Who pays?

Are you guys reading what viperdoc wrote? The mechanic replaced a belt
with a new one and it came off. I thinks it's perfectly reasonable to
look at the obvious. The belt simply may not have been installed
correctly.
Dave
M35

nrp wrote:
Viperdoc - What type aircraft? Is your alternator driven from the
prop end, or the back end of the engine? If it is driven from the
back end, you have serious internal damper problems in your engine.

It is belt driven off the accessory case. One possible explanation was a
sticking crankshaft counterweight. However, the engine has not shown any
indications of vibrations, such as smoking rivets, cracked baffling, etc.

However, until the new belt was installed, there had never been any problems
with the electrical systems.

I suspect, but will never be able to prove, was that the belt was either not
tightened enough when changed, or the field wire was knocked loose or
kinked, causing the alternator to run intermittently. On inspection after
the fact today, it was corroded.

My standing there watching would not have made any difference- there would
have been no way to tell if the wire was broken, and short of taking the
wrench and tightening the alternator myself there was no way I could tell if
it was loose.

I ran the plane for nearly an hour after the work today, with none of the
same indications, including under a heavy electrical load with lights, etc
in relatively high IMC.

Hopefully, it'll be back to where it was prior to the inspection.

Your problem just might be high frequency torsional vibration on the
back end of the crankshaft. I've seen this shred alternator/generator
drive belts on a C182 in just a few hours. Your alternator will still
work OK with this vibration (it will be about 250 Hz @ maybe 1 degree
p-p or so) but I'd be concerned that the cantilevered gear driving the
crankcase output shaft could break off from fatigue inside the engine
case and create instant and very severe trauma.

You won't feel this vibration because it is torsional, but the
resulting stresses in the propeller and crankshaft are very high.
Someone with a critical ear MAY be able to hear it.

How far is the engine from O'haul? Were the damper bushings and pins
replaced at the last overhaul?

I can't imagine the damper counterweights "sticking". The next
failure could be a propeller blade from dynamic stress. If this new
belt gives trouble, get someone intimately familiar with that engine
involved.

Good luck!

If I followed your posts correctly, the last corrective action was repairing
a corroded wire and that seems to have solved the problem, is that correct?

Disclaimer: I am not an A&P.

I am a part of every repair decision made to my plane. I respect and trust
my mechanic. He does good work and is well respected by a lot of people. But
I know that I am but one, thankfully infrequent customer and he has other
distractions. If the explanation doesn't make sense to me, the repair
doesn't get done until it does. It's a classroom for me and I want to learn.
If I go along with a goose chase, I consider it as much my fault as my
mechanic's. Sometimes, a goose chase is the only approach. Sometimes it's
the easiest. Rarely is it the cheapest. As long as I go into it eyes wide
open, I'll accept the consequences.

The sequence of your events don't seem right. It throws a belt. The theory
is that crankshaft vibrations are causing it. That seems like the least
likely cause but, OK. Replace the belt. It gets thrown again. Why does the
diagnosis now change to be regulators and alternators. That seems to
indicate wild guessing - and, in fact - fickle, wild guessing.

Unless you threw him the keys and said something like, "I don't care what it
costs, just fix the problem," you deserve a break. My mech usually splits
the labor cost of goose chases until we catch the goose. If he declares the
problem but then has to re-fix and re-fix, he bites the bullet.

If this is your regular mechanic and you don't want to cause a scene, just
remind him of it over the next couple of repairs and see if you can coax
some good will out of him.

-------------------------------
Travis
Lake N3094P
PWK

"Viperdoc" wrote in message
...
It is belt driven off the accessory case. One possible explanation was a
sticking crankshaft counterweight. However, the engine has not shown any
indications of vibrations, such as smoking rivets, cracked baffling, etc.

However, until the new belt was installed, there had never been any
problems with the electrical systems.

I suspect, but will never be able to prove, was that the belt was either
not tightened enough when changed, or the field wire was knocked loose or
kinked, causing the alternator to run intermittently. On inspection after
the fact today, it was corroded.

My standing there watching would not have made any difference- there would
have been no way to tell if the wire was broken, and short of taking the
wrench and tightening the alternator myself there was no way I could tell
if it was loose.

I ran the plane for nearly an hour after the work today, with none of the
same indications, including under a heavy electrical load with lights, etc
in relatively high IMC.

Hopefully, it'll be back to where it was prior to the inspection.

This was my original point. There was a certain lack of logic to the whole
process.

The electrical system worked fine until the belt was changed at annual. The
new belt was thrown within two hours.

It was reinstalled by my home field mechanic, but again the belt was
whipping, and I was told this was a symptom of excess vibration due to stuck
crankshaft counterweights. (estimated cost fore repairs- at least $3,000)

I asked the question- why should this occur all of a sudden, when previously
it had been running fine? But, I also realize that stuff happens.

