On Jan 15, 10:43*am, "
wrote:
History repeats. *Only this time the government is paying the bill for
a Porsche powered English blimp.
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I'm delighted to see that my Memory Bone has not been attacked by this
cancer :-) But I'm still stuck with trying to recall the details that
went into a successful finned pattern, as explained to me (about 40
years ago!!) by a fellow Chief. I really hate to say it but my best
recollection of FINS was that in each case, the FIN had to be made of
two pieces of CLEAR lumber, glued back-to-back. For example, to
produce a 1/8" fin, measured at the tip, you had to start with two
pieces of clear wood about 3/16" (each!) at the root or base of the
fin. These were then sanded or planed so as to provide a MINIMUM
draft of 1/8".

Right now I'm looking at FIFTEEN fins (vs the stock VW head's which
have only eight).

Using the best head I could find (I had no idea how many of the damn
things I've accumulated!) and making up half a coffee-can of green
sand (using a mix of aluminum oxide(?) & #100 silica, there's no way
in the world I can come up with a green-sand having enough strength to
produce a fin even as deep as the STOCK depth (ie, approximately 1").
Plus, I run into an interesting problem: With a draft of 1/8" and a
depth of 1", things appear to work out pretty well. But to then make
the depth ANY GREATER than 1" I will have to increase the distance
between the fins, which is presently 1/4" for the four HOTTEST fins
but only 3/16" apart for the five coolest fins. Then comes the main
problem: I don't have a planer, which sanding down each of the
'biscuits' I'll need to make the fins.

Then comes an even trickier problem: There is a clear parting line
showing how the fins were rammed-up & parted but the flask holding the
fins next to the valve gallery has to make use of a false bottom (I
know what it is but I've forgotten the name of the thing) so that you
end up using three flasks, one of which is rammed and pulled
perpendicular to the other two.

-Bob