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1. 12:30 PM - Rotax with the blahs (Leo J. Corbalis)
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| Subject: | Rotax with the blahs |
--> Engines-List message posted by: "Leo J. Corbalis" <leocorbalis@sbcglobal.net>
A Kitfox builder asked for info on my problem. Since many people have little experience
with things electric I gave him more advice than usual.
My specific symptoms were a seeming loss of guts. This started around
400 hours.Compression checks both types said the mechanical parts were OK. Occasional
shakes, sort of intermittent, slower climb and cruise, rough running
during approach to landing. Sometimes the "mag" checks were worse than others
but not really bad. A remark by a mechanic that had worked on Rotaxes set me on
the right track. He said that they had a lot of trouble with the very hard stranded
wire that Rotax used, breaking strands and getting intermittent. The result
is marginal electrical power to the ignition module giving weak or missing
sparks
You sound like your electrical knowledge ends at flipping the wall switch
up to get lights. So forgive me if I'm too basic. First get a cheap DIGITAL
Volt/ohmmeter. They are much harder to break. Get at least 2 short test leads
with small alligator clips on the ends. Radio Shack is a good source. Test
each one by clipping to the red and black leads in the lowest ohm setting. should
read zero or less than 1 ohm. Not too gently pull on the wires to the clips.
If any are intermittent, solder them or throw them away. The meter comes with
test probes that have dull points which are OK for some tests but when you
run out hands, use a clip lead for connecting the probe to what you want to test
and use your hands for jiggling the connector or wire while watching the meter.
If the readings jump around you have located the part with broken strands
or a bad connection.
I had a very intermittent partial failure in the red wire that comes out
of the alternator where it enters the 1 pin connector that delivers power to
the ignition module. I disconnected the lead, jumpered the black probe to the
engine. Test this by getting zero ohms when you touch the red probe to another
part of the engine. Shove the red probe between the connector and the plastic
cover on it. Now hole the connector and wiggle the red wire. The meter should
read 4 ohms(this is the resistance of the coil in the alternator or magneto
generator in Rotax speak) (I think, maybe 40 ohms) steadily as you gently move
the wire. If the readings jump around, and a gentle pull causes them to jump
way up or show open, you've found the problem.
Another trick is to get a straight pin hook it to the meter with a jumper wire
and slide it under the plastic cover to make contact with the point being tested.
You can push the pin thru the insulation on a wire to check for voltage or
continuity ( this may make a high resistance contact, OK for voltage checks
but not reliable for resistance checks as it adds false resistanc to the reading.
Now for the fun part, fixing it. Buy AMP brand crimper and parts if
possible. Also get a wire stripper with graduated notches for each wire size.
You will probably have to go to an electronics store other than RS. get the
blue connectors (color wire size) Ask the salesman (sexist) to teach you how
to crimp, using your parts. For wire, I had a high grade test lead. They have
fairly tough insulation and 2 or 3 times the number of strands of wire than the
Tefzel stuff from spruce. These finer strands will flex much more before breaking.
Pomona is a good brand to use. Yes the cost 3 to 5 bucks but do it right.
Test your crimping skill by pulling firmly about 30 pounds to test and get
it right before you leave the store.
Cut off the bad connector, use an inline splice to connect the red
wire to the test lead, cut it about 3 inches long and install a new plug. ( I
got some bullet shaped single male blue connectors from an auto store. This is
easier and more reliable than prying the cutoff plug apart and recrimping it)
Now use small tie wraps to tie all the wires together so that jiggling is minimized.
Last but not least do the other one because mine failed 2 months later.
Leo Corbalis
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