CFM56-5C Oil Leak enigma

[Eclipse 400]

Hi folks,

Following lomapaseo (http://www.pprune.org/members/48942-lomapaseo)'s advice, I post my question here!

Now I've got some issue with CFM56-5 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.

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

- 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 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.

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 what do you think!

Thank you very much by advance for your help.

Eclipse

[lomapaseo]

See if this works for you

Hi folks,

Following lomapaseo (http://www.pprune.org/members/48942-lomapaseo)'s advice, I post my question here!

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.

http://fromtheflightdeck.com/MEL/PPRune/CFM56%20Oil%20leak%201.jpg



http://fromtheflightdeck.com/MEL/PPRune/CFM56%20Oil%20leak%202.JPG


http://fromtheflightdeck.com/MEL/PPRune/CFM56%20Oil%20leak%203.JPG



http://fromtheflightdeck.com/MEL/PPRune/CFM56%20oil%20leak%204.jpg


- 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 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.

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 what do you think!

Thank you very much by advance for your help.

Eclipse

[Eclipse 400]

Thanks for your help lomapaseo, I think that some picture are always better than a long monologue as the adage says.

First picture:
During normal operation, the pressurized air (blue arrow) coming from the booster, inter the pressurization tube (In the second picture you can see the real layout of the 4 pressurization tubes). It's purpose is to force the air to enter (via the labyrinth seals) in the forward sump in order to avoid oil to pour out of the sump. Then, oiled air is leaving the forward sump through the centrifugal oil separator and get out of the aft of the engine via the center vent tube.

In an other hand, oil is sprayed on the different bearings to cool and lubricate them.

Second Picture:

Our problem is that when the engine stop, and after 1 to 2 hours, amazingly oil is leaking into the lower right pressurization tube and then (as shown in the third picture) leak in the airstream.

Again, we changed the forward stationnary seal, and the lips of the labyrinths seals but somehow the problem persist. What surprise me is that there is not enough room for oil to fill up. it's really weired.

If you need more precisions, do not hesitate to ask me I will answer with pleasure

[lomapaseo]

Having taken a closer look at your problem, I am quite convinved that it has nothing to do with the labyrinth seals.

While these seals are necessary with the engine running developing pressure balances they mute when no or little airflow is present. What happens to the oil when shutdown, is that simply gravitates to the lowest point. In this case one of those air tubes at the Bottom.

While running the air as well as the oil pump blow-suck the oil out a scavenge at the bottom of the engine and then on to wherever else it's intended to go (pumps, gears, coolers, etc.)

It seems that in your case some oil at the top of the engine has found someplace to hide for a while as the engine is shutdown. Eventually this oil leaks downward by gravity to a path which leads to a bearing jet. Only in this case once it gets there it can't find its way out to a scavenge because the engine is no longer running.

I would stop looking at the bearing compartments/sumps and start looking at the paths of the oil above these areas.

I'm not familiar with all the plumbing on such a complicated beast but anything with oil in it above the bearing sump itself is more suspect than the oil sump and seals itself

[Eclipse 400]

Thanks lomapaseo for your answer.

Yes indeed I agree with you on the fact that labyrinth seals are most likely not our problem in this leak.

However, I've looked in the oil supply "plumbing" as you said :) in order to see if at any point there is any possibility for oil to leak (and of course there are numerous). The problem is if the leak would come from the oil supply tubes, it wouldn't finish it's course in the 8 o'clock pressurization tube. This is still the sobering point of this problem.

But your track is interesting and I will continue to search on it's way.

Thank you again for your help .

