SkyTec Starter sticking?

[[email protected]]

Hey all. I put a lightweight SkyTec starter on my Cherokee 180 a bit over a
year ago. Recently, I've begun to notice that it's sticking in the ring gear on the
engine for a second or two after startup. I thought it would be like a stock starter
and require some silicone spray, but on a whim I called SkyTec. They said that this
is normal. Since it's a permanent-magnet motor, when you shut off the power it
generates enough juice to keep the solenoid engaged as it spins down. Consequently,
there's a sprag clutch to prevent the engine from driving it in this condition
forever. I'll buy the argument, but recently I've noticed it more.

Any thoughts on this from people who've experienced this? I'm sure that
little gear is haulin' ass with the engine running a 800-1000 RPM on startup. It's
almost a "whiz-rattle"... sprag going bad? Sticky shaft? Worn ring gear? Do I worry
too much... shut up and fly it? :)

Thanks,
-Cory

--

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

[Dude]

I wonder what the overall opinion of SkyTech is? Personally, my advice is to
ignore anything they say.

I have not been happy with my experience. They always have an excuse not to
honor the warranty, and I am tired of sending them money. It seems to be a
scam to get you to keep coming back to them for repairs. Next time, I
intend to igmore the warranty, and just buy a new starter from someone else.





> wrote in message
...
> Hey all. I put a lightweight SkyTec starter on my Cherokee 180 a bit over
> a
> year ago. Recently, I've begun to notice that it's sticking in the ring
> gear on the
> engine for a second or two after startup. I thought it would be like a
> stock starter
> and require some silicone spray, but on a whim I called SkyTec. They said
> that this
> is normal. Since it's a permanent-magnet motor, when you shut off the
> power it
> generates enough juice to keep the solenoid engaged as it spins down.
> Consequently,
> there's a sprag clutch to prevent the engine from driving it in this
> condition
> forever. I'll buy the argument, but recently I've noticed it more.
>
> Any thoughts on this from people who've experienced this? I'm sure that
> little gear is haulin' ass with the engine running a 800-1000 RPM on
> startup. It's
> almost a "whiz-rattle"... sprag going bad? Sticky shaft? Worn ring gear?
> Do I worry
> too much... shut up and fly it? :)
>
> Thanks,
> -Cory
>
> --
>
> ************************************************** ***********************
> * Cory Papenfuss *
> * Electrical Engineering candidate Ph.D. graduate student *
> * Virginia Polytechnic Institute and State University *
> ************************************************** ***********************
>

[Aaron Coolidge]

wrote:
<skytec stuff snipped because 'tin' doesn't auto-wrap columns>

Hi Cory. I have a sky-tec starter sitting in the back of my Cherokee 180
that I bought to replace the Prestolite unit. After buying it, I did some
more detailed reading and found quite a few notes about operation like yours.
As skytec says, the PM motor spins down and generates quite a few volts until
it stops. Because the motor and solenoid are both fed from the starter
contactor the solenoid is the path to ground and it stays pulled in far too
long. The skytec-like design works on cars because the solenoid that kicks
out the pinion gear also energizes the motor but is powered from a different
circuit, so when the solenoid drops out the motor's residual voltage goes
somewhere else. (I suspect that you knew all that.)

The notes that I turned up were from a Grumman Tiger owner that installed
the sky-tec and then had the same "sticky" pinion. The Tiger owner eventually
went back to the Prestolite starter because he was afraid of ruining the ring
gear.

Perhaps sky-tec could have minimized this little glitch with a couple
diodes, and I think it could be completely eliminated with a second starter
contactor to drive the solenoid only. My sky-tec has a heavy external wire
between the solenoid and the motor, so they could be separately driven
easily (in an electrical sense: YMMV paperwork-wise).

The conclusion that I came to was to fix the bendix on my Prestolite starter.
So, now I have a spare sky-tec for when the Prestolite breaks.
--
Aaron Coolidge (N9376J)

[[email protected]]

Interesting. I was thinking a free-wheeling diode might help the situation,
but in order do it, you'd need a true isolator-type diode arrangement. That would
require a diode in the starter motor path... not too great of an idea (WAY too much
current to be reasonable/reliable). The separate contactor for the solenoid would
probably work fine, but the FAA goons are already circling on that one. It's not a
PMA'd replacement if you need to install additional stuff on the airframe. Then it's
an STC and would require more certification and paperwork, etc.

