Leaky fuel bladders in 1982 M20J

[FlyBoyM20J]

There seems to be a very slow leak inside RH wing somewhat farther out than the sump.  My A&P/IA inspected the exterior and instructed me to check the clamps on the interconnect pipes between the cells.

The bladders in this plane were installed in 2014.  O&N B400F.

Does anyone have a picture indicating how to access these most easily?  I located Terry's (@N6758N) thread for installing bladders in his M20C and I generally believe that I should access from the bottom but any suggestions would be welcome.

Cliff

PS - as it happens, I'm parked on the ramp at KOQN about 50% of the time!

Terry's thread is here:

 

[INA201]

I had a leak/seep where the fuel sender on the right wing attach. One of the front access covers about 40% out from the fuselage. It was an easy and cheap fix. 

[BDPetersen]

The access panels are on top of the wing. The interconnect clamps are inside the cells. I do not envy you. To correctly torque them you need the smallest torque wrench you can find. I’m sure someone will step up with more useful info, but having done my install last spring I recall those clamps were a pain even though it seems they would be straight forward. The thoughts of revisiting them makes me sad. I’m thinking someone posted the drawings for the install here. I recall using them to assist my install.

[Mooneymite]

Over a period of time, the gasket seals may become compressed and seep; in almost 30 years, I only had to re-tighten them once at about the 10 year point.  The clue is, at what level fuel do you get a seep?  The difficulty is that regardless of which bladder has the seep, the "evidence" will travel down the inside of the wing and appear near the wing root, unless your bladder is damaged, they can only seep from the top of a bladder, or an interconnection.  Fixing the seep is simple:  open the top access and tighten the screws on the bladder access.  Even if you decide to just do all the accesses, it doesn't take long.

As @BDPetersenmentions, the interconnections can be difficult to torque.  Hope it is an access, not an interconnect.

[FlyBoyM20J]

10 hours ago, INA201 said:

I had a leak/seep where the fuel sender on the right wing attach. One of the front access covers about 40% out from the fuselage. It was an easy and cheap fix. 

This is a strong possibility...the leak seems to happen only when the right tank is full and I always find the fuel level is down a few inches from the filler cap with the float arm roughly level a few days later.  The leak then seems to slow or cease at that level. 

Cliff

[FlyBoyM20J]

8 hours ago, Mooneymite said:

Over a period of time, the gasket seals may become compressed and seep; in almost 30 years, I only had to re-tighten them once at about the 10 year point.  The clue is, at what level fuel do you get a seep?  The difficulty is that regardless of which bladder has the seep, the "evidence" will travel down the inside of the wing and appear near the wing root, unless your bladder is damaged, they can only seep from the top of a bladder, or an interconnection.  Fixing the seep is simple:  open the top access and tighten the screws on the bladder access.  Even if you decide to just do all the accesses, it doesn't take long.

As @BDPetersenmentions, the interconnections can be difficult to torque.  Hope it is an access, not an interconnect.

No fuel dye is evident on top of wing and the access panels installed in 2104 on top and bottom appear sound and sealed still.  The telltale blue dye is around seams near the flap juncture at the back of the wing about 12" out from the sump...and of course, continues down to the sump (where it drips slightly) and on down to the nearby belly panels.

As I mention above in response to @INA201, I think that this may be a case of a fuel sender gasket since the leak seems to happen most when the tank is full and I find the level of fuel has decreased only a few inches until the float arm is about level after a few days of sitting.  But it doesn't seem to leak quickly past that point.

Cliff

[carusoam]

Cliff,

It starts with pics...

Narrow it down to best locations to look...

Fuel level when it leaks is helpful...

Guessing will be misleading...  fuel does some weird traveling...

Bladders are known for their specific type of leaks... most often faulty interconnects...

Terry is known for his fuel tank skills... including installing fancy fuel floats...

If your tanks only have one fuel level float... and your back seat rug is turning blue... and you get the whiff of old plane smell every time you open the cabin....

• Fuel sender gasket
• rubber hose connector on the fuel line, below the sender gasket

PP thoughts only, looking for pics...

Best regards,

-a-

 

[Marauder]

Since you have a J, I would look at several locations. Make sure the seal at the fuel filler is intact. There is sealant between the fuel filler base and the top of wing but the seal underneath the wing and on the bladder seal is the one that should be checked. If it is leaking, fuel won’t show up on the wing but could flow down the bladder and underneath.



