<VV> 61 Loadside update and questions
BobHelt at aol.com
BobHelt at aol.com
Mon Nov 24 19:06:17 EST 2008
Hello Lon,
We haven't hear much from you lately. Nice to kinow that you're still around
and kicking. Well, you certainly entitled to your opinions, but much of what
you are referencing just isn't backed up by the facts (as opposed to opinions).
Please see below for more on this subject.
Regards,
Bob Helt
In a message dated 11/24/08 2:05:42 PM Pacific Standard Time,
corvairs at pacifier.com writes:
>
> But we also know that most head gasket problems were actually
> caused by lack of understanding regarding torque patterns and ratings.
>
>
No we don't know this. How did you come to this belief? What facts do you
have to support this? What we do know is that because of problems with the head
gaskets on early production, Chev went from a copper gasket to a folded steel
gasket in order to get a handle on the poor gasketing area on these EMs. We
know that it was a design fault which was, as I said, corrected in 1965 with a
larger gasketing surface.
>
>
>
> >Jugs bored 40
> >over are already marginal in sealing surface and to even consider going
> larger
> >is a major mistake in my opinion.
> >
> >In addition, I would be very concerned about the roundness of these jugs.
> Any
> >jug already overbored and subjected to this kind of heat has got to be
> >distorted.
> I have advised that people, looking for more hp in early motors (also
> 1964) go to a full .060 over. I have never seen nor have I ever
> experienced unusual head gasket or distortion problems with .040 or .060
> over in these motors.
Good for you, but very dangerous. An EM jug bored out 0.060 has a knife edge
biting into the gasket. This causes two concerns, one that the knife edge just
isn't a good enough contact area to hold back the combustion process. (again,
if this was so great, why did customers have gasket failures and why did Chev
go to the larger area in 1965?) Second, 35 lb-ft torque on this knife edge
tends to cut into the gasket and cold flow the aluminum in the head right below
the gasket. This cutting and cold flow cause an increase in clearance whis
relieves the head torque and sets up the cylinder for future head gaskle
failures.
Just take a look that the knife edge that a 60 over EM cylinder presents to
the gasket and you will convince yourself. Why would you want to use such
suspect components anyhow?
> > Why would you want to even consider reusing these jugs?
> >
> Now, that's another matter, as the engine in question had obviously been
> severely overheated. I wouldn't reuse much of any of the engine.
> >If I were you I would toss all of these jugs and set an 0.030 overbore
> limit
> >on any EM engine.
Since you still are not convinced, please perform this simple bench
experiment. Take a newly bored cylinder and place it on the work bench. Then place an
inside micrometer across the bore, opening the micrometer until it just
supports itself across the bore.
Now, without disturbing the micrometer, place your hands outside the cylinder
90 degrees from the direction of the micrometer and squeeze the cylinder
between your hands. You will find out that the little pressure from your hands
will distort the cylinder and allow the micrometer to fall out of the cylinder
where you placed it.
So you see that overbored cylinders can easily distort. Ray Sedman has stated
that cylinders are often at 0.002 in out of round after reboring on his
excellent equipment and that it is necessary to use a torque plate to insure
roundness. Even then with a perfectly round cylinder it is impossible to know what
happens when the engine comes up to temperature.
As for the rest of your comments, it sounds like you are trying to justify
your business and processes. Maybe you turn out error free products, and maybe
not. But even if you do, you are operating in a very risky area overboring EM
cylinders so much in my opinion. Maybe your success has mostly been just luck.
I still would recommend to everyone concerned that they limit their EM
overboring to 0.030 in. And for Jamie, that he NOT reuse these cylinder. Maybe they
will work just great. But if they don't, then it's another rebuild. Why take a
chance? 600 degrees he said!!!!
> >
>
> 2) We see no correlation between year and overbore size and distortion
> rate.
So you are saying that despite thinner cylinder walls from boring, the
cylinders remain just as rugged and distortion free as before! Bull-ony. Do you
expect anyone to believe that?
>
> Lon
> www.corvairunderground.com
>
Bob Helt
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