I have personally installed too many valve seats to remember. At one time
in my life, I was in a partnership with a guy in an automotive engine
machine shop. I spent many hours pulling seats, grinding away material that
was damaged by anti-freeze corrosion, then welding, then re-machining seat
pockets and pressing in new hardened seats. Finally, cutting new guides and
finally a three angle valve seat. Literally hundreds of them. Only had a
few failures, most of them attributed to being in too much of a hurry to
exercise sufficient caution to do it right. My fault, no one else's. So
what does this have to do with Oldsmobile "smogger" heads? Well, quite a
bit, actually. The alloy content of the heads is important, because of the
expansion rate. It is vital to know how much expansion takes place, and at
what temperature it occurs. Valve seats are "interference fit". That is
when the outside diameter is actually larger than the bore it is pressed
into. This is accomplished by heating the head until it expands larger than
the seats. In some cases, the seats must be super cooled, usually with a
CO2 fire extinguisher. -90° Farenheit is damn cold. Bare handed, it will
destroy your skin. So, heat the head, cool the seats, and press them home.
Then after temps have equalized, a ridge is rolled around the seats. They
will not fall out. Ever. Water cooled engines will not approach the
critical temperatures needed to expand enough for the seats to come loose.
Obviously, precision tooling, very sharp, and precision machinery are all
involved. Hand held tools won't work.
Jim Hupy
Salem, Oregon
On Mon, Dec 21, 2020, 1:15 PM Ken Henderson via Gmclist <
> I'd have said the hardened seats started in '72. But Google disagrees:
> =====================================
> When did GM start using hardened valve seats?
> 1971
> 1971 was the first year for induction *hardened valve seats* from the
> factory as far as I know. All engines by then had low compression ratios in
> 1971 compared to 1970
engines.Jan 29, 2011
> =====================================
> I trust that. And know from experience that trying to use Chevrolet
> inserts won't work -- they're too thick and intrude into the Olds water
> jacket.
> Ken H.
>
>
> On Mon, Dec 21, 2020 at 3:45 PM Robert J. Gogan via Gmclist <
>
> > I purchased a used J head from a 1975 Oldsmobile Cutlass 455. The
> > rebuilder that I am using cannot tell if the exhaust seats were induction
> > hardened
> > during the original build. He can install hardened seats if I insist but
> > he is concerned that can open up a can of worms. Any engine overheating
> or
> > exhaust restriction will cause the seat to become undone in the head.
> > This already happened to me in my air cooled Briggs and Stratton riding
> lawn
> > tractor. Mice had built a nest under the air cooling baffles and the
> > engine over heated and the hardened seats popped out. Tried some
> internet
> > magic
> > epoxy to rebed the seats but the fix lasted for only one trip around the
> > lawn.
> > Does anyone know if GM was supplying J-heads with hardened exhaust valve
> > seats in 1975 so I don't have to deal with this problem?
> >
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