David,
What you just described from Isky is called case hardening: most commonly a heat
treating process, although there are other ways to surface harden (i.e.:
ion-nitriding, silicone nitriding can be applied to friction surfaces only) the
nearly finished camshaft is heated to a predetermined temperature in an oven,
then
cooled; this causes a recrystallization of the metal. A smaller grain structure
results in a harder metal, and smaller grain structure results from faster
quenching. This whole process isn't very different than what you'll see
watching a
blacksmith heating, hammering (work hardening), and finally tempering, by
dropping
the hot horse shoe in a bucket of water. Case hardening AKA surface hardening is
nice because it is a hard, wear resistant, but brittle surface on a softer, but
flexible substrate. If the camshaft were uniformly hardened, it would be more
prone
to chipping or breaking. A camshaft can only be ground a certain amount before
the
case depth is exceeded. Nothing wrong with Isky cams... they do know what they
are
doing.
Now back to the question at hand; the question always comes to mind " did I do,
or
fail to do something to cause this?" IMHO, many factors can come into play here,
but I can only surmise the reason for Ernest's severe wear only on cam lobes 1
and
8 has to do with a defect in the original heat treating process, not something
he
did wrong. It is commonly known that connecting rod bearing 3 will almost
always be
the first to go. I defer to historians or ones like Lawrie and Ed, who have vast
experience with engine internals, to tell us if there is a similar lesser known
pattern of wear in camshafts. I am unawear of one (no pun intended, but I
simply
could not resist ;^} ).
Jim
David Councill wrote:
> I've seen it - but it was with an Isky reground cam. Less than 20000 miles
> of use and quite a few lobes were worn away. Isky claimed MG cams are
> "soft" underneath the hardened surface or something to that effect and thus
> did not make good rebuilds (of course they didn't tell me that before they
> reground it). I put in a cam from another engine and now have more than
> 100,000 miles on it with no evident problems.
>
> David
>
> At 10:53 PM 2/27/2001 -0500, James H. Nazarian, Ph.D. wrote:
> >FWIW, I have seen the innards of some 20 MG engines, but have never seen or
> >heard of the ailment you describe.
> >
> >Jim
> >
> >Ernest Shirley wrote:
> >
> > > I'm in the process of rebuilding the engine of my 78B and I noticed
> > > something that I thought was odd when I pulled out my camshaft. The first
> > > and last lobe on the shaft showed signs of extreme wear...I mean they were
> > > practically round, yet the other six lobes have hardly worn a bit. I
>would
> > > have thought that all the lobes would have worn out roughly at the same
> > > time. Is this typical or should I be looking for something while I
> > have all
> > > these engine guts strewn about on the table. The lifters for the 1st and
> > > 8th valves had some minor pitting but I wouldn't think they caused this...
> > > Any ideas?
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