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How to repair fuel tank outlet? Can it be done?

 
Old 08-05-2016, 11:43 PM
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Jim Chambers
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Default How to repair fuel tank outlet? Can it be done?

Tank began to leak at the outlet. Attempted to remove the strainer to replace the seal. Slight torque on the fitting increased the leak. More torque and the strainer began to spin in the bung without coming out. Apparently the leak was between the threaded insert and the tank.

I have read some posts suggesting repair is possible with epoxy but have not found specifics. Search has demonstrated this is a common problem.
What can be done other than replace with a used tank (which could have the same problem). I will drop the tank. Then have to figure out how to remove the strainer. Then repair if possible. Help!
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Old 08-05-2016, 11:58 PM
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Fast forward to the 12 minute mark.

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Old 08-06-2016, 12:09 AM
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I'd pull the strainer and insert together and separate them on the bench. Once you have the insert separated from the tank use an appropriate epoxy to bond the insert back into the tank. Tighten a hose clamp on the outside of the plastic "hub" the insert goes in. This will help the epoxy seal evenly. Anecdotal reports seem to indicate this method has a 50/50 chance to work.

Mike
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Old 08-06-2016, 01:08 PM
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My repair using JB weld lasted almost 4 years before I developed a leak. I repaired again and its been my daily driver for the last 8 months since.
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Old 08-06-2016, 01:21 PM
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Jim Chambers
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Jim, you used JB Weld to reattach the threaded insert? Or to seal from the outside?
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Old 08-07-2016, 11:36 AM
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I used JB weld around the insert and as I pushed it in and rotated slightly to ensure a consistent coating the excess smooth it on the outside. The strainer seal needs a flat smooth surface to mate to one threaded in so you need to be judicious with any material you put on the outside.

have a plastic lip formed around the outside edge of the insert during vulcanization that makes inserting the insert almost impossible. I carefully trimmed that lip to allow the insert to go back in and still have some bonding material on the surface.

The JB weld did eventually turn soft creating the leak I had last Christmas.

I used "Seals All" this last time around. We will see if the marketing holds up to the performance of the JB weld.
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Old 08-08-2016, 07:33 AM
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I spun my insert shortly before exporting the car back home, so I sealed up the leak with PC11 as in the video. Never leaked a drop for several years. When I got the car home I found a replacement tank and fitted that. Was advised to apply anti-seize, and only tighten filter enough to stop it leaking - this was not much tighter than hand-tight.
I pulled the filter+ insert out as a unit, and it was not as hard as in the video to separate them. Gave the tank to another 928'er who basically refitted the insert as in the video, and hasnt looked back. He actually ran a wire through the tank top hole and out through the bottom, and slid the insert along that so he could pull it into place from the inside.
jp 83 Euro S AT 56k
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Old 08-09-2016, 10:10 AM
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Use JB Weld Marine Weld. Holds better. Use a little anti seize on the threads. Clamp around the outside of the hub with a thin water hose clamp. Don't over tighten the strainer. Just enough so it doesn't leak. Should last a good long time.

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Old 08-09-2016, 11:34 AM
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Originally Posted by jwillman View Post
...
have a plastic lip formed around the outside edge of the insert during vulcanization that makes inserting the insert almost impossible. I carefully trimmed that lip to allow the insert to go back in and still have some bonding material on the surface.
This lip is actually the sealing surface for the o-ring on the strainer/in-tank pump. Removing the lip will make it harder to seal.

What worked for me was to pull the strainer out along with the threaded metal insert (i.e. past the lip), then persuade the insert off of the strainer on the bench.

Then get the insert back in place from the inside, try to line it up with the original "witness marks" in the knurling (but not critical). Use a narrow clamp to reinforce the plastic, then reassemble with new o-ring. JB-weld or similar is helpful but not required IMO, the sealing is between O-ring and the lip in the molded plastic fitting.

More info:

https://rennlist.com/forums/928-foru...l#post11611542

Scroll down to post #3 for pictures.

The narrow clamp, in my view, is essential-- plastic is flexible and not nearly strong enough for threads, hence the metal insert. But then the weak point is then between the tank and insert. Adding a metal reinforcement to a plastic fitting is common practice, and clamping plastic between two metal parts-- the insert and an outer band-- is stronger yet. But you need to preserve the original sealing surface.
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Old 08-09-2016, 12:04 PM
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Jim Chambers
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Very interesting Jim. I now have the insert/strainer on the bench and soaking with PB Blaster prior to separating. I had assumed that my leak problem was between insert and tank opening rather than a failed seal between strainer and tank. I now see what you describe by looking at the insert/strainer interface. My seal had totally disintegrated. The insert only enters into the mix from the fact that it spins when attempting to remove the strainer, making removal impossible.

