Maintenance questions

[JJS]

Okay, the Cherokee 140 annual is nearly finished. Compressions are 80, 80, 80, & 78 over 80 after 5 1/2 years and
650 hours of mostly autogas use.

So far everything looks very good except for two things. My A&P IA was inspecting the propeller spinner back plate
and was turning the prop real slow by hand as he did so. He noticed that the impulse coupler on the left mag wasn't
clicking. He turned it a little faster and it works fine. Tried it slow again and sometimes... no clicky. Since
I've had no starting problems, he suggests I just keep flying it unless it begins to give trouble. The mags won't be
due for overhaul for at least another year. My question is: Is there a slow death type "normal" failure mode in
which progressively harder starts occur or do impulse couplers usually fail suddenly and leave you stranded? I
really don't want to throw away money. On the other hand I'd rather not get stranded after dark at an airport away
from home with no mechanics around or parts to be had.

Question #2 The nose strut is not leaking, but there is a spot in which the chrome plating is beginning to blister.
It is hard to see and is low on the strut where it would take some extremely hard braking or a big bump, (or one of
my not so good landings, come to think of it) to get the top portion of the strut to pass over it. Eventually I
suspect, it will need attention. Is it still possible to have these struts rechromed? A Google search turned up a
post from 2002 listing these guys:

Industrial Plating Co. Inc.
1300 Clydesdale Avenue
P.O. Drawer 2365
Anniston, AL 36201
800-525-6408
Fax 256-237-1579

FAA Repair Station # IPBR525K

Can anyone who has had this done in the not to distant past recommend additional business possibilities and perhaps
relate a cost to do it?


--
Joe Schneider
8437R
(Remove No Spam to Reply)



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On 11-Aug-2005, "JJS" <jschneider@remove socks cebridge.net> wrote:

> My question is: Is there a slow death type "normal" failure mode in which
>
>progressively harder starts occur or do impulse couplers usually
> fail suddenly and leave you stranded? I really don't want to throw away
> money.
>On the other hand I'd rather notget stranded after dark at an airport away
> from home with no mechanics around or parts to be had.


A "sudden" failure would most likely be a fracture of the impulse coupler
itself, which does not seem to be where your problem is leading. I'd deal
with it if and when you begin having starting difficulties. However, please
remember that this advice may be worth no more than you are paying for it.
--
-Elliott Drucker

[[email protected]]

: So far everything looks very good except for two things. My A&P IA was inspecting
the propeller spinner back plate : and was turning the prop real slow by hand as he
did so. He noticed that the impulse coupler on the left mag wasn't : clicking. He
turned it a little faster and it works fine. Tried it slow again and sometimes... no
clicky.
I would be a bit concerned on that. There are AD's against some mags' impulse
couplings (like mine... O-360 with Bendix). Basically, the little tabbies that are
supposed to catch and load the spring get worn. Also, there is a bad type of rivet
that holds them on the impulse coupling. If the pivot point on the catch tabs are
worn, it could be binding enough once in awhile so gravity won't drop them where they
need to catch. If these couplings fail and fall apart, they'll drop a bunch of little
steel pieces in the accessory housing and likely jam up the gears. Since important
things like the camshaft run on those, it could ruin your day.

Even if they aren't the type with ADs on them, I'd take the mags off an have a
looksee. It doesn't take that long to take them off and look. Also, it's typical for
only one mag on the Cherokees to have a impulse coupling. Does yours have one on
both?

: Question #2 The nose strut is not leaking, but there is a spot in which the chrome
plating is beginning to blister. : It is hard to see and is low on the strut where it
would take some extremely hard braking or a big bump, (or one of : my not so good
landings, come to think of it) to get the top portion of the strut to pass over it.
Eventually I : suspect, it will need attention. Is it still possible to have these
struts rechromed? A Google search turned up a : post from 2002 listing these guys:

I don't know about rechroming, but the worst thing I can think of that would
happen would be a bit more wear on the rubber O-ring seals on the struts. They're not
that tough to replace either... just a bit messy. I would be a bit concerned about
any heating that may have to happen to have it rechromed. I don't know anything about
the process, but losing the heat treatment on them could be bad. I'd probably see
what some fine sandpaper on the blistered chrome would do. Just make sure it doesn't
rust afterwards.