Another area to check is the outer fuel sender seal. There is a cork gasket that could be leaking. The inner fuel sender would leak into the cockpit and you would smell it there.




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[FlyBoyM20J]

I had a look at this today but needed to get the fuel out of the bladders, so didn't get the access panels open (other than the outermost one next to filler cap).  There was no evidence of seeping at that access port. 

Also, after sitting for almost 2 weeks in the hangar after being filled to the top, this wing ended up still having approx. 23 gallons.  It would seem the leak is near the top of a cell, since the apparent low level is reached soon after filling and the leak seems to stop or slow after that.

I have some exterior photos below.  I'll get borescope pics and open access panels tomorrow. 

I can also say that the problem is a bit unlikely to be the fuel sender since it is affixed to the outermost (and highest) side of the outermost cell.  But I'll open that panel tomorrow, too, so as to view the other side.

Here's the view from the top:

 

And the view of the leaks from bottom.  The outermost leak appears along the line between the middle and innermost cells, roughly along the outer line of the tread paint.

[carusoam]

Seems to be a fair amount of staining around the sump drain...

If the connection to the drain is leaking inside the wing... it may filling the volume up until it escapes the drain holes in the wing...

It would be really helpful to be able to speak with the shop who did the work, if nearby...

Next on the list would be a shop that is familiar with the bladders...

Terry isn’t that far from you... @N6758N See if he checks in...

Unfortunately, gravity can make a leak at the top, show up 24 inches down hill...

Best regards,

-a-

[FlyBoyM20J]

34 minutes ago, carusoam said:

Seems to be a fair amount of staining around the sump drain...

If the connection to the drain is leaking inside the wing... it may filling the volume up until it escapes the drain holes in the wing...

It would be really helpful to be able to speak with the shop who did the work, if nearby...

Next on the list would be a shop that is familiar with the bladders...

Terry isn’t that far from you... @N6758N See if he checks in...

Unfortunately, gravity can make a leak at the top, show up 24 inches down hill...

Best regards,

-a-

Yes, it does leak out at the sump drain but doesn't seem to be originating from there.  The browner stain farther outboard is the first indication of fuel leaking along the wing - the lighting isn't good in this photo, but that is basically goo that flowed with leaking fuel.  It seems to flow downhill from there inside the wing and drip out at the opening around the sump drain...and past that down to seams in belly panels.

As it happens, the cover plate at the sump drain has a cutout that allows one to see the nipple and the hose clamp...and would allow any leaks to drip out immediate at the drain rather than build up.  Also, any leaks that originate elsewhere are likely to make their way down to that point and drip.  The drip isn't constant or even evident, though.  I think that the leak stops after the fuel level drops by 3 or 4 gallons, so that would also rule out the sump connection itself.

I do know the mechanic who installed it for the previous owner.  I talked with the previous owner just yesterday and he recalled that there was some leaking just after the bladders were installed, and that the mechanic had to add some clamps to interconnects.  Unknown which side or which cells.  So there's that anecdote.

I also have met the gents at Griggs (current STC holders) and 76N is not far from my usual routes.  But they are very busy and my local mechanic thought it would be good experience for me to work on this one and report back to him.

Now that I have emptied the cells, I will pull access panels and check for any evidence of exterior seeping.  I hope to see something but failing that, will just retorque interconnect clamps and clean everything prior to refilling to check for leaks.

Cliff

 

[FlyBoyM20J]

Panels opened today.  Borsecoped outermost cell via fuel filler opening.  Looks good so far but there's no indication that the problem is with the outer cell.

Fuel smell inside innermost cabin-side cell chamber, which makes sense given the locations of the leaks on the bottom of the wing. 

No fuel cell access panels show signs of weeping, likely because the installer used Permatex on the cork gaskets. 

Suspect an interconnect clamp on upper or mid pipe between inner (cabin-side) and middle cells.  But...so much Permatex on the cork.  Did not attempt to defeat yet and it's clear I'm going to need replacement cork gaskets at a minimum.

Going to talk to Griggs tomorrow about those.

 

[carusoam]

Various connections to try to see....

1) Air vent tube...

2) air connections at the top of the tank that allows air to travel outwards... towards the wing tips...

3) Fuel connections at the bottom of the tank that allows fuel to run towards the pick-up... inwards...

4) Fill cap...

5) sump drain...

Ideas based on how the sealed tanks work, not actual knowledge of the Griggs fuel cells...

