PA24 Comanche - alternator belt "flipped" in flight

[SBC News]

1962 PA24 just annualed and a new alternator belt was fitted as prop was
removed. The new belt looks different from the old, but the part number (I
am told) was supposed to be matched/equivalent. The new belt has "teeth" as
it were. The old one was just a standard tapered belt with smooth surfaces.
On a 3 hour flight back to base the belt flipped over. It now has the teeth
facing outwards. It is probably lucky it did not break.
Fixing the problem will require removing the prop unless it is the correct
belt but was somehow not correctly adjusted. (It was the correct way around
on pre-flight and tension seemed correct too.)
Has anyone come across this new belt, and had any similar problems? To my
mind, we just need a belt that looks like the old one. I suspect they are
not compatible, but the mechanic says that according to part numbers they
are.
Any info, appreciated.

[[email protected]]

On Jul 10, 7:30 am, "SBC News" > wrote:
> 1962 PA24 just annualed and a new alternator belt was fitted as prop was
> removed. The new belt looks different from the old, but the part number (I
> am told) was supposed to be matched/equivalent. The new belt has "teeth" as
> it were. The old one was just a standard tapered belt with smooth surfaces.
> On a 3 hour flight back to base the belt flipped over. It now has the teeth
> facing outwards. It is probably lucky it did not break.
> Fixing the problem will require removing the prop unless it is the correct
> belt but was somehow not correctly adjusted. (It was the correct way around
> on pre-flight and tension seemed correct too.)
> Has anyone come across this new belt, and had any similar problems? To my
> mind, we just need a belt that looks like the old one. I suspect they are
> not compatible, but the mechanic says that according to part numbers they
> are.
> Any info, appreciated.

Different manufactureres make their belts differently. That
"toothed" belt is more flexible and generates less heat, so it lasts
longer. Most likely the belt wasn't tight enough, or the alternator is
seizing up, or it's overloaded because the voltage regulator is
failing, or the engine vibrates too much.

Dan

[John[_9_]]

On Jul 10, 10:09 am, wrote:
> On Jul 10, 7:30 am, "SBC News" > wrote:
>
> > 1962 PA24 just annualed and a new alternator belt was fitted as prop was
> > removed. The new belt looks different from the old, but the part number (I
> > am told) was supposed to be matched/equivalent. The new belt has "teeth" as
> > it were. The old one was just a standard tapered belt with smooth surfaces.
> > On a 3 hour flight back to base the belt flipped over. It now has the teeth
> > facing outwards. It is probably lucky it did not break.
> > Fixing the problem will require removing the prop unless it is the correct
> > belt but was somehow not correctly adjusted. (It was the correct way around
> > on pre-flight and tension seemed correct too.)
> > Has anyone come across this new belt, and had any similar problems? To my
> > mind, we just need a belt that looks like the old one. I suspect they are
> > not compatible, but the mechanic says that according to part numbers they
> > are.
> > Any info, appreciated.
>
> Different manufactureres make their belts differently. That
> "toothed" belt is more flexible and generates less heat, so it lasts
> longer. Most likely the belt wasn't tight enough, or the alternator is
> seizing up, or it's overloaded because the voltage regulator is
> failing, or the engine vibrates too much.
>
> Dan


Another thing to consider is the alignment of the alternator pulley
and the ring gear of the engine. Misalignment can contribute to a
belt coming off or wearing out very quickly. If the belt flipped it
must have been very close to coming off altogether. Alternator
vibration should be considered too, are the bearings good on the
alternator. In any event I would consider this belt trashed and get
it replaced. It sounds like your mechanic was being conscietous
enough to trace applicabilty and supersedure of part numbers rather
than go down to auto zone and get close enough.

John Dupre'

[Bob Noel]

In article >,
"SBC News" > wrote:

> 1962 PA24 just annualed and a new alternator belt was fitted as prop was
> removed. The new belt looks different from the old, but the part number (I
> am told) was supposed to be matched/equivalent. The new belt has "teeth" as
> it were. The old one was just a standard tapered belt with smooth surfaces.
> On a 3 hour flight back to base the belt flipped over. It now has the teeth
> facing outwards. It is probably lucky it did not break.
> Fixing the problem will require removing the prop unless it is the correct
> belt but was somehow not correctly adjusted. (It was the correct way around
> on pre-flight and tension seemed correct too.)
> Has anyone come across this new belt, and had any similar problems? To my
> mind, we just need a belt that looks like the old one. I suspect they are
> not compatible, but the mechanic says that according to part numbers they
> are.
> Any info, appreciated.

Another possible cause of 'flipping" is if the pulley is worn enough for
the bottom of the belt to touch the bottom of the V in the pulley.

--
Bob Noel
(goodness, please trim replies!!!)