-Cory

--

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

[[email protected]]

On Thu, 11 Aug 2005 21:03:51 -0500, "JJS" <jschneider@remove socks
cebridge.net> wrote:

snip
>due for overhaul for at least another year. My question is: Is there a slow death type "normal" failure mode in
>which progressively harder starts occur or do impulse couplers usually fail suddenly and leave you stranded? I
>really don't want to throw away money. On the other hand I'd rather not get stranded after dark at an airport away
>from home with no mechanics around or parts to be had.

Typically, there is a light spring on each fly-weight that holds it in
the engaged position to "cock" the coupling. When the engine starts,
and the magneto RPM increases, the heavy end of the f-w overcomes the
spring and keeps it from cocking and clicking. When the engine is
running, tension from the main coiled flat spring that "fires" the
coupling is what holds the coupling in the static straight-up (opposed
to retarded for start) timing position.

If the coupling does not cock-and-fire, you are trying to start your
engine with standard timing (advanced 20-25 degrees BTDC). If the flat
spring breaks, you have retarded "start" timing in flight-that is not
a good thing. As another poster mentioned, the riveted assembly can
come apart-that is not a good thing either.

It's your airplane, you decide what you want to do.

snip

>Industrial Plating Co. Inc.
>1300 Clydesdale Avenue
>P.O. Drawer 2365
>Anniston, AL 36201
>800-525-6408
>Fax 256-237-1579
>
>FAA Repair Station # IPBR525K
>
>Can anyone who has had this done in the not to distant past recommend additional business possibilities and perhaps
>relate a cost to do it?

Yes-it is much cheaper than purchasing a new strut, but it is not
inexpensive. It is the only facility that I am aware of that has the
capabilities (and the approval) to grind and hard-chrome aircraft
struts.

It will come back looking like brand-new.

Regards;

TC

[dave]

The coupler was failing on my left mag. Starting the plane became more
and more difficult particularly in cold weather. Why take a chance on
being stuck somewhere?
Dave
68 7ECA
JJS wrote:
> Okay, the Cherokee 140 annual is nearly finished. Compressions are 80, 80, 80, & 78 over 80 after 5 1/2 years and
> 650 hours of mostly autogas use.
>
> So far everything looks very good except for two things. My A&P IA was inspecting the propeller spinner back plate
> and was turning the prop real slow by hand as he did so. He noticed that the impulse coupler on the left mag wasn't
> clicking. He turned it a little faster and it works fine. Tried it slow again and sometimes... no clicky. Since
> I've had no starting problems, he suggests I just keep flying it unless it begins to give trouble. The mags won't be
> due for overhaul for at least another year. My question is: Is there a slow death type "normal" failure mode in
> which progressively harder starts occur or do impulse couplers usually fail suddenly and leave you stranded? I
> really don't want to throw away money. On the other hand I'd rather not get stranded after dark at an airport away
> from home with no mechanics around or parts to be had.
>
> Question #2 The nose strut is not leaking, but there is a spot in which the chrome plating is beginning to blister.
> It is hard to see and is low on the strut where it would take some extremely hard braking or a big bump, (or one of
> my not so good landings, come to think of it) to get the top portion of the strut to pass over it. Eventually I
> suspect, it will need attention. Is it still possible to have these struts rechromed? A Google search turned up a
> post from 2002 listing these guys:
>
> Industrial Plating Co. Inc.
> 1300 Clydesdale Avenue
> P.O. Drawer 2365
> Anniston, AL 36201
> 800-525-6408
> Fax 256-237-1579
>
> FAA Repair Station # IPBR525K
>
> Can anyone who has had this done in the not to distant past recommend additional business possibilities and perhaps
> relate a cost to do it?
>
>

[DL]

If the impulse coupler spring breaks, you have, at best, a dead mag. If you
don't notice the subtlety in flight (as I once did) you will notice it as a
dead mag on your next run-up.