We replaced the belt again, but this time there was no alternator output at
all. Further checking showed no voltage to alternator field- diagnosis fried
voltage regulators (both) as well as possibly bad alternator.

All three components removed and sent for repairs. Result: both voltage
regulators good, alternator needed new brushes, but was also working fine.

Final diagnosis- corroded alternator field wire lug. Replaced the lug, and
after 0.5 h seems to be working fine. Will fly again tonight to test.

My guess- wire was corroded, but making contact until belt was changed at
annual. Movement of alternator caused intermittent contact of the field
wire, and the pulsed loading of the alternator caused the belt to jump. So
far, fixing the wire and replacing the belt have worked fine.

I was there during the entire process, and asked a lot of questions. I never
did get a good answer as to why the problems occurred acutely after the
initial belt change at annual. Also, perhaps he should have looked at the
connections to the alternator first rather than jump to the conclusion that
the voltage regulators were fried, or that the alternator was bad.

However, in a professional and cordial working relationship, I deferred to
his knowledge and experience.
(I hate it when patients come to me and demand a minimally invasive hip
replacement, even though they are 5'2" and weigh 300lbs, or that they want a
specific brand or type of hip replacement because they read about it on the
internet, even though it might be the wrong choice for them)

Anyway, it seems to be working so far. Next, I have to fix the radar.

"Travis Marlatte" wrote in message
t...
If I followed your posts correctly, the last corrective action was
repairing a corroded wire and that seems to have solved the problem, is
that correct?

Disclaimer: I am not an A&P.

I am a part of every repair decision made to my plane. I respect and trust
my mechanic. He does good work and is well respected by a lot of people.
But I know that I am but one, thankfully infrequent customer and he has
other distractions. If the explanation doesn't make sense to me, the
repair doesn't get done until it does. It's a classroom for me and I want
to learn. If I go along with a goose chase, I consider it as much my fault
as my mechanic's. Sometimes, a goose chase is the only approach. Sometimes
it's the easiest. Rarely is it the cheapest. As long as I go into it eyes
wide open, I'll accept the consequences.

The sequence of your events don't seem right. It throws a belt. The theory
is that crankshaft vibrations are causing it. That seems like the least
likely cause but, OK. Replace the belt. It gets thrown again. Why does the
diagnosis now change to be regulators and alternators. That seems to
indicate wild guessing - and, in fact - fickle, wild guessing.

Unless you threw him the keys and said something like, "I don't care what
it costs, just fix the problem," you deserve a break. My mech usually
splits the labor cost of goose chases until we catch the goose. If he
declares the problem but then has to re-fix and re-fix, he bites the
bullet.

If this is your regular mechanic and you don't want to cause a scene, just
remind him of it over the next couple of repairs and see if you can coax
some good will out of him.

-------------------------------
Travis
Lake N3094P
PWK

"Viperdoc" wrote in message
...
It is belt driven off the accessory case. One possible explanation was a
sticking crankshaft counterweight. However, the engine has not shown any
indications of vibrations, such as smoking rivets, cracked baffling, etc.

However, until the new belt was installed, there had never been any
problems with the electrical systems.

I suspect, but will never be able to prove, was that the belt was either
not tightened enough when changed, or the field wire was knocked loose or
kinked, causing the alternator to run intermittently. On inspection after
the fact today, it was corroded.

My standing there watching would not have made any difference- there
would have been no way to tell if the wire was broken, and short of
taking the wrench and tightening the alternator myself there was no way I
could tell if it was loose.

I ran the plane for nearly an hour after the work today, with none of the
same indications, including under a heavy electrical load with lights,
etc in relatively high IMC.

Hopefully, it'll be back to where it was prior to the inspection.

Viperdoc wrote:
First flight after annual, and the alternator light comes on over Lake
Michigan in IMC- left alternator belt thrown, which was replaced at the
annual. Never had any problems with electrics prior to this.

Replace belt, light comes on with application of power or electrical load.

Returned to mechanic- says it could be stuck counterweights on crank shaft
causing vibration that throws belts. I ask- why did this just start after
the annual, with no indication of problems prior to this?

Replace with another new belt- no change. Now note that no voltage is going
to alternator field. Diagnosis- bad voltage regulators (two), possibly bad
alternator.

Both voltage regulators removed and alternator as well. Repair shop says
they are all OK, but replaced brushes anyway.

Working diagnosis is now bad connection at alternator field wire, caused
alternator to run intermittently, and this is what threw belt initially.
Apparently, with intermittent loading of the alternator due to engine
vibrations, these pulsations caused belt to whip and jump off of pulleys.

My guess- wire was bent, kinked during initial belt change, starting cascade
of events.

Two questions: does all of this sound plausible?

Who is responsible for all of the labor, belts, and alternator and voltage
regulator check out?

Should the mechanic who changed the belt initially bear some of the
financial responsibility for this?


Yes, and it sound like it may be time to find a new mechanic.