[200q20v] Destroyed my own alternator :(

Dave Haupt quattrodave at yahoo.com
Wed Feb 6 15:54:32 EST 2002

About a year ago I replaced the brushes/regulator on
the alternator in my 1989 200TQ sedan.  Based on info
in the Bentley, this early production car (November,
1988) should have been equipped with a 90A alternator.
 Lots of guys reported to me that the fix wouldn't
last, that something else would surely go wrong soon,
etc, and I just decided to see how long it would last.

Well, it went.  I was preparing to deal with a leaky
PS pump, and had taken the car to the car wash to wash
off all of the Pentosin that had leaked all over the
front of the engine.  After said high-pressure
exercise, when I started the car, the alternator light
was lit.  I assumed that I had nuked the blue exciter
wire, and had to wait for decent enough weather to get

into it.

When I finally got to working on it, said blue wire
appeared intact, and electrical measurements showed
the wire properly connected to where it ought to go.
I even turned on the ignition, loaded the wire, and
measured the requisite 100mA (actually more like 150mA
is what I measured).  Hmmmm.....I tried getting
something out of the alternator, but even feeding it
exciter current and giving it a spin, I got nothing
out of it.

Being unable to pay the Blauvergnugen price for an
alternator, but also not having the tools required to
do the rebuild (it seemed that the bearings were
getting noisy, too), I inquired of a local Porsche nut
what he would do.  He immediately told me which local
alternator rebuild place in town he felt did well with
Bosch alternators.  I called them and a few others.
Price quotes for rebuild (new internal parts including

bearings, stator and rotor windings, diodes, brushes,
regulator, and machining of the shaft and slip rings)
ran from $65 to $110, all with a two year warranty.
The recommended place was the most expensive, and I
went with them because of the recommendation.  When I
brought them the alternator, they exclaimed that it
was not a 90A, but a 110A.  The nameplate was no
readable, but they had 90, 110 and 115 in stock
already rebuilt, and the 110 and 115 were the only
ones with the same two-foot mounting.  Also, their
Bosch manual showed the 1989 200TQ sedan available
with either the 90A or 110A, somehow depending on
options.  The 90A was a single-foot mount, the 110 and
115 are double-foot mount, and this one's clearly a
double-foot.  The Bentley mentions single-foot versus
double-foot alternators, but does not make it clear
that the 90A were all single-foot mounts.  So - I
learned I don't have a 90A alternator.  The previous
owner may have upgraded, or the car may have come this
way, I will never know.  Obviously, an upgrade would
have been a lot of work, what with the different
mounting scheme.  This also explains why Carlsen in
Palo Alto had such a hard time figuring out what
hardware to sell me to re-mount it when I worked on it
a year ago.

His test of the alternator showed that the stator
windings were shorted.  I watched the disassembly.
Aha!  It was VERY clear what had happened.

Remember that PS fluid leak?  PS fluid had gotten into
the alternator.  You know that warning that Pentosin
can has to not let it land on painted surfaces?  Yep,
it acts as a solvent for paint.  Alternator windings
are made with "magnet" wire, which has a varnish-like
substance used for insulation.  Large portions of the
windings had the insulation stripped from them.  It
had flaked off, not burned off.  There was no sign of
any heating on them, but rather what you would expect
if you used a chemical paint stripper, followed by a
water spray.  I had used Pentosin as the chemical
stripper, and then used the car wash for the second
step of the water spray.

So it's not clear how long it would have lasted had I
not destroyed it chemically.  And it's also evident
that I need to curb the car until I can get the
Pentosin leak fixed.  I'm fairly certain that the
Pentosin leak is the PS pump...that was the point
behind the massive engine wash, so I could clean it
all up enough to see where the leak started again.

So, $110 later, and the alternator is hanging under
the car, and I'm waiting for the next good weekend so
I can put the new adjuster bolt (the old one finally
failed after some 3-4 alternator remove/replace
cycles) in and cinch everything back down.

Then it's back to getting the power window mechanism
replaced, and then the PS pump.  Gotta cut back on the
Little Friskies for a while to pay for all of this!

Santa Rosa, CA
1989 200TQ sedan, 144k, hopefully to be back on the
road by April

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