"JJS" <jschneider@remove socks cebridge.net> wrote in message
...
> So far everything looks very good except for two things. My A&P IA was
> inspecting the propeller spinner back plate and was turning the prop real
> slow by hand as he did so. He noticed that the impulse coupler on the
> left mag wasn't clicking. He turned it a little faster and it works fine.
> Tried it slow again and sometimes... no clicky. Since I've had no
> starting problems, he suggests I just keep flying it unless it begins to
> give trouble. The mags won't be due for overhaul for at least another
> year. My question is: Is there a slow death type "normal" failure mode
> in which progressively harder starts occur or do impulse couplers usually
> fail suddenly and leave you stranded? I really don't want to throw away
> money. On the other hand I'd rather not get stranded after dark at an
> airport away from home with no mechanics around or parts to be had.
>> --
> Joe Schneider
> 8437R
> (Remove No Spam to Reply)
>

[[email protected]]

There are ADs against many mags, some of them dealing with
impulse failures. Get the mechanic to check for any that apply to this
mag.
Corrosion and sludging often cause sticky impulse couplings.
Neither are good, especially the corrosion, which can cause spring
breakage and power loss. Mags on infrequently-flown airplanes, or those
mags that haven't been off for a long time, definitely need checking.

Dan

Dan

[JJS]

> If the coupling does not cock-and-fire, you are trying to start your
> engine with standard timing (advanced 20-25 degrees BTDC). If the flat
> spring breaks, you have retarded "start" timing in flight-that is not
> a good thing. As another poster mentioned, the riveted assembly can
> come apart-that is not a good thing either.
>
> It's your airplane, you decide what you want to do.
>
> snip
>
>>Industrial Plating Co. Inc.
>>1300 Clydesdale Avenue
>>P.O. Drawer 2365
>>Anniston, AL 36201
>>800-525-6408
>>Fax 256-237-1579
>>
>>FAA Repair Station # IPBR525K
>>
>>Can anyone who has had this done in the not to distant past recommend additional business possibilities and perhaps
>>relate a cost to do it?
>
> Yes-it is much cheaper than purchasing a new strut, but it is not
> inexpensive. It is the only facility that I am aware of that has the
> capabilities (and the approval) to grind and hard-chrome aircraft
> struts.
>
> It will come back looking like brand-new.
>
> Regards;
>
> TC

TC, Thanks. I was hoping you'd comment. I called my A&P IA today and visited with him. We will pull the mag and
inspect the coupling closely. All of the mag AD's have been been complied with all along since I've owned the
airplane. I appreciate the comments on the repair station as well.



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[JJS]

"DL" > wrote in message ink.net...
> If the impulse coupler spring breaks, you have, at best, a dead mag. If you don't notice the subtlety in flight
> (as I once did) you will notice it as a dead mag on your next run-up.

May I ask how you detected a broken impulse coupler spring in flight, DL? I might learn something here.



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[BTIZ]

depending on the Mag, there is a service AD for the magneto on the impulse
coupler fly weight tolerances (or something like that). I'd ask about the AD
and ask if your mag requires that inspection. I think it is due at each
annual.

