Understanding fuel servo maintenance

On 19 Nov 2006 08:11:59 -0800, "Robert M. Gary"
wrote:


Viperdoc wrote:
I've had two fuel servos repaired on two different engines- My impression is
that the parts are adjusted to insure adequate fuel flow, which is the
desired end result. I can not imagine how a spring would get stiffer with
time- perhaps the diaphragm became more compliant. Why not ask your mechanic
or the fuel shop?

Mechanic doesn't understand fuel servos (in fact, I've yet to ever find
an A&P who understands them from other than a theory point (since
they're aren't allowed to work on them anyway)). I got an anonymous
call from the fuel shop, I don't actually know who worked on it.
My real question is "is replacing the spring considered a repair issue
or an adjustment issue"?

-Robert

Not sure what you are looking for here, honestly. If you cannot
discuss this with the person/facility that did the repair, contact
another facility.

http://www.gnaircraft.com/access.htm

Just one company that has been working on them for a long time. Just
be sure you have a clearly defined question that you want an answer
to. I.E. if you know specifically what part was replaced, your
specific servo p/n and your symptoms prior to repair.

http://www.precisionairmotive.com/

Dig into this site for the list of product support & warrany repair
centers-I can't post a "link" to that page, but G & N is on the list.

I "understand" Bendix/RSA servos just fine, but have no idea what you
are asking, I've never repaired one. Maybe you need to talk to someone
who repairs them every day.

TC

wrote:
On 19 Nov 2006 08:11:59 -0800, "Robert M. Gary"
wrote:
Not sure what you are looking for here, honestly. If you cannot
discuss this with the person/facility that did the repair, contact
another facility.

I guess I was hoping for smarter people here. Whenever I speak to
the fuel shops (or any A&Ps) all I get is "it was too rich, it needed
to be dialed down". My concern is still "why was it running on day 1
and didn't run day 2". I don't think the thing can "unadjust itself" in
one day. However, I'm not sure if changing out the spring is just a
'readjustment' or a fix for a problem. Sadly, none of the fuel shops I
spoke to even know how to answer that. I guess they're just in the mode
of correcting what they see wrong, not necessarily finding a root
cause. In my line of work we spend weeks in classes learning how to do
RCA (finding actual root causes of things, not just fixing the signs of
the problem). When I mention root cause I get blank looks from the fuel
techs or A&P. The best I get back is "install it and try it". However,
that means I need to put a certain number of hours on it before I feel
good about flying the family and the Boy Scouts. Also, each R&R is
costing me about 10 hours of A&P time.

-Robert


http://www.gnaircraft.com/access.htm

Just one company that has been working on them for a long time. Just
be sure you have a clearly defined question that you want an answer
to. I.E. if you know specifically what part was replaced, your
specific servo p/n and your symptoms prior to repair.

http://www.precisionairmotive.com/

Dig into this site for the list of product support & warrany repair
centers-I can't post a "link" to that page, but G & N is on the list.

I "understand" Bendix/RSA servos just fine, but have no idea what you
are asking, I've never repaired one. Maybe you need to talk to someone
who repairs them every day.

TC

On 20 Nov 2006 10:52:00 -0800, "Robert M. Gary"
wrote:


I guess I was hoping for smarter people here. Whenever I speak to
the fuel shops (or any A&Ps) all I get is "it was too rich, it needed
to be dialed down". My concern is still "why was it running on day 1
and didn't run day 2". I don't think the thing can "unadjust itself" in
one day. However, I'm not sure if changing out the spring is just a
'readjustment' or a fix for a problem. Sadly, none of the fuel shops I
spoke to even know how to answer that. I guess they're just in the mode
of correcting what they see wrong, not necessarily finding a root
cause. In my line of work we spend weeks in classes learning how to do
RCA (finding actual root causes of things, not just fixing the signs of
the problem). When I mention root cause I get blank looks from the fuel
techs or A&P. The best I get back is "install it and try it". However,
that means I need to put a certain number of hours on it before I feel
good about flying the family and the Boy Scouts. Also, each R&R is
costing me about 10 hours of A&P time.

-Robert


Understood. Seriously.

If I'm not careful, my personal "ouiji board" will steer this towards
a rant, been enuff/too much of that here lately.

You want to correspond further (possibly gaining more info, but also
risking a rant) drop me an e-mail.

TC

10 hours? And you said OK to that? I was hoping you were a little
smarter than that ;-)

We had our servo replaced at annual and were charged 2 hours for the
R&R. Did you look at what's involved it the R&R? Not much. And yes the
servos are adjustable. Matter of fact one of the ways you can tell it is
time for a new one is when the adjutsment screw is turned all the way
out and no more adjustment is left.

The servos are good for about 1000 hours before they need rebuilt so if
yours has around that many hours than you probably just wasted your
money trying to nickel and dime the situation instead of just rebuilding
yours.

As far as "needing" to know the root cause of everything, does it really
matter? Do you need to know why you have a headache before taking some
asprin? :-)

Jon Kraus
'79 Mooney 201
4443H @ UMP


Also, each R&R is
costing me about 10 hours of A&P time.

As far as "needing" to know the root cause of everything, does it really matter? Do you need to know why you have a headache before taking some asprin? :-)

Sometimes it can save your life.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

Jon Kraus wrote:
10 hours? And you said OK to that? I was hoping you were a little
smarter than that ;-)

They had to pull all the intake and exhaust stacks to gain access.

The servos are good for about 1000 hours before they need rebuilt so if
yours has around that many hours than you probably just wasted your
money trying to nickel and dime the situation instead of just rebuilding
yours.

I do have 1000 SFNEW on this engine and servo. I'm surprised the FAA
doesn't have an AD requiring service severy 1000 hours if the units are
this prone to just flat out fail like that.

But this seems to imply that these are very dangerous parts. If this
servo had "unadjusted" itself in flight I would probably be in the
hospital right now. I just got lucky that it "unadjusted" itself during
runup (the engine quit and would only run if the mixture was held right
at idle cut off, moving the mixture forward would flood the engine
out). Engine ran great one day, engine failed the next.

As far as "needing" to know the root cause of everything, does it really
matter? Do you need to know why you have a headache before taking some
asprin? :-)

I just need to know that its not going to need to be adjusted again
while I'm flying over the Sierras. I like to fly to some very remote
areas of Mexico. Taking a 2 week donkey ride back to the states through
the desert isn't appealing.


-Robert

On 11/21/06 09:23, Robert M. Gary wrote:

[ snip ]


I just need to know that its not going to need to be adjusted again
while I'm flying over the Sierras. I like to fly to some very remote
areas of Mexico. Taking a 2 week donkey ride back to the states through
the desert isn't appealing.

I hear you can ride on the tops of trains ;-\



-Robert

Jon Kraus wrote:
10 hours? And you said OK to that? I was hoping you were a little
smarter than that ;-)

We had our servo replaced at annual and were charged 2 hours for the
R&R.

Just curious, did you already have the lower cowl dropped during the
R&R? If you went through the lower cowl vs. removing the intake stacks
I usually get charged 3 hours just to drop and return the lower cowl. I
can usually do it myself but it takes me 4-5 hours myself.

-Robert