.

By choosing your template material carefully, and then using a ball-pein hammer [very carefully] to repoussé the profile of your specimen into the card.

Then remove the card and cut round the outline.

… Similar to making paper gaskets from scratch.

MichaelG.

Edited By Michael Gilligan on 13/09/2021 21:32:38

^^^
MichaelG.

Perhaps you need a third reference point, like that hole on the left hand side

3 points are better than 2

Edited By Ady1 on 13/09/2021 22:51:15

Hi William,

How about a commercial 3d scan and have them output a file of the flat surface of the head, .this could then be output possibly to a sign-writers stencil cutter. This is food for thought for myself when I need to re-do a head gasket for my1926 Renault, as the previous gaskets re-cut from old gaskets and do not necessarily pass over the head studs.

Regards, Nimble Neil.

Obviously the better ‘engineering’ approach, Pete

MichaelG.

Posted by William Harvey 1 13 / 09 2021 20:43:15

What it doesn't show is how to achieve this and I am really struggling to some up with a
method of doing this.

If I make the template first, how on earth do I ensure the holes for the
valves are correctly located?

If I start by getting a sheet of template material and drilling two
holes with centres corresponding to the valve centres, which I
believe is 1.343"? How do I them transfer the template shape
onto this accurately, ensuring that the valve centre holes are
correctly located on the template.

Stumped…..

——————-

I faced a similar problem in locating matching holes in a blind plate,
although not the same as your situation the solution is much the same.
Seen here in the photo the two halves of a belt housing ,the main
part of the fabrication has some soldered in bosses to hold the cover
plate ,as these were in fairly random locations the cover had to be drilled
to line up with these threaded holes.Set up on the milling machine a
clearance drill is dropped into a hole to set the position and then the
cover plate which is oversize is held in place and just spotted ,the hole
is then drilled ,with the first hole in place the same procedure is followed
until all of the holes are drilled.The oversize plate is scribed around the
profile and bandsawn and filed to match the body of the housing.
The second part is much the same in the the centre hole has to line up
with the location hole in the rear of the body ,the housing is bolted down
and the centre of the location hole is located,the large washer and bolt
fitted to secure ,the cover plate fitted and the opening milled away.

It is useful to have a milling machine to do this sort of thing ,as you have
a pillar drill much the same can be done ,i would think that it would be easier
if you had a sheet metal template and by locating the valve guide with
suitable size rod in the chuck and then using a small drill to spot the
location with the template just held in position ,fixing then the template
with a suitable fixture in the first hole use the same procedure
to locate the second hole.

The way I used to do it was by making a pattern from about 1mm aluminiun and filing it to fit in to the profile so that the top surface is level with the head surface. Drill the two holes through the valve guides. Drop the valves through the pattern and into the guides. Mark the head surface using the outside of the profile and machine/grind the chamber until the pattern is flush with the head surface. Using this method all the chambers can be very accurately ground to the final size. I found over the years that I didn't have to do any more fettling to achieve accurate matching.

I haven't flowed a head for more than 20 years but I have never got all the cast iron dust out of my hands!

You clearly need to make the holes first then. It should be a simple task to find the valve guide separation.

Create identically spaced holes on your template material then form the outside profile. If you use thin perspex sheet you can see through to pick up the original profile.

regards Martin

.

I agree, Martin … ‘though I did assume that William already knew [or was soon to confirm] the separation, when he wrote:

… centres corresponding to the valve centres, which I believe is 1.343"

MichaelG.

You could have drilled a couple holes in your template well oversize and close enough to the valve centres, then make a couple of "penny" washers which fitted the valve stems exactly. Place your template carefully in the valve chamber, apply epoxy adhesive to the penny washers and position the washers over the oversized holes and drop your valves (With oily stems) through the penny washers and let it all harden off.

Bob