The more I think about it, the more I realize that it was probably a necessary
compromise. Even if you put the contactor *ON* the starter for just the solenoid,
there's no way for it to "know" that the voltage on the starter motor lug is from the
battery vs. the back EMF in the motor. I suppose you could measure the motor current
with a shunt (haha!) or winding, but again... it's more complicated and failure-prone.
The system they have is safe and simple, if a bit inelegant. I doubt the starter gear
could damage the ring gear much since there's no load on it at the time. All it's
doing is free-wheeling the sprag clutch. I suppose it would be good to keep the RPMs
as low as possible until it stops (but then again I do that anyway while the oil
pressure comes up).

Interesting... I think it might even be worth it for the 10 lb weight savings, though.

-Cory


--

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

[B. Jensen]

Cory,

I have had 2 lightweight Skytec starters in the past. I had problems
with both! (one completely ruined my ring gear $$$)
I now use the B&C LW starter on my Lycoming IO-360, and it has been
flawless. My opinion, get rid of the Skytec and get a B&C....from
personal experience.

BTW, if you want to get rid of the sticking shaft on the Skytec, you
must get rid of the small jumper wire on the unit and rewire the ground.

BJ



wrote:

> Hey all. I put a lightweight SkyTec starter on my Cherokee 180 a bit over a
>year ago. Recently, I've begun to notice that it's sticking in the ring gear on the
>engine for a second or two after startup. I thought it would be like a stock starter
>and require some silicone spray, but on a whim I called SkyTec. They said that this
>is normal. Since it's a permanent-magnet motor, when you shut off the power it
>generates enough juice to keep the solenoid engaged as it spins down. Consequently,
>there's a sprag clutch to prevent the engine from driving it in this condition
>forever. I'll buy the argument, but recently I've noticed it more.
>
> Any thoughts on this from people who've experienced this? I'm sure that
>little gear is haulin' ass with the engine running a 800-1000 RPM on startup. It's
>almost a "whiz-rattle"... sprag going bad? Sticky shaft? Worn ring gear? Do I worry
>too much... shut up and fly it? :)
>
>Thanks,
>-Cory
>
>
>

[[email protected]]

B. Jensen > wrote:
: Cory,

: I have had 2 lightweight Skytec starters in the past. I had problems
: with both! (one completely ruined my ring gear $$$)
: I now use the B&C LW starter on my Lycoming IO-360, and it has been
: flawless. My opinion, get rid of the Skytec and get a B&C....from
: personal experience.

: BTW, if you want to get rid of the sticking shaft on the Skytec, you
: must get rid of the small jumper wire on the unit and rewire the ground.

: BJ

This information may have been nice to know when we decided to go with Skytec
last year when our old started broke. It's only a year old, so we'll stick with it
for awhile. It definately starts better and weighs less.

How did the starter hose your ring gear? Did it just never let go? I'm
interested in the "mod" (legal or otherwise... just info) for the sticking shaft. I
haven't looked at it recently to see how it's wired.

-Cory

--

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

[B. Jensen]

Cory,

The ring gear was ruined because the starter gear stayed extended too
long after the engine started. Thus the starter gear broke off the ring
gear teeth.

This mod (bypass) is only for experimental aircraft usage only.
Basically the jumper wire retains residual power for a second or two
after the start switch is released, and cases the starter to stay
engaged. If the jumper wire is removed, then all power is removed
immediately from the starter when the ignition switch is released. I
don't remember the exact wiring mod, but it was easy to do. If you call
Skytec and tell them you have an experimental aircraft, they "might"
give you the diagram.

I learned of it when I took my Skytec to an automotive starter repair
shop, and they were dumbfounded that Skytec used the jumper wire the way
they do. They gave me the correct instructions on how it "should" be
wired. The Skytec is basically a Ford automotive starter, so any
automotive starter repair shop can probably help you. It's been several
years since I switched to the B&C, so I don't remember the details offhand.

VERY happy with the B&C!

BJ


wrote:

>B. Jensen > wrote:
>: Cory,
>
>: I have had 2 lightweight Skytec starters in the past. I had problems
>: with both! (one completely ruined my ring gear $$$)
>: I now use the B&C LW starter on my Lycoming IO-360, and it has been
>: flawless. My opinion, get rid of the Skytec and get a B&C....from
>: personal experience.
>
>: BTW, if you want to get rid of the sticking shaft on the Skytec, you
>: must get rid of the small jumper wire on the unit and rewire the ground.
>
>: BJ
>
> This information may have been nice to know when we decided to go with Skytec
>last year when our old started broke. It's only a year old, so we'll stick with it
>for awhile. It definately starts better and weighs less.
>
> How did the starter hose your ring gear? Did it just never let go? I'm
>interested in the "mod" (legal or otherwise... just info) for the sticking shaft. I
>haven't looked at it recently to see how it's wired.
>
>-Cory
>
>
>

[OtisWinslow]

I had a MagnaFlite on the O-360 on my Tiger and it worked
great.


