Need help figuring this one out

[Nico1]

After flying 8hrs one day, I noticed this on cyl #2 (see picture) while pushing the plane back into the hangar. My first thought was a plugged injector. However, during flight I didn't notice anything, and looking through the engine data I found zero evidence of that. Also, note that it is dripping, that to me suggests it likely did not happen in flight.

The following day I visually inspected lines and pressure tested them (flooded cylinders) and saw nothing out of the ordinary. This seems to have been isolated to CYL #2. 

One hypothesis was cool fuel in line expanding with heat on ramp, but to my understanding lines empty out on shutdown.

Taking plane down for annual this week. Would be helpful to have a better idea about what could have caused this to look into at annual. Any thoughts?

 

[Shadrach]

It's obvious that there is an issue with the fuel delivery to cylinder #2. There are several possibilities that come to mind and probably others that I have not thought of.. The line could be compromised. The silver solder at the fitting could be cracked. The injector could be puking fuel through the vent. The cylinder threads could have failed (unlikely). There is no way to tell the precise nature of the problem from the picture.

It's hard to tell if all of the dark areas are fuel staining. You need to enlist the help of an A&P before further flight. It's clear that the aircraft is not airworthy until the cause has been determined and remedied. 

[N201MKTurbo]

Maybe you hit a big blue bug!

[N201MKTurbo]

If it was coming from the injector, I would think there would be fuel stains on the injector, yours looks very clean. 

[N201MKTurbo]

Looking closer, I see the track coming from the injector.

I have often thought this is caused by some resonance in the intake tube that causes a positive pressure pulse at the injector that causes air to flow out of the bleed hole instead of into it. This could blow fuel out with the air. If this is the case, it would probably be at a specific RPM, probably a low RPM.

[Bolter]

46 minutes ago, N201MKTurbo said:

Looking closer, I see the track coming from the injector.

I have often thought this is caused by some resonance in the intake tube that causes a positive pressure pulse at the injector that causes air to flow out of the bleed hole instead of into it. This could blow fuel out with the air. If this is the case, it would probably be at a specific RPM, probably a low RPM.

Isn't there a common problem with using the wrong clamps and clamp location for the fuel delivery tubes that permitted a resonance?  I think they need rubber to get some damping, as well.  

[Ragsf15e]

I’ve had this happen just because the injector loosens itself from its seat.  You’re not supposed to crank it down or use locktite but i had a mechanic tell me they easily come loose.  He used a very small dab of “xx” and the problem resolved.  My new mechanic didn’t want to, but they loosened a bit… he resolved the same way.

[Shadrach]

2 hours ago, Ragsf15e said:

I’ve had this happen just because the injector loosens itself from its seat.  You’re not supposed to crank it down or use locktite but i had a mechanic tell me they easily come loose.  He used a very small dab of “xx” and the problem resolved.  My new mechanic didn’t want to, but they loosened a bit… he resolved the same way.

Yea, not tight at all.  40 to 60 inch pounds. Torque the nozzle to 40 inch pounds then check for the position of the "A" stamped on one of the hex flats on the body. Continue tightening until the "A" points downward within a tolerance of one flat of the hex of the nozzle body. Do not exceed 60 inch pounds.

My case crack occurred about 7 months year after an annual gone bad (nearly $8K and my airplane returned to me in unairworthy condition but that's another story).  After diagnosing the case crack, I got to work removing the engine. The only thing holding injector#1 in place was the B-nut and injector line. It was so loose I could lift it away from the injector port. Intake leak for sure, but no significant fuel staining to be seen.

[Ragsf15e]

So based on what Ross and I just said, check and see if it’s properly torqued, but definitely don’t over torque it.  I bet it stops leaking.  Although Ross said his didn’t leak.  Mine looked just like your picture.

[carusoam]

While you are there…

There is a vent hole in the injector…

If it doesn’t get oriented properly…

It tends to get fuel leaked out of it while flying… (or after shut down…)

Leaving the dark blue stains…

randomly placed around the area…

 

PP thoughts only, not a mechanic… stuff I have seen pics of around here…

Best regards,

-a-

[Guest]

From Lycoming SI1275C,  note the last sentence.  It infers that 60 in minimum torque.

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 fuel bleeding 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 stamped on the hex of the nozzle body points downward.

[EricJ]

In my experience it's tough to get min torque and the stamp in a good place simultaneously, it seems like something is going to break to get the 'A' all the way to bottom, so I set torque and then get it as close as I'm willing without overtorquing it.   Sometimes that's barely a flat before it feels like it's bottomed out.    But it is worthwhile to pay attention to the stamp location to try to get the vent on the upper part of the nozzle.

Now that you've documented the leak with some photos, I'd clean the staining off (with more fuel or some mineral spirits), and then keep a close eye on it to see whether or how fast it reappears.

 

[cliffy]

You can swap nozzles and maybe get a better rotation point for the vent hole.