UnPossible

UnPossible

Well Known Member
Hey - I've ran my engine several time now, and have found a slow fuel leak at the FT-60 (Red Cube) fuel flow transducer.

I have removed the transducer and the nipples, cleaned everything up, goobered the fittings up with Permatex #2, and reassembled it a couple of times only for the leaks to remain.

The fittings only seem to leak when the engine is running. If I pressurize the fuel system with the fuel pump, I am not seeing any leaks.

I'm about 99% sure that I did not overtighten the fittings, as I just took them snub, they added about 1/2 a flat of additional rotation.

Does anyone have any idea as to what could be the problem?

Thanks,
Jason
 
Jason----not likely, but look for a crack in the treads. The red cubes are alot thicker that the older transducers that would crack if you overtightened the AN fittings. Tighten them down. The NPT threads seal by the thread taper, so a good sealer is required.

Tom
 
From the install manual:

DO NOT EXCEED a torque of 15 ft. lbs. or screw the fittings tighter than two full turns past hand tight, whichever happens first.
 
Walt---I'm thinking Jason took them to snug and alittle bit, and doesnt have enough torque on the fitting. I agree with you.
Tom
 
TS Flightlines said:
Walt---I'm thinking Jason took them to snug and alittle bit, and doesnt have enough torque on the fitting.Tom
Click to expand...

That's what I was thinking too, most folks have a tendancy to under torque pipe fittings hence the torque for this comes in as a handy reference.
 
TS Flightlines said:
Walt---I'm thinking Jason took them to snug and alittle bit, and doesnt have enough torque on the fitting. I agree with you.
Tom
Click to expand...

Tom - I think you are right.... I think I was afraid of over Torqueing them... I took out the Red Cube and went out and bought a deep well 5/8" socket that will fit the fittings.

Looking at the instrucitons I have, they say not to torque over 25 ft lbs. I set my torque wrench for 25 ft lbs, and the fittings both spun a coupe of full rotations or more beyond where I had them before the torque wrench clicked off.....

Really hoping that this fixes my fuel drip issue..... guess we'll know tomorrow evening.

Thanks,
Jason
 
Red Cube fuel leak

A leaking nipple was the cause of my fuel smell issue in my RV-10.
The nipple was bottomed out in the red cube fuel meter and no amount of torque could seal the weeping leak.
I Pro Sealed it in, problem solved.
 
N427EF said:
A leaking nipple was the cause of my fuel smell issue in my RV-10.
The nipple was bottomed out in the red cube fuel meter and no amount of torque could seal the weeping leak.
I Pro Sealed it in, problem solved.
Click to expand...

If the fitting was actually bottomed out, then either the fitting or the transducer housing is defective. Nothing wrong with using pro-seal, but it should not be used as a "band aid" for another problem.
 
Snug tight?

I've been doing fuel lines recently and decided to use the snug tight and one flat turn method for the aluminium fittings. Then I checked them using the recommended torque for aluminium fittings, and found them apparently way under-torqued - but so much so that I was worried I was damaging the threads when I pulled them up tight using a spanner and electronic fish scale to get the recommended torque.

Walt, you said not more than two turns past finger tight, which sounds about what I found using measured torque. But what is the definition of `snug-tight'. I assumed snug tight meant not much more than finger tight and so couldn't understand why the two methods were giving such different results.
 
No Band aid

In my case, after removing the cube from the tunnel and thoroughly inspecting both nipple and the threads on the red cube I decided to glue them in.
I do agree that if a nipple bottoms out way too early or simply because the threads are galled or other cause, I would certainly not use Pro Seal to band aid the problem. I was dealing with a leak that produced mere fumes or a tiny bit of a weep at worst and this despite having used Tite Seal thread lube and
properly torqued the nipple.
For those considering Pro Seal on fittings, they can quite easily be removed again as Pro Seal holds little shear value.
 
Looks like the fuel leak is gone! I ran the engine for a few minutes over lunch today and no signs of any drops, drips, etc could be seen.... only a handful of items left before I am ready for my AW inspection
 
Very good Jason! Reinspect during your Phase on, and recheck the B nuts on all the hoses I made for you. You should be good for engine run in.
Tom
 
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