[Bye]

Ok had a good look now and most of its pretty clear.

firstly have you checked the o rings on the pressure tube that is showing oil after shutdown.

it is possible as the engine shuts down and cools the tube goes into negative pressure relative to the sump area and may be drawing the oil in past the tube seals.

failing that i am drawn to the oil seperator, not sure on the direct path but oil may be getting onto the shaft and pooling between the front and second seal in the shaft area, taking time to build up to the height needed to the go over the weir effect of the lower tube being radially up the wall so to speak.

it could just be a very slow leak past the labrynth seals, which are notorious for leaking, again as the tube is up a bit from the pool start a slow leak will take time to pool deep enough to go over the weir.

i'll keep thinking but i think it is the front labrynth seal, maybe the running bit is eccentric slightly or the shaft is bent, are the bearings wearing normally.

GB

[Eclipse 400]

firstly have you checked the o rings on the pressure tube that is showing oil after shutdown.

firstly have you checked the o rings on the pressure tube that is showing oil after shutdown.

it is possible as the engine shuts down and cools the tube goes into negative pressure relative to the sump area and may be drawing the oil in past the tube seals.Yes , we checked that when we removed the fwrd stationary seal, they were good.


failing that i am drawn to the oil seperator, not sure on the direct path but oil may be getting onto the shaft and pooling between the front and second seal in the shaft area, taking time to build up to the height needed to the go over the weir effect of the lower tube being radially up the wall so to speak.

it could just be a very slow leak past the labrynth seals, which are notorious for leaking, again as the tube is up a bit from the pool start a slow leak will take time to pool deep enough to go over the weir.In fact, instead of "oil separator" I should rather write "air/oil separator" because its purpose is to separate the oil from the oiled air which creates in the sump. The oil itself is going down by a vertical drain tube.

i'll keep thinking but i think it is the front labrynth seal, maybe the running bit is eccentric slightly or the shaft is bent, are the bearings wearing normally.

Yes we are still looking strongly those points because it seems that they are incriminated in the leak but since we changed them by brand new (stationary seals, labyrinth air seals etc..) and the leak is still occur after engine run, the problem remains.

Thank anyway for your analyse GB.

[Eclipse 400]

Hi every one,

I'm coming back to all of those who were interested in this post to give our conclusion on our leak who give us some serious problem:

First: we had multiple leaks on some engine but only the first one had in fact really leaked importantly. After a lot of dimensionnal corrections applied to the forward stationary seal, and after for engine run, we decided to change all labyrinth seals by new ones, change the sattionary seal aft and rear by a new one. Then at the fifth engine run it was finally over :)

Second: on the other leaks , we still had the leak after the engine run (supposedly because of pressure and/or temperature changement during the engine run, thank you lomapaseo for the advice) but because I hadn't all the pieces of the puzzle because of my position, I had some times incorrect informations. Anyway, the leaks which appeared on others engines weren't that important (I learned it far more too late) and not as important as the first engine leak has been in reality. But as a precaution, engineering department decided to investigate those leak too, thinking that they were all conected.

After those leaks, it have been decided to applied the same workscope to all the leaking engine (which was all sensitive parts replaced by new one like it was the case in the first engine). It tooks a lot of time in order to be able to test all those engines but now the leak is eventually gone.

As a conclusion, the first engine has serious leak cured by replacing the apprently faulty forward stationary seal or labyrinth seals, and the oil coming from the others one in smaller quantity, had leaks related, we think, to overhaul process. By interrogating mecanics, it appears that they used to use Vaseline in large quantity (to large perhaps) during installation of the parts mentionned above, likely causing the vaseline plus perhaps some oil , to leak .

As you can see, we are not 100% positive about what really cause all those event but we can only guess what happended. Today, even if we still have very little oil coming by the 8 O'clock pressu tube now, we're considering this as totally normal.

By the way, I suspect personnaly that we might have some "over mayhem" after the first engine leak concerning the 4 other leaks, pushing perhaps some high ranking participant to emphasised a litlle bit to much, darkening the situation and finally creating what we used to call a "storm in a teacup".

Thank you for those who tried to help me here and elsewhere :ok: and don't hesitate to ask me anything if you want more precisions.

Good by!