The things you find..

[Don G]

What you have to do is clean the tank bottom, blast off the paint and rust etc. induce about 5PSI air pressure through a pet cock, don't over do it or the tunnel will bulge, as me how I know! Block the tunnel so it cant move, use a 4x4 or so piece of wood. Put a little water and dish soap mix on the whole bottom, have a cocktail and inspect for leaks.

[Chuck in Indiana]

Ewww, that's nasty looking, too..  did you manage to save it?

[Antietam Classic Cycle]

Just had another thought.. I've lined a couple of tanks with Caswell epoxy that turned out beautifully. That might be cost effective..

You'd still need to get the old liner out though. That's the "hard part", especially if you don't want to repaint the tank. I removed failed POR-15 with MEK (just a gallon, tank turned to a different position every hour... for days, the vapor actually does the job), followed up with 1 1/8" fine drywall screws with the tank tumbling in the dryer on "fluff". I made this special cap to make