Best regards,

-a-

[Marauder]

Panels opened today.  Borsecoped outermost cell via fuel filler opening.  Looks good so far but there's no indication that the problem is with the outer cell.

Fuel smell inside innermost cabin-side cell chamber, which makes sense given the locations of the leaks on the bottom of the wing. 

No fuel cell access panels show signs of weeping, likely because the installer used Permatex on the cork gaskets. 

Suspect an interconnect clamp on upper or mid pipe between inner (cabin-side) and middle cells.  But...so much Permatex on the cork.  Did not attempt to defeat yet and it's clear I'm going to need replacement cork gaskets at a minimum.

Going to talk to Griggs tomorrow about those.

 

 

The folks at Grigg’s are pretty helpful. I bought the locking low profile caps from them when I was installing my CiES senders. One of the caps had a deformed O ring and they sent me a full kit not just the O ring in question.

 

I have heard of leaks at the interconnect between the inner and middle (or outer if you have the 54 gallon system). One of the challenges with these leaks is that fuel will go everywhere when you fly it. One of my sumps was dripping intermittently. Fuel from that leak was everywhere.

 

And there shouldn’t be any Permatex on any of the gaskets. There is Proseal on the underside of the fuel filler port and may be used elsewhere. Grigg’s should be able to help you figure out what is going on.

 

 

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[FlyBoyM20J]

5 hours ago, Marauder said:

And there shouldn’t be any Permatex on any of the gaskets. There is Proseal on the underside of the fuel filler port and may be used elsewhere. Grigg’s should be able to help you figure out what is going on.

 

Thanks!  I've been to Griggs a couple of times.  Those are some great and talented people. 

I'm pretty sure I'm looking at a good quantity of Permatex No. 3 here.  These bladders were installed by the mechanic used most often by the previous owner...and that mechanic is fond of Permatex No. 3.  You can see the stuff ran down the inside of the fuel sender in the borescope picture, as well.  I would bet that if that particular mechanic installed anything that had a cork gasket, he'd Permatex it up for good measure.

Wonderful guy, though.

The next step is to open the access panels to allow inspection and torqueing of interconnects.  If I had to open only one bladder panel, it would be the inner (cabin side) since that's the chamber with the odor of fuel and barring a perforation at the bottom of the cell, odds are it's an interconnect clamp accessible from that cell.

I'll call Griggs later this morning and ask if they'll sell me a set of cork gaskets.  I already have a full set of CT clamps coming in case I open up a bladder and see something amiss.

Cliff

 

 

[steingar]

Joey Cole told me that the bladders could be pulley's out through he holes they were put in and refurbished in situ for about an AMU.  That was a few years ago, so it might. be more now.

[FlyBoyM20J]

1 hour ago, steingar said:

Joey Cole told me that the bladders could be pulley's out through he holes they were put in and refurbished in situ for about an AMU.  That was a few years ago, so it might. be more now.

There's a bag on eBay right now that was refurbished by O&N, and the pictured receipt shows about 40% of an AMU.   From perhaps 5 years ago.  I'll get mine repaired if necessary but at the moment, I am willing to believe that a single interconnect clamp requires torqueing.  The trick is to access the clamp without damaging the bladder.

I believe I can remove the Permatex-infused cork and with some very careful clean-up, keep things in good shape. 

I just talked to Griggs to order some more gaskets at $20 each.  Arriving in a day or 2.

[FlyBoyM20J]

And...the bladder access panels are open!  The Permatex was not as pervasive as I feared and it was possible to use a plastic putty knife between the gasket and the fuel bladder...no real pressure required and slowly things came apart.

Inner cell:

 

Middle cell:

 

 

Most of the clamps appeared correctly installed except for this one which is on the 1" mid-height pipe between the middle and inner bladders, as seen from inside the middle bladder looking toward the inner (cabin side).

My mechanic will inspect before I move forward. 

Cliff

 

[FlyBoyM20J]

An update for anyone who was wondering: it was indeed the CT clamp on the 1.5" interconnect between B and A cells in the picture above.

Before I corrected this, I talked with Nate at Griggs and he said that clamps on this interconnect in particular are known to come loose over time and that 90% of the time, the only thing they do when faced with a leak in their shop is open up the cells and tighten all the clamps.  They do not try to locate the source of the leak most of the time, as that is not easy and can take a lot of time.

It now looks like this:

[carusoam]

Great follow-up, with pic, FB!

Thanks for sharing the details...

Best regards,

-a-