My thoughts.....
I have one weeping rivet in my QB tanks in the same area...Thoughts out there???
Mike,
You have a clear idea of the dynamics involved. For the benefit of those builders who may
have some difficulty understanding the forces at work here, I will attempt to outline the 3
"perfect storm" conditions that must occur at the same time to cause a rivet to "weep."
1. The fuel within the tank enters a breach or more technically, a leak path through the
fillet dam along the rear baffle.
2. Continuing its journey, the fuel then finds an open void hidden somewhere in the
skin/baffle faying surface leading to that weeping rivet hole location.
3. The fuel (or its fumes), now pooled in that open void hidden from view in the faying
surface, then moves on to take advantage of the last bastion of proseal defense which
is the lack of sufficient sealant that should be underneath the manufactured head
of the rivet. As a consequence, the fuel pushes its way through the gap, finally escaping
and leaving its tell-tale blue dye on the surface.
All three points of failure must occur
at the same time to cause a particular rivet hole
location to "weep." If any one of the three failure points had remained intact, the chain
would have been broken and the rivet would not leak. Just fix any 1 of the 3 failure points
and the problem goes away....technically, that is. I say technically because few people are
actually going to completely remove the back baffle just to get at and repair the mating
faying surfaces as described in point
2. Cutting a hole or a series of holes in the rear
baffle to gain access to the inside of the fuel tank so the fillet dam can be repaired is a far
more practical solution for addressing gross leaks.
Now in your situation Mike, you do have options. The easiest fix involves repairing the
sealant boundary underneath the manufactured head of the weeping rivet. LocTite comes
to mind. Its success rate, however, appears to be mixed at best. If you are willing to pull
the tank, replacing that solid rivet with another solid rivet makes sense. If you'd rather
not pull the tank just to fix one single weeping rivet, replacing its solid rivet with a blind
fastener is an option. There is a lot of anecdotal evidence out there suggesting that
replacing a random weeping rivet with a blind Cherry rivet works well enough.
Faced with your situation, I would try your technique of using a syringe to try to squirt a
bit of proseal into the faying surface before replacing the rivet. Seems like a perfectly
reasonable idea and it can't hurt a darn thing even though it may or may not work. But
after I did that syringe thing and prior to reinserting a new rivet into the hole, I would
make especially sure that the replacement rivet and the countersink is liberally coated
in fresh wet sealer.
If only that single point of failure (
3) remains intact because of your repair efforts, that
rivet location will no longer weep because you have effectively interrupted the leak path
that continues to originate from inside the fuel tank.
This appeared at about 30 hours and I now have 90 on it. Never drips, just weeps while flying. Vans says to cut out the back baffle and reseal the interior flanges with proseal.... then reseal with a plate, proseal, and sealed pop rivets. Before I do that, I think I am going to try to just drill it out, proseal the heck out of it, then use a selfsealing rivet. If that doesn't work, I'll cut it open and rivet again and completely reseal that bay.
