Well my maintenance work progresses and today I was ready to remove the
in-tank pump I have written about in an earlier thread. It is not long since I
removed it previously when I had a failure of the internal pipe and had to
solder new wires and fit new hose- about three years ago I suspect.
Many of our listers myself included know full well about the insert problem and I figured that since it came out last time and was torqued to spec upon insertion, it should come out OK today- well I got that one well and truly wrong!
First of all I decided it would be best to remove the tank - took a look at the WSM- nothing special about the job and set about it. Supported the underside of the tank whilst removing the cradle, cut the tank vent and return hoses that I planned to replace and removed the delivery line that routes under the tank. Removed the spill collar and the fill port and then undid the top support bolt. figured the tank should now come out - wrong!- it just seemed to be hung there- what the heck! Scratched my head a bit had a coffee and took another look and spotted the problem- there is a vent line from the top side of the main body with a silly big hose that crosses tightly through a bulk head and then fastens at the top of the fill neck [to act as a vent] via a tee fitting with the fuel return line- the WSM mentioned nothing about this . The connection on the tank body is inaccessible, fastened by a clip and not immediately visible- WTF? I then had to wrestle the tank out and everything seemed to get in the way- had to displace the passenger side mid exhaust section some but not too difficult.
So with the tank out and on my work bench I then took a look at the thing and
the the first problem was how to undo the pump from the insert- I figured the
easy way would be to fit a jubilee clip around the collar as I probably should
have done earlier but will come to that a bit later. I cleaned off the 4 nubs
that stick out a bit but that was probably a waste of time as the clamp I had
was wider than the recess it sits over. Anyway to my delight the thing came
undone nigh on effortlessly. Tried to remove the pump once the flange was fully
unscrewed but it did not seem to want to come out so I undid the clamp and out
it came- cannot explain that one- maybe I was just a bit too tentative.
Upon inspection it was clear that the insert had been pulled out about 1mm or so- see pic below.
Insert proud of the boss.
So my next line of thought was "what to do next"? As I started to think about what happened an interesting thought sprung to mind-as I tried to remove the thing the applied force must have pulled the sleeve into the sealing ring thus lifting it to the point where it no longer sealed - I also noticed that after the first drops of residual fuel appeared as I tried to undo it more fuel leaked- this suggested to me that the seal entirely depends on the ability of the pump to pull on the threads and seat on the outer ring of the tank boss. Thus if the clamp enabled me to remove the pump maybe I could push the insert back where it came from and if I did, maybe the external clamp holding the once more correctly positioned insert will enable the seal to pull down on the boss and seal it once more with no other modifications.
I measured the outer diameter of the insert and found that a 34mm socket had more or less the same outer diameter- after careful placement of the socket and a few blows with a rubber mallet the insert popped back. Even more interestingly, it looks as though the boss has a slight overlap of the insert. The pic below shows what it looked like after reseating the insert.
Insert pushed back in
So, considering the above and the fact that the sealing surface of the hub looks pristine, I am now inclined to think that given it locked the insert to get the pump out, maybe with a new seal and the jubilee clip fitted just maybe it will seal once more.
Tomorrow I will test it but in the meanwhile any thoughts appreciated.
Now just kicking myself for not figuring this logic out earlier even though I previously knew about the clamp- just figured that if it was degraded probably better to find out - however, if the hydraulic seal only depends on the insert being held tight then for sure everyone working on their tank should do this mod immediately before touching whatever is fitted inside the boss - ironic that I thought about such before going in and decided against it- lesson learnt on that one!
When my insert migrated, I pulled it out and whipped up some Marine JB Weld.
I coated the insert and pressed it back in place.
Logical thing to do and on my list of possibilities but I am wondering if
anyone has thought about the issue laterally and simply tried to lock the thing
back in position but this time using the obvious clamping force applied when
Logic tells me if I could release the in-tank pump normally after what happened then maybe it will also permit the seal ring to work once more. It is a bit counter intuitive but stranger things have happened.
Fred at this point I would suggest you get some aviation fuel tank sealant
pull the ring out , mark it first. Then put the sealant into the tank grid, then install your insert then add on a proper size Norma clamp to hold the outer edge of the tank tight against the insert. https://www.145.aero/Flamemaster-CS-3204B1-2-AMS-S-8802B1-2-Sealant-p/cs3204b1-2.htm
Or use this solution: https://928srus.com/products/fuel-tank-repair-sleeve-boss-all-928-fuel-tanks-78-to-95
The seal is on the outer lip as noted, JB weld or whatever might help mechanically but not needed for sealing.
The insert wants to go in from the inside, because the sealing surface has a small lip-- it will pull out, but it is very hard to push it back in. So I removed the tank-sender and sent the insert down that hole on a piece of wire as a guide.
Here is the special tool for pulling it in place, from the inside (made from
1/2" plastic electrical conduit IIRC) and a simple slide hammer to pull it in.
Jim & Sue Corenman