On Jan 30, 10:21 pm, (John_F) wrote:
Do NOT use WD40!! WD40 turns into a stickey mess in a short period of
time. After using WD40 in a few months or less the bendix will stick
and will not extend to engage even though the starter spins. Use 50%
motor oil and 50% STP or straight 50w motor oil NOT WD40.

Lycoming says to use only silicone spray lube on the starter
drive. It will not attract dust as all other lubes will, and dust plus
oil equals sticky sludge. You might need to remove the starter, take
the drive out and clean it thoroughly.
Many starting problems involve old contactors, both the master
contactor and starter contactor, and both are usually found on the
firewall or battery box. These things aren't airtight, and oxygen gets
into them and causes oxidation of the copper contact disc and teminal
heads. That oxide is not a good conductor and will result in some
resistance, which causes more heat, which accelerates the oxidation.
We have to regularly replace contactors on our six flight school
airplanes, and when we buy another (used) airplane we usually replace
both of them right off simply because of their age. A low-time
contactor will still be oxidized because of the years since
manufacture. A bad contactor can ground an airplane far from home and
cause us expensive repairs. A new battery is just a waste of money,
trying to fix the wrong problem.
Another problem: old ignition switches. The contacts in these are
lubricated with a grease that hardens with time and lifts the contacts
apart. Arcing occurs and the switch soon burns out. There are ADs
against some of these switches.
There is no contactor inside the Prestolite starter on a Lyc.
There IS a 200-hour brush inspection requirement, because worn brushes
or commutator will cause starting problems. And a lousy contactor or
tired battery will result in much longer crank cycles, which heats the
starter and melts the solder joining the armature wires to the
commutator segments, or will melt the segment bonds and they'll be
thrown out. End of $450 starter. See how an old $25 contactor can
cause many more problems?

The OP mentioned turning off the radios and other stuff to try
to start. Radios should be turned off before turing off the master at
the end of a flight and left off until the engine has been started
again. Some radios have no voltage spike protection. Some aircraft
have a diode across the master contactor coil to shunt the spike, some
don't, and some of those diodes are busted. Some starter contactors
have diodes, many don't. The starter has no diode. Some aircraft have
a relay that opens the supply to the avionics during the start, many
don't.
Any contactor has a coil, the starter has several coils, and
the alternator has a field coil. All coils create a sharp voltage
spike when the current is cut off. Switching the master off, the
alternator off, or releasing the start switch all create that spike
(I've measured the master contactor's spike at 600 volts) and those
expensive radios aren't all built to put up with it, especially
considering that the spike creates an electron flow in the wrong
direction through the bus. That's why many aircraft have an avionics
master switch (that has no coil involved). The rest should have the
radios shut off before shutdown.

Dan