[Paul B]

Really two tips:

1. If you use the "balloon method" of leak testing, don't assume you have no leaks if it appears the balloon is still holding air after several hours or even a couple of days. If you can't wait at least a week, you must apply soapy water over every possible leaky site and look for the bubbles. I had a known leak (small) and my balloon still looked the same size to me after 48 hours.

2. If you have small leaks around a few interior rib to skin rivets, at least try some of the alternate repair methods found on this site or others before cutting an access hole in the tank baffle plate. I used Permatex Green thread sealant and these steps to fix a leaky rivet on my newly constructed tank:

First, I sanded and then scotch-brited the rivet and immediate area so that it was very smooth, the idea being I wouldn't have to disturb the repaired area much when it came time to prep for paint.

Next, I blew it clean with my air gun, followed by a good cleaning with acetone, then hit it with air again and just to be sure there was no solvent left around the rivet, I let it sit for a few hours.

I then heated the area using hot air as recommended in the Permatex instructions for fasteners that are already in place. The tank was propped up so that the leaky area was as level as possible and I placed two drops on the rivet, wiping off the stuff that ran away from the repair site.

I let it sit for two days, then filled the tank with air and applied soapy water. No bubbles!! This might not work for every leaky rivet, but it's worth a shot!

 

[FredMagare]

Another tip: I repaired two small leaks in my rear baffle by thinning some mixed sealant with acetone and applying 1/2" of vaccuum to the tank to suck the slurry into the affected area. I found that a hand vaccuum pump took a long time, although it works to create a vaccuum. The fastest method was to attach the guage to the fuel pick-up with the appropriate fitting and a short length of aluminum tube sealed to the guage hose and use a shop vac at the drain fitting. Set everything up, turn-on the vaccuum, depress the drain fitting for about TWO SECONDS with the shop vac hose (do not make an airtight seal with vaccuum!), check the guage, and apply sealant (I used a shim of .016 to work it in). I know my tank withstood a half-inch of vaccuum but I'd be wary about trying for more....