Fuel Stains on injectors...

[mooneym20d]

Hopefully this is not an issue. I just noticed fuel stains on my fuel injectors just below, what appears to be vents on the injectors. Not too familiar with the engineering of the injectors and not sure if they are original lycoming or GAMI. Probably original. Anyway, I did notice fuel percolating from these vents immediately after shutdown. 

Is this an issue?

[jetdriven]

I noticed the fuel staining on the injectors as well, right after cleaining them.  I ws rathr alarmed and after a google search, Sacramento Skyranch says that clogged injectors cause this. Now I just cleaned them like crazy ten hours before and my GAMI spread essentially  went from over 1 GPH to near zero. NFW they are clogged.   Walter Atkinson, the APS and GAMI guy says the staining occurs after shutdown. You do hear fuel boiling in the lines, and it must go somewhere. Out the injector screen.  So now, I monitor it, but am not alarmed.

 

YMMV.

 

"The blue stains are NOT from an injector being clogged.  They occur after shutdown!  Some of the excess fuel left in the fuel lines boils/vaporized out through the screen of the injector.  This is normal and not something to be the least bit concerned about."

from: http://www.cessnaowner.org/forums/topic.html?id=15475

[mooneym20d]

Thanks Byron. I must say, you are certainly a wealth of info regarding Mooneys. 

[KSMooniac]

My experience is the same as Byron's... non-clogged factory injectors and I have stains around them.  If you listen carefully after shutdown, you can hear the fuel burbling sometimes.  It might be interesting to clean the stains off some time, and then immediately de-cowl the plane after touch down and try to see it happening.

[mooneym20d]

I have seen the percolating fuel. Worried me the first time I saw it.

[Shadrach]

Per Lycoming - the injectors are supposed to be installed with the air-bleed in the 12:00 position (facing up) and the "A" stamp on the wrenching hex flat facing down.  It seems that this installation detail is occasionally missed, this will contribute to "boil out" after shut down...

[jetdriven]

Ross: I remember reading Lycoming SI 1275C. I reinstalled #2 and #3 in the same holes, and swapped #1 and #4.  The paragraph reprinted below from the SI says if the injector are mounted horizontally, align the "A" flat with the bottom. I'm not sure that this means, IO-360 injectors are mounted at a 30 degree angle from vertical.  Any ideas? Comments?

 

Step 6.  Reassemble the nozzles as follows:
LW­18265:  In  normally  aspirated  engines  where  the  nozzles,  P/N  LW­18265  (see
Figure  2),  are  installed  horizontally,  particular  attention  must  be  paid  to  the
identification marks stamped on one of the hex flats on the nozzle body. This mark
is  located  180°  from  the  air  bleed  hole  and  must  appear  in  the  lower  side  of  the
nozzle  to  assure  that  the  air­bleed  hole  is  on  top in  order  to reduce
from  this  opening  just  after  shutdown.  To  ensure  nozzle  is  correctly  torqued,
tighten the nozzle to 60 in.­lbs. torque. Then continue to tighten until the  letter or
number on the nozle points downward.

 

 

 

[Shadrach]

Quote: jetdriven

Ross: I remember reading Lycoming SI 1275C. I reinstalled #2 and #3 in the same holes, and swapped #1 and #4. The paragraph reprinted below from the SI says if the injector are mounted horizontally, align the "A" flat with the bottom. I'm not sure that this means, IO-360 injectors are mounted at a 30 degree angle from vertical. Any ideas? Comments?

Step 6. Reassemble the nozzles as follows:

LW­18265: In normally aspirated engines where the nozzles, P/N LW­18265 (see

Figure 2), are installed horizontally, particular attention must be paid to the

identification marks stamped on one of the hex flats on the nozzle body. This mark

is located 180° from the air bleed hole and must appear in the lower side of the

nozzle to assure that the air­bleed hole is on top in order to reduce

from this opening just after shutdown. To ensure nozzle is correctly torqued,

tighten the nozzle to 60 in.­lbs. torque. Then continue to tighten until the letter or

number on the nozle points downward.

I never knew that the exact angle was 30 degrees, just that they were angled. I don't really understand why the bleed hole would be a path of lessor resistance than the injector orifice, but we get bluing nonetheless. I can only speculate that it's because vaporized fuel rises and that having the bleed holes on top (12 o'clock when looking at the injector) allows fuel to escape in the form of vapor as opposed to vapor condensing and dripping out through the bleed hole if it were on the bottom. Any other explanations would be welcomed...