ALL FIXED! See below for details.
Thanks to everyone for suggestions on repair or replacement of my 914 turbo
servo
with the broken wiper. I learned more than I ever wanted to know about this
system; here are some notes to make your life easier and cheaper for when you
have a similar problem!
First, I bought a used 914 servo through eBay as a quick fix in case other, more
time-consuming searches failed. I didnt use this servo and now have it as a
spare. Per another contributors suggestion, I also purchased a used Kawasaki
Ninja ZX10R ZX1000J exhaust valve servo motor 21174-0005 through eBay for a lot
less money ($25). Confirming one of the comments I received, this
Japanese-manufactured
Kawasaki motorcycle device appears to be a drop-in replacement for
the 914 servo, other than having a hexagonal rather than round pulley. That
is, the Ninja servo appears to have the same wiring, the same case, the same
circuit board, and critically, the same gear and wipers. Im also keeping this
part as a spare. There are plenty more on eBay for less than $35, or new for
about $300 on the web, which is still about $200 less than the Rotax-supplied
part (warning: different part number!)
As one person pointed out, my broken wiper may have been the result of a
manufacturing
defect. Maybe so. However, when I bought the plane from the builder
in California in 2018, the engine only had about 200 hours over the last
12-years,
and my plane now sits for months in the winter inside a cold hangar in Ohio.
Therefore, it is also possible that the dielectric grease caused the wiper
to stick to the circuit board, initiating a crack one day upon power-up. Im
not impressed by the design of this servo because the servo rotates
bidirectionally,
in one direction the wiper drags, and in the other direction the wiper
plows through the grease, which I picture has putting a lot of force on a small
part. The design must work OK for almost everyone, though.
Ultimately, I installed a gear, including the wipers, that I received from
Ronnie at South Mississippi Light Aircraft (www.flysmla.com). Ronnie had a bag
of failed servos next to his desk and I accepted his offer to pull a good gear
and wiper out of a servo with corroded electronics (the wiper is in perfect
condition). This used gear and wiper work perfectly; the TCU + servo appear to
be self-calibrating upon start-up. It would make too much sense for Rotax to
offer the gear + wiper as a spare part. Unfortunately.
The overall repair isnt too bad only confusing to diagnose for a novice. If the
orange TCU caution light blinks immediately upon power-up, then a sensor or
wiring problem is the likely cause. If the orange caution light comes on for
a second or two (as it should), goes off, and then a few seconds later starts
to blink, then the problem is more likely with the servo (like my problem).
Watch
out for, and dont lose, the 3 mm diameter brass thrust plate on the wire
clamp on the pulley. Also keep the aluminum sleeves in the rubber mounting
grommets,
which may or may not arrive with your used part. The Rotax-Owner website
has an easy-to-follow video about properly adjusting the cable to the waste
gate.
Thanks again to everyone for your advice
--------
N914TX
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=501347#501347
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