[Healeys] A90 Head Update

Alan Seigrist healey.nut at gmail.com
Tue Feb 2 19:01:39 MST 2021

Hi Bob -

This gasket was put on the car only about 5K miles ago if you can believe
it, but the car sat for about 10 years afterwards...  I've checked both the
head and deck with a rectifier (see pic), both are very nicely flat and do
not need to go to the machinist.  Both are flat to within 1/1000 on the
surface... which is less than the error on the rectifier!

I have the previously removed very old copper gasket which I saved and it
has no signs of gas leaking between cylinders compared to this newer gasket
that I just removed.  I discovered a few things:

   1. The old gasket is made with better quality, softer copper, and is
   thicker than the newer gasket that was put on.  The old gasket that showed
   no problems is 1.8mm thick after being installed, the new gasket that
   failed is 1.5mm thick after being installed.  The old gasket is very
   nicely marked as to orientation, directions, copper compression rings are
   thicker, etc., etc.,  Clearly the older gasket was made to work in
   circumstances where the mating surfaces weren't always perfectly flat.
   2. I highly suspect the mechanics that installed the head last time did
   not torque the head in the proper sequence, quite possibly working from the
   outside in.
   3. The head stud mount holes on the deck were raised a bit in couple
   places and may have caused the head to deflect a little, possibly, but they
   don't seem to have been enough to make a difference... I have already filed
   those holes down.  Micheal Salter has told me to run a countersink to debur
   the hole.

It's a weird one, I think possibly a combination of all three issues
above.  Let's see how she goes after I finish the job.  Ultimately one
thing I learned is I cannot anymore rely on mechanics that I do not know
well to do work on my car... I end up having to redo everything.



> On 2/1/2021 11:23 PM, Alan Seigrist wrote:
> > All -
> >
> > Got the head off.  Sure enough the gasket blew between 3&4 .  some
> > evidence of gas flow between 1&2 as well. Last pic is of me standing
> > in the engine compartment lifting the head off, just to make all of
> > you jealous ... :D
> >
> > Cheers,
> >
> > Alan
> >
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