on March 10, 2007, 04:45:30 PM

Quote from: asubimmer;20953

are you sure .3??  the stock thickness is .069

Partnumbers:
11-12-1-433-950  Headgasket 1.74mm (1.74mm / 25.4mm = 0.0685")
11-12-1-433-951  Headgasket 2.04mm (+0.3mm) (2.04mm / 25.4mm = 0.08")

I have trouble relating to the imperial system, and actually have trouble figuring out why you mix them up.. When you're working on a metric engine why convert everything to inches??  It seems this makes things confusing..

But then again a can imagine you have trouble relating to millimeters the same way as i cant see how much 0.0685" is in my head..

:D

Title: Head Gasket
Post by: 2002maniac on March 10, 2007, 04:51:54 PM

for reference:

1mm=.039"

Title: Head Gasket
Post by: 2002maniac on March 10, 2007, 04:53:08 PM

Quote from: asubimmer;20953

are you sure .3??  the stock thickness is .069

.069 what?  Numbers mean nothing without having units assigned to them. ;)

Title: Head Gasket
Post by: cecotto on March 10, 2007, 05:19:00 PM

Quote from: 2002maniac;20966

for reference:

1mm=.039"

I'm not trying to be a dick, but that is wrong information.. Well not exact-information the conversion is only accurate if you use the factor:

1" = 25.4mm

1mm = 0.03937007874015748031496062992126"

Try looking at page 7 in this document:
http://ts.nist.gov/WeightsAndMeasures/Publications/upload/h4402_appenc.pdf
(Note that only underlined numbers are exact in the documet page 7 table)

From your own National Institute of Standards and Technology

I agree with you on the importance of noting the unit explicitly, without that the numbers have no meaning.

Title: Head Gasket
Post by: 2002maniac on March 10, 2007, 06:13:25 PM

Quote from: cecotto;20968

1" = 25.4mm

1mm = 0.03937007874015748031496062992126"

For automotive purposes, can't we just say that 1mm=.039"?  

I think this is a useful approximation for mental math.

Title: Head Gasket
Post by: 1991 E30 M42 on March 10, 2007, 06:21:04 PM

I'm talking about bore diameter not thickness of the head gasket. 50 thousandths of an inch is equivalent to 1.28mm. the diameter of my pistons is 85,485mm. Will the factory bore size head gasket be big enough.

Title: Head Gasket
Post by: Jimmy Lewis on March 10, 2007, 09:42:58 PM

Thank you all for explaining that so well, without making me feel like a total doucehbag, haha. And sorry for completely missing the first post, I'll stop.:p

Title: Head Gasket
Post by: cecotto on March 11, 2007, 11:39:59 AM

Quote from: 2002maniac;20970

For automotive purposes, can't we just say that 1mm=.039"?  

I think this is a useful approximation for mental math.

The chassis measurement from the center of the rear mounting hole on the front subframe to the center of the rear subframe bushings mounting hole is 2017mm +/- 1.5mm.

2017mm / 25.4mm = 79.409”

2017mm * 0.039mm = 78.663”

The 0.039 factor has a error of 18.9484mm / 25.4 = 0.746"

I think that is a significant error, but then again if you're not measuring long distances the error is not that significant.  But as long as theres no cost assosiated in using the correct conversion factor i think one might as well do it right ;)

Title: Head Gasket
Post by: 2002maniac on March 11, 2007, 11:53:28 AM

I obviously would not be converting such a large number with my method.  However, if I need to know approximately how many thousandths of an inch 3mm is, I'm not going to go find my calculator, I can just do it in my head and be close enough.

Hell, I even round up a thou.  

.04x3 = .120
3mm~.120"

Of course, If I am going to resize a cylinder bore with accuracy,  Or check the distance between my front and rear subframes, I would not do this.  Please be logical and reasonable.

Title: Head Gasket
Post by: 2002maniac on March 11, 2007, 11:56:15 AM

what do you use as Pi?

I use 3.14.

  3.141592653589793238462643383279502884197169399375105820974944592
would be more accurate, but it just isnt useful in most cases.

Title: Head Gasket
Post by: cecotto on March 11, 2007, 12:13:51 PM

Quote from: 2002maniac;21000

what do you use as Pi?

I use 3.14.

  3.141592653589793238462643383279502884197169399375105820974944592
would be more accurate, but it just isnt useful in most cases.

:D :D

I know what you mean, but if you were measuring your chassis out which factor would you use?

I'm not good at math so i always use a calculator, which by the way has a Pi button with all the resulution i need.  :p