> wrote in message
...
> Hey all. I put a lightweight SkyTec starter on my Cherokee 180 a bit over
> a
> year ago. Recently, I've begun to notice that it's sticking in the ring
> gear on the
> engine for a second or two after startup. I thought it would be like a
> stock starter
> and require some silicone spray, but on a whim I called SkyTec. They said
> that this
> is normal. Since it's a permanent-magnet motor, when you shut off the
> power it
> generates enough juice to keep the solenoid engaged as it spins down.
> Consequently,
> there's a sprag clutch to prevent the engine from driving it in this
> condition
> forever. I'll buy the argument, but recently I've noticed it more.
>
> Any thoughts on this from people who've experienced this? I'm sure that
> little gear is haulin' ass with the engine running a 800-1000 RPM on
> startup. It's
> almost a "whiz-rattle"... sprag going bad? Sticky shaft? Worn ring gear?
> Do I worry
> too much... shut up and fly it? :)
>
> Thanks,
> -Cory
>
> --
>
> ************************************************** ***********************
> * Cory Papenfuss *
> * Electrical Engineering candidate Ph.D. graduate student *
> * Virginia Polytechnic Institute and State University *
> ************************************************** ***********************
>

[Aaron Coolidge]

B. Jensen > wrote:
: Cory,

: The ring gear was ruined because the starter gear stayed extended too
: long after the engine started. Thus the starter gear broke off the ring
: gear teeth.

: This mod (bypass) is only for experimental aircraft usage only.
: Basically the jumper wire retains residual power for a second or two
: after the start switch is released, and cases the starter to stay
: engaged. If the jumper wire is removed, then all power is removed
: immediately from the starter when the ignition switch is released. I

Cory, it sounds like this is the 2 starter contactor situation like I
mentioned. The jumper wire he's referring to goes between the solenoid and
the PM motor itself.

I liked your idea about a freewheeling diode, but you'd need a series diode
on the input to the PM motor too (to keep the voltage in the PM motor to
freewheeling diode circuit). I wouldn't worry about the current handling
capacity here, 600 A diodes are easy to get, but the Vf of the diode would
probably be like 1.0V. When cranking the voltage at the PM motor is probably
only about 6 or 7 V (piper uses a 6V contactor for the starter) so 1V
lost in the diode is a large fraction of the available power!
--
Aaron Coolidge

[jls]

> wrote in message
...
> Hey all. I put a lightweight SkyTec starter on my Cherokee 180 a bit over
a
> year ago. Recently, I've begun to notice that it's sticking in the ring
gear on the
> engine for a second or two after startup.

A friend of mine installed one of those SkyTecs on his O-200. It was
mounted on the rear accessory case. On final a large chunk of his
crankcase blew out and he damn near didn't make it to the runway. I tore
down the engine and saw all the damage including the rearmost connecting rod
where the big end struck the starter pinion pivot, a device used on the
original starter, and shoved it up through the crankcase. Now how this
pinion pivot came loose from its dowel securing it in place I have yet to
understand.

The FAA, so I understand, is investigating this problem as well as many more
with the SkyTec starter.

[[email protected]]

Aaron Coolidge > wrote:
: Cory, it sounds like this is the 2 starter contactor situation like I
: mentioned. The jumper wire he's referring to goes between the solenoid and
: the PM motor itself.

I found a link to the graphic on Skytec's web page. One that says, "This is
for certified aircraft, this is for experimental." The experimental version is more
like an automotive setup... starter switch runs solenoid. The certified version
switches the main power.

: I liked your idea about a freewheeling diode, but you'd need a series diode
: on the input to the PM motor too (to keep the voltage in the PM motor to
: freewheeling diode circuit). I wouldn't worry about the current handling
: capacity here, 600 A diodes are easy to get, but the Vf of the diode would
: probably be like 1.0V. When cranking the voltage at the PM motor is probably
: only about 6 or 7 V (piper uses a 6V contactor for the starter) so 1V
: lost in the diode is a large fraction of the available power!
: --
: Aaron Coolidge

I'm going to look into modifying the system. By running the jumper wire from
the firewall starter relay's *input* to run the starter solenoid as well, that would
accomplish the same thing. A big current diode could then free-wheel the motor by
itself (no need to be in series... use the starter solenoid contactor for that). I've
contacted Skytec to see if they've every field-approved such a modification. I
understand why they don't do that for all the installations. It would have to be
tested/certified on every airframe/engine combination. If they rig it just enough to
work adequately as the one they replace, they can PMA it and it automatically works on
everything. It may not be optimal, but it works.

We'll see how it goes.
-Cory

--

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