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<< Lancair Builders' Mail List >>
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Don,
I too had my starter solenoid stick twice. The second time it cost me the
starter because I didn't catch it in time. Simply tapping the solenoid with a
wrench freed the solenoid each time. After the second incident I replaced the
starter solenoid and dissected the old one. Removing the crimped on lid reveals
the inner workings without destroying it functionality. The power studs change
into a large square cross sections inside the housing. The contact area of this
square block is quite large. Electrical contact is made when the solenoid
plunger pulls down a large disc that looks like a really thick area washer made
of copper against the surface of the square studs. The disc is free to rotate
and makes contact in a different spot each time. It was easy to tell where the
solenoid had been temporarily welded shut. It was also apparent that the disc
was making contact at the corner of the square stud and not across the entire
surface. It looks as though over tightening a nut on the stud can cause a
minute amount of rotation of the stud leading to a line contact instead of the
intended area contact.
While the starter solenoid is welded shut, the master solenoid acts both as the
master and starter solenoid and so I was a bit concerned about it having
received some arcing damage during troubleshooting of the starter solenoid. At
the next annual (condition inspection) I pulled the master solenoid apart and
found it to be identical internally except for the coil wiring and possibly the
coil itself. The contact surfaces were in much better shape than those of the
starter solenoid. This only makes sense since the master is generally closed
before the big current rush of a starting sequence. The largest current the
master should normally encounter is that caused by the hydraulic pump starting
up-not a small load, but significantly smaller than a starter.
To prevent another starter from going up in smoke, I have installed an LED next
to the starter button that illuminates if voltage is applied to the starter. I
also check the battery voltage after engine start but before bringing the
alternator on line. The voltage should return to 12.x. If it is down at 9 or
10 volts you have a problem. I am also going to start replacing starter
solenoids as a routine maintenance item (every 200 hours perhaps). There was
absolutely nothing unusual about the two start sequences in which the solenoid
stuck, so I now assume it is stuck every time until instrument indications say
otherwise.
Chris Zavatson
N91CZ
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