CFM56-5C Oil Leak enigma

[Eclipse 400]

Hi folks,

I'm reading quite a lot of interesting things on the forum since some times. Thanks for your profesionnalism.

Before posting, I've done some searches on the forum but I couldn't find out my answer.

Now I've got some issue with CFM56-5C engines we had to overhauled recently and I was wondering if I could have your point of view on that because the problem is tricky:

During test bench, oil leak consumption is totally normal and we have no oil leak. Then when the test end, about 1 to 2h after we have an oil leak coming from the forward sump. 8 o'clock pressurization tube (Aft looking forward) of the N°3 bearing forward stionnary air/oil seal. The problem is we're talking of only 50 to 100 cl of oil but still a leak.

What puzzle me is the fact that :
-oil can't agglomerate enough in the forward sump to pour first through the forward staionnary seal, and then through 8 o'clock pressurization tube into the booster,
- VBV doors either side of 6 o'clock strut are quite greasy (even some droplets)
- using black light, IGV are barely greasy proving that the leak wasn't there when the engine was running,
- after booster and N1 & 2 bearing support assembly removal, the N°3 bearing forward air/oil seal circular runout was good.
- no leak from the aft sump coming between LPT shaft and N2 tube.

After first testbed refusal, we changed :
- the N°3 bearing forward air/oil seal (brand new)
- the aft stationnary air oil seal (which by the way wasn't faulty)
But we still have the leak after the test.

I'm running out of solution for this sobering enimga so if you have some ideas, I'm interested and curious to read your view.

Thank you very much by advance for your help.

[lomapaseo]

Sounds like thermals and a stack problem either rotating (not likely) or stationary part tolerances.

You CMF56 service tech should sort this out via a telecom to home base.

[Eclipse 400]

Thank you lomapaseo for your advice.

The problem is our CFM56 tech support have worked on the problem too, send request to CFMI (who have never seen this problem before apparently ...) but they all don't know where and why the leak appear.

I was wondering by asking the question here if someone have already have those kind of problems.

Thank you anyway.

[lomapaseo]

Try the Engineers and Technicians forum on this site for their experience.

[Bye]

not that hot on the CFM56 TBH but with a drain down of the oil after 1-2 hours i'm trying to visualize where the oil could be CF'ing out to or holding under some residual pressure.

I'm with Lomapaseo TBH sounds like a Thermal effect on a seal clearance which may be overheating due to hot soak after shut down.

can you post a section of the engine for us non CFM chaps to look at, indicating where you are finding the oil.

[Eclipse 400]

Thank you , Yes I wanted to put an image but I first didn't success to do so. But now I do:

http://www.servimg.com/image_preview.php?i=653&u=11276132http://www.servimg.com/image_preview.php?i=653&u=11276132http://www.servimg.com/image_preview.php?i=653&u=11276132(Sorry even by doing exactly as shown in example ( by putting http://my adress and at the end), my image don't appear ...

So in the draing above we have:

- Yellow: the forward sump. This area is during the engine run always full of oil coming from oil nozzles. The purpose is, as you can imagine, to lubricate and cool the bearings (in blue),
- Green: the famous forward stationnary air/oil seal. His purpose is to close the the area of the forward sump via labyrinth seals (each sides of the pressuriation tube)
-Red : the rear stationnary seal: same prupose.

In the plan, the pressurization tube has been represented at 12 o'clok in order to appear on the plan but in reality there is 4 pressu tubes at 10 and half, 1 and half, 4 and half & 7 and half (which wouldn't have been represented otherwise). And so the oil leak is coming from the 7 o'clock (aft looking forward) after engine stop.

Really weired because once again, oil can't agglomerate at those locations.

I will follow your advice lomapaseo thank you I thought that it was the only part of the forum dedicated to technical discutions.