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Open Bosses in Block and Head


2002#3

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If any of you have easy access to a block and/or head (E12 if it matters) will you be so kind as to count the number of open bosses in each?  I find the following and want to make sure I have not missed one:

  • block:  3 on intake side; 1 on exhaust side
  • head:  6 on intake side; 4 on exhaust side

Thank you.

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3 hours ago, visionaut said:

Help me understand what ‘open boss’ means?

 

Just guessing, but possibly where a stud/fitting goes through the block into the water jacket or a stud on the head goes all the way through and requires lock-tight to prevent oil from leaking out?

 

Mark92131

 

 

Edited by Mark92131
grammer
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1970 BMW 1600 (Nevada)

 

 

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Yes.  Thanks, Mark.  

Maybe open boss is not the correct name.  Probably tapped hole which goes through the wall of the block or head.   Example:  the 4 open tapped holes above the blue exhaust ports in the photo above; 3 have studs and 1 does not.

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If you are talking about the threaded stud holes in the head at the intake and exhaust ports on a E12 head.  The 4 holes above the intake ports and the 4 holes above the exhaust ports are THROUGH holes and go into the cam valley in the head.  When you install studs (especially on the exhaust side) you should use loctite or a sealer because oil will slowly work it's way onto the exhaust manifold/header.  The 4 holes below the intake ports and the 4 holes below the exhaust ports are blind and you don't have to worry about them.   All 16 should have studs in them.  

Edited by Preyupy
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1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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29 minutes ago, Preyupy said:

If you are talking about the threaded stud holes in the head at the intake and exhaust ports on a E12 head.  The 4 holes above the intake ports and the 4 holes above the exhaust ports are THROUGH holes and go into the cam valley in the head.  When you install studs (especially on the exhaust side) you should use loctite or a sealer because oil will slowly work it's way onto the exhaust manifold/header.  The 4 holes below the intake ports and the 4 holes below the exhaust ports are blind and you don't have to worry about them.   All 16 should have studs in them.  

I think you missed a few...

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2 at the oil filter mount, 2 at the fuel pump rod hole (the rod hole does not count), 1 at the water inlet/outlet to the L of the fuel pump rod hole, and 2 more (one on each side of the block).  More?

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The one on the right side of the block below cylinder 4 is the block coolant drain, a short 10mm plug if IIRC. 

On the opposite side just under the intake for Cyl 4 is the passage for coolant to the water choke. 

"Sometimes it's a little better to travel than to arrive”  Robert M. Pirsig

Gunther March 19, 1974. Hoffman Motors march 22 1974 NYC

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Then you have forgotten the threaded plug at the back of the block at the end of the oil galley. The 4 at the back of the head for the distributor housing ( the one immediately below the oil pressure warning light switch takes a special sealing washer under the bolt head. And the large threaded plug at the front of the block in the water jacket.  

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1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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Interesting but I can't appreciate the purpose other than calculating how much thread sealant to buy.

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  • Haha 1

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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For all the "visual learners" (like me), pictures are worth 2002 words.

Here are a few pics of what the pros above are talking about.

 

The top exhaust manifold stud holes are tapped all the way through the head. They are right next to the low-side oil drain holes, which is why thread sealant is needed. They are always bathed in oil and create a stinky, smokey mess if they leak oil onto the hot exhaust manifold. All the other through studs (bosses??) for the upper intake manifold and fuel pump studs are high enough (above the oil return passages) to not cause more than a weep or a seep of oil if not sealed. However, best practice is to use sealant on all the threaded stud holes.

 

OilReturnHole.thumb.jpg.635bac2f86de69cb513cb3f5200efe13.jpg

 

TopIntakeThruStuds.thumb.jpg.5bfc2d258e7fc12c33a60e133d297c08.jpg

 

FuelPumpThruStuds.thumb.jpg.be5b5bd79b121c7aed11da77eed11fc8.jpg

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