Date: Mon, 3 Mar 2003 23:09:04 -0600
Reply-To: Stan Wilder <wilden1@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: [T2] A cc'ing the heads question-answered
Content-Type: text/plain; charset=us-ascii
I've done some heavy clipping since we got this thing so long.
I didn't say I was getting accurate or more accurate ............. I was
just saying that I liked to know the actual piston to head clearance.
The reason being that cranks can be ground in error, rods can be re
bushed in error, rods stretch, all piston sets aren't exactly to spec
from center of wrist pin to top of piston and bearings wear. In addition
to that heads pull down tighter when they get hot even if the steel
stressed head studs are good.
I've had three sets of cylinders on my bench at one time, #1 used OEM VW
#2 new Cofap #3 new Mahle, I found that there was .030 difference between
the OEM and Mahle between the sealing base and the sealing to head area,
the Cofap fell somewhere in the mid range, the OEM VW were the shortest
(probably for the head gasket purpose) and I see that with base seals and
head gaskets these cylinders would set right to spec.
Running these cylinders without base seals on AMC heads might lead to
trouble.
These variations drive me to disregard much of what I read in manuals and
find a method suitable to me.
A difference of compression of 7.1 vs 7.3 would not even make a
performance difference that you could worry about.
I see that the desirable end result is getting the proper distance
between the piston and head, however you get to that.
I've shuffled lots of cylinders, rod /piston assemblies just to get to a
point that the crush tube measurement is consistent for all cylinders.
Many rebuilders set VW air-cooled for low compression for cooler running
and longer life.
I was shooting purely for a smooth running engine with balanced
compression and as much compression as possible without machine work.
I haven't run a compression test on my 15K engine because It runs very
good and the performance is right up there to ................. well to
what? is the question.
I can say it is a vast improvement over the new engine performance of
first engine I built and removed after 155K. Both engines had all of the
same new parts.
On the first engine (1996 build) I rotated the engine to TDC, I was using
a steel stiffener from a wiper blade that I put down the cylinder through
the spark plug hole. As the piston came up to TDC it would squeeze the
thin flat blade. Number 1 touched the blade and held it tight between the
piston and head, none of the others would seize the blade, it was free to
mover around and even get slight rotation.
That engine was built by Bentley and Hayes specs of setting deck height
by the method you are using.
I can't say that .003 difference would make much difference but I like
having all the same.
If you can remember that car ad where the fellow stood the coin on it's
edge on running engine ......... that is what I'm shooting for.
Stan Wilder
> 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
> ---------------------------------------------------------------
>
>
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