BT

"JJS" <jschneider@remove socks cebridge.net> wrote in message
...
> Okay, the Cherokee 140 annual is nearly finished. Compressions are 80,
> 80, 80, & 78 over 80 after 5 1/2 years and 650 hours of mostly autogas
> use.
>
> So far everything looks very good except for two things. My A&P IA was
> inspecting the propeller spinner back plate and was turning the prop real
> slow by hand as he did so. He noticed that the impulse coupler on the
> left mag wasn't clicking. He turned it a little faster and it works fine.
> Tried it slow again and sometimes... no clicky. Since I've had no
> starting problems, he suggests I just keep flying it unless it begins to
> give trouble. The mags won't be due for overhaul for at least another
> year. My question is: Is there a slow death type "normal" failure mode
> in which progressively harder starts occur or do impulse couplers usually
> fail suddenly and leave you stranded? I really don't want to throw away
> money. On the other hand I'd rather not get stranded after dark at an
> airport away from home with no mechanics around or parts to be had.
>
> Question #2 The nose strut is not leaking, but there is a spot in which
> the chrome plating is beginning to blister. It is hard to see and is low
> on the strut where it would take some extremely hard braking or a big
> bump, (or one of my not so good landings, come to think of it) to get the
> top portion of the strut to pass over it. Eventually I suspect, it will
> need attention. Is it still possible to have these struts rechromed? A
> Google search turned up a post from 2002 listing these guys:
>
> Industrial Plating Co. Inc.
> 1300 Clydesdale Avenue
> P.O. Drawer 2365
> Anniston, AL 36201
> 800-525-6408
> Fax 256-237-1579
>
> FAA Repair Station # IPBR525K
>
> Can anyone who has had this done in the not to distant past recommend
> additional business possibilities and perhaps relate a cost to do it?
>
>
> --
> Joe Schneider
> 8437R
> (Remove No Spam to Reply)
>
>
>
> ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
> News==----
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> Newsgroups
> ----= East and West-Coast Server Farms - Total Privacy via Encryption
> =----

[JJS]

There are ADs against many mags, some of them dealing with
> impulse failures. Get the mechanic to check for any that apply to this
> mag.
> Corrosion and sludging often cause sticky impulse couplings.
> Neither are good, especially the corrosion, which can cause spring
> breakage and power loss. Mags on infrequently-flown airplanes, or those
> mags that haven't been off for a long time, definitely need checking.
>
> Dan

All the AD's are complied with. I use Aeroshell 15W - 50 semi-synthetic oil, changed every 50 hours and will be
surprised if things are gunked up or corroded but I might get shocked. I put over 100 hours on the Cherokee this
year including the 2000 nm cross country trip to Canada and back. I've averaged somewhere between 80 to 120 hours
per year on her for the 7 years I've owned her and have installed rebuilt mags once. We are going to pull the mag in
question and take a closer look. Thanks for confirming what my conscience was already subtly telling me to do.



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[JJS]

> I would be a bit concerned on that. There are AD's against some mags' impulse
> couplings (like mine... O-360 with Bendix). Basically, the little tabbies that are
> supposed to catch and load the spring get worn. Also, there is a bad type of rivet
> that holds them on the impulse coupling. If the pivot point on the catch tabs are
> worn, it could be binding enough once in awhile so gravity won't drop them where they
> need to catch. If these couplings fail and fall apart, they'll drop a bunch of little
> steel pieces in the accessory housing and likely jam up the gears. Since important
> things like the camshaft run on those, it could ruin your day.
>
> Even if they aren't the type with ADs on them, I'd take the mags off an have a
> looksee. It doesn't take that long to take them off and look. Also, it's typical for
> only one mag on the Cherokees to have a impulse coupling. Does yours have one on
> both?

All AD's are complied with on my airplane. I just have the one impulse coupling on the left mag. We'll pull the mag
and look hard at the area you describe. Thanks Cory.



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JJS <jschneider@remove socks cebridge.net> wrote:
: > Even if they aren't the type with ADs on them, I'd take the mags off an have a
: > looksee. It doesn't take that long to take them off and look. Also, it's typical for
: > only one mag on the Cherokees to have a impulse coupling. Does yours have one on
: > both?

: All AD's are complied with on my airplane. I just have the one impulse coupling on the left mag. We'll pull the mag
: and look hard at the area you describe. Thanks Cory.

I thought that too. My IA is particularly thorough on finding ADs on not only
the aircraft, but all the accessories, too.

IIRC, the AD against the Bendix mag impulse coupling is just to look for wear
on the catch pin, not the pivoting teeth and their associated pivot pin. What you
describe sounds like it could be that pivot point binding somehow... not part of the
AD (again, IIRC).

-Cory

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

[Mike Spera]

Given the possible consequences, I would pull both mags and have then
looked over. Why? As you said, you risk a failure away from home at an
inconvenient place and time (at night, on Sunday, on a field with no FBO).