I am having difficulty comprehending the process for insertion of the insert from the inside. Also,
do I understand you to say you use no adhesive but simply clamp the insert in place and then reinstall the strainer? I suppose if that is the case, the only risk is a spinning insert upon next removal of strainer (which I hope to never do again!) if the clamp does not hold it. I am thinking that the "insert from inside approach" could not be done with a coating of epoxy on insert and/or tank orifice.
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Old 08-10-2016, 01:22 AM
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Originally Posted by Jim Chambers View Post
Very interesting Jim. I now have the insert/strainer on the bench and soaking with PB Blaster prior to separating. I had assumed that my leak problem was between insert and tank opening rather than a failed seal between strainer and tank. I now see what you describe by looking at the insert/strainer interface. My seal had totally disintegrated. The insert only enters into the mix from the fact that it spins when attempting to remove the strainer, making removal impossible.

I am having difficulty comprehending the process for insertion of the insert from the inside. Also,
do I understand you to say you use no adhesive but simply clamp the insert in place and then reinstall the strainer? I suppose if that is the case, the only risk is a spinning insert upon next removal of strainer (which I hope to never do again!) if the clamp does not hold it. I am thinking that the "insert from inside approach" could not be done with a coating of epoxy on insert and/or tank orifice.
Tank can stay in car but is an opportune time to remove and dissemble and clean it out anyway as well as derust and repaint the tank cradle.

Remove the fuel level sender from the tank. Vaseline or grease on the internal threads of the sleeve, to keep the opeoxy off the threads. JB Weld or Devcon epoxy applied to the inside of the tank where the sleeve sits. Thread a piece of stiffish wire through the top of the tank and out of the strainer opening. Thread the sleeve onto the wire then attach a washer (same diameter as sleeve) or similar to the wire behind the sleeve. Make sure there is enough wire left behind the sleeve to still poke out of the top of the tank once the sleeve is in place. Pull wire through tank along with sleeve and use the wire to pull the sleeve into position once sleeve seated in place withdraw wire from the top of the tank.

IIRC if you have noodly arms like me you can actually reach the sleeve position inside the tank allowing you to position the sleeve by hand then use some form of string/wire pulling tool to pull the sleeve into place.

I get what Jim is saying regarding epoxy not being needed because the seal is between the flange on the tank and the flange on the strainer. However when I had to do this job the flange on the tank got badly mangled during the process of removing the irrevocably joined sleeve and internal fuel pump.
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Old 08-10-2016, 02:38 AM
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Originally Posted by Jim Chambers View Post
...The insert only enters into the mix from the fact that it spins when attempting to remove the strainer, making removal impossible.
Right, the insert provides the threads to tighten the seal against the lip-- but when it seizes to the strainer and spins, then nothing comes apart without some serious pulling.

Originally Posted by Jim Chambers View Post
I am having difficulty comprehending the process for insertion of the insert from the inside. Also,
do I understand you to say you use no adhesive but simply clamp the insert in place and then reinstall the strainer? I suppose if that is the case, the only risk is a spinning insert upon next removal of strainer (which I hope to never do again!) if the clamp does not hold it. I am thinking that the "insert from inside approach" could not be done with a coating of epoxy on insert and/or tank orifice.
I didn't use any sealer, most types won't stick to plastic but it would provide a gap-filler to make things a bit more secure. No harm at all in using some JB weld or something else, just be sure the surface of the lip (or whatever is left of it) is clean and smooth.

The insert-from-inside trick is shown in pics 4-5-6 in this thread:
https://rennlist.com/forums/928-foru...l#post11611596

First, thread a piece of stiff wire (e.g. 12-14 gauge house wire) from tank-sender opening through the strainer fitting. Then drop the insert down the wire, it will fetch up on the inside of the fitting (pic #4). Line it up straight with a finger or two, with the help of the special tool in pic#5.

Now it just needs to be pulled into position, I made a makeshift slide-hammer from special tool #5 and some threaded rod, pic #6. Catch the coupling part of special tool #5 on the inside end of the insert, and bang it outwards with the threaded rod-- nuts and washers at each end. Or use a real slide-hammer with a hook attachment. Jon's ideas are good also.

It is not that tight of a fit-- which of course is the problem-- but you need something to tap it into place from the backside. Same basic problem as getting a clutch pilot bearing out of the end of a crankshaft.
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Old 08-10-2016, 04:17 PM
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Jims & Jon --

Discussion at this point is how to keep the threaded sleeve lined up with the face of the tank nozzle, so we aren't depending on the o-ring seal to do any more than fit snug against the face of the tank lip. I like the threaded rod "puller", and we'll put a socket or maybe a pipe nipple in the outside to keep the sleeve aligned square to the tank face as the sealant for the sleeve sets.

Looking ahead, I see an opportunity to make a two-piece insert that has o-rings at the inside and outside of that tank lip, plus a "locating" o-ring around a sleeve to keep the sleeve concentric. At the same time, the inside nipple could be sized to use a much-less-costly GM or Ford fuel strainer, and possibly a similar-issue in-tank pump for cars that need them. The outer nipple could be sized to use a hose with the same ID as the pump inlet, so the special Porsche hose could be replaced with more common straight hose. I'll get dims from Jim C's tank and sketch some pieces for discussion.
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