More Skytec starter woes

Hey all... I posted about a year ago about "residual engagement" on a Skytec
starter for my Cherokee 180. At that time, I discovered the poor way that they wired
it for certified aircraft use. Using the alternate wiring (for experimental only)
http://www.skytecair.com/Wiring_diag.htm, this backEMF driving the solenoid could be
eliminated. Since this would require alteration of aircraft wiring, PMA'ing the unit
would be difficult.

NOW, I've run into another problem with my plane. Recently, it has become
harder to start. I had some chipped teeth in the ring gear from awhile back, so I was
just assuming it was finally wearing out. Over the past couple of flights, it will
often "give up" on a compresison stroke and you can hear the starter just "whizz." I
called Skytec and they dismissed my theories that:
- Remaining engaged for a second or so is hard on the ring gear.
- I should try to rewire the system so it cannot do that.
- A broken tooth off the ring gear is causing the dead spot... rather the starter
should be sent back to them for measurement and verification of the sprag clutch and
housing.

Anyone else experience this? I must admit that I was rather put off by the
customer service guy on the phone. His attitude was, "We've got tens of thousands of
these in service, so your problem cannot be due to bad design." Then he went on to
say that a kickback can break the sprag clutch, bend the shaft, or bend the housing,
and that free-wheeling gears after starting is harmless. *Any* design (good or
bad) can stand improvement... especially when regulations limit the design process. I
would imagine that the checkup on our starter won't be covered by warranty either
since it's over 1 year old.

-Cory

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************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

These are not normally troublesome starters. I've had one on my Arrow
for 10 years with no hiccups at all.

Cory,

Over the past couple of flights, it will
often "give up" on a compression stroke and you can hear the starter just
"whizz." I

This is common for several reasons. One is weak battery, two is corroded
connections or terminations somewhere, corroded battery cable (rare), bad
contactors/relays/solenoids, need of lubrication on the post that the little
starter wheel travels on to engage the flywheel and lastly a bad starter.
Of course there can be any combination of the above.

Go on SkyTec's site and do the SkyTec Troubleshoot checklist. Find the drop
in voltage and fix or replace what the problem is.

http://www.skytecair.com/images/Trou...iagram_5.0.pdf

Kobra

That "whizz" sounds like a slipping sprag clutch (Bendix drive). Don't
run into that very often at all on those drives. It was more common on
the old small Continental starter drives, which ran in oil and after a
little wear they would start to slip.

Dan

wrote:
: That "whizz" sounds like a slipping sprag clutch (Bendix drive). Don't
: run into that very often at all on those drives. It was more common on
: the old small Continental starter drives, which ran in oil and after a
: little wear they would start to slip.

Well, I've done a bit more looking. Probably should have done this before I
posted. What I thought was missing teeth on the ring gear is more like worn ones. I
rolled it over today (didn't start it because I hadn't preheated). At least this
time, it sounds like the gear wasn't fully engaging. Between that and the worn teeth,
it seems like it can get shoved back out of the tooth when the load gets high (i.e.
compression stroke).

I'll try to take a closer look this weekend sometime. Plausible theories
include:

- Low voltage causing weak solenoid engagement... voltage will drop even more as the
load goes higher and the starter motor pulls more juice. Most likely theory at this
point, but haven't narrowed it down to battery, master/starter solenoid, or wiring
terminals.
- Slipping sprag clutch.
- Binding on sprag clutch causing partial engagement.
- Bent shaft/housing causing binding.

I've been pretty careful with the battery, although I did let it sit dead
overnight once (left master on). I'm sure that damaged it some, as lead-acid
batteries don't like that at all.... could just be weak. We *have* owned it for over
3 years now.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************