Why both? If you have another year to go before overhaul time (which I
trust you are doing every 500 hours), and one is flaky, there is a
chance that whoever did them last time was less that perfect.

But, that's just me. I take both Slicks in every 400-500 hours. We
usually wind up replacing one and overhauling the other. The next time
around, the new one gets overhauled and the overhauled one gets
replaced. Usually costs around $550 or so. Cheap piece of mind for me.

I have no experience with Bendix mags. So, if you have them, others will
need to chime in.

Good Luck,
Mike

> He noticed that the impulse coupler on the left mag wasn't
> clicking. He turned it a little faster and it works fine. Tried it slow again and sometimes... no clicky. Since
> I've had no starting problems, he suggests I just keep flying it unless it begins to give trouble. The mags won't be
> due for overhaul for at least another year. My question is: Is there a slow death type "normal" failure mode in
> which progressively harder starts occur or do impulse couplers usually fail suddenly and leave you stranded? I
> really don't want to throw away money. On the other hand I'd rather not get stranded after dark at an airport away
> from home with no mechanics around or parts to be had.

[DL]

Long time ago ('82). As best I can remember, slightly unusual EGT readings
and maybe a slight roughness (Continental O-470). The next time I was
directly over an airport I reduced power and did a mag check (at 9000 feet).
One mag was dead. I switched back to both and announced that we would be
landing at that airport, where the spring got replaced.

Another time, after a fuel stop, in doing the runup, one mag was dead. That
turned out to be a defectively manufactured Bendix capacitor (terminal
crimped over insulation) that had worked for almost a year. Later, that day
in talking with my daughter (who was 10, then, and had been riding in the
right front seat on the previous leg), she mentioned that she had noticed
some slight roughness in the flight leg that preceded the failed mag check.
I agreed with her. Apparently, it had not not been pronounced enough to
lead me to do another one of those "enroute" mag checks.

"JJS" <jschneider@remove socks cebridge.net> wrote in message
...
>
> "DL" > wrote in message
> ink.net...
>> If the impulse coupler spring breaks, you have, at best, a dead mag. If
>> you don't notice the subtlety in flight (as I once did) you will notice
>> it as a dead mag on your next run-up.
>
> May I ask how you detected a broken impulse coupler spring in flight, DL?
> I might learn something here.
>
>
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> Newsgroups
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[JJS]

"DL" > wrote in message nk.net...
> Long time ago ('82). As best I can remember, slightly unusual EGT readings and maybe a slight roughness
> (Continental O-470). The next time I was directly over an airport I reduced power and did a mag check (at 9000
> feet). One mag was dead. I switched back to both and announced that we would be landing at that airport, where the
> spring got replaced.
>
> Another time, after a fuel stop, in doing the runup, one mag was dead. That turned out to be a defectively
> manufactured Bendix capacitor (terminal crimped over insulation) that had worked for almost a year. Later, that
> day in talking with my daughter (who was 10, then, and had been riding in the right front seat on the previous
> leg), she mentioned that she had noticed some slight roughness in the flight leg that preceded the failed mag
> check. I agreed with her. Apparently, it had not not been pronounced enough to lead me to do another one of those
> "enroute" mag checks.
>
> "JJS" <jschneider@remove socks cebridge.net> wrote in message

>> May I ask how you detected a broken impulse coupler spring in flight, DL? I might learn something here.

Thanks, DL. I ordered a copy of "The Magneto Book" from Sacramento Sky Ranch and should be getting it any time now.
Hopefully it will help me with some of my questions about magnetos and impulse couplers. I didn't realize a broken
impulse spring coupler would disable the mag. Obviously, I've never seen one apart. BTW the A&P IA pulled mine
after I asked him too. He found nothing amiss. All tolerances were acceptable and there was no gunk or corrosion.
He lubricated it and reinstalled it. The Cherokee is back in my hangar waiting on me to reinstall the interior. The
annual is complete except for that and the paperwork.



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