Date: Mon, 3 Mar 2003 20:02:54 -0800
Reply-To: Tom Young <tomyoung1@ATTBI.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Young <tomyoung1@ATTBI.COM>
Subject: Re: [T2] A cc'ing the heads question-answered
Content-Type: text/plain; charset="iso-8859-1"
----- Original Message -----
From: "Stan Wilder" <wilden1@JUNO.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, March 03, 2003 6:50 PM
Subject: Re: [T2] A cc'ing the heads question-answered
> Here is the thing Tom.
> AMC heads have a ridge cast into them that seat on the Cylinder / Barrel
> and raise the head surface up from the piston. (additional accuracy,
> information, what ever, do you think you're getting from your technique
> vs. the one I'm using?)
> This clearance is accomplished with a head gasket on OEM VW heads.
I still don't see any additional accuracy. In fact, if you're doing what I
think you're doing, you're losing accuracy if you're using an AMC head.
Yes, there's a ridge built into the AMC heads. Since I'm cc'ing the heads
using a plate that sits on the ridge I'm including in my measurement of
combustion chamber volume the very thin "slice" of head defined by the plane
of the ridge where it touches the cylinder and the plane of the (rather
wide) flat "step" that this ridge creates in the head. (As an aside, it was
in this rather thin area that bubbles would "stick" when I was using water
and prompted my original question under this thread.) I then check deck
height from the top of the cylinder to the top of the piston, add in the
dish in the piston, and I have an accurate reading of the total "crushed"
volume.
If I was using a VW head without the ridge built in my plate would sit right
on the large flat area of the head and my resultant combustion chamber
volume would be smaller than that of the AMC head. But, if I was using the
head/cylinder shim (yes, I know VW abandoned this shim - this is only for
purposes of discussion) then I'd mic the shims and calculate the volume the
shim creates to be added back to the equation.
Now, if you're using a VW head without the built-in shim, then the method
you describe of crushing a brass tube ("spring back" aside) should give an
accurate deck height measurement.
However, if you're using an AMC head then the method you describe will give
you the "real" deck height (top of piston to top of cylinder) *plus* the
"height" of the built-in ridge. Unless you construct a special Plexiglas
plate that fits *inside* the built-in AMC head ridge to measure combustion
chamber volume I don't know how you'd ever accurately calculate CR.
---------------------------------------------------------------
Tom Young '81 Vanagon
Lafayette, CA 94549 '82 Westfalia
---------------------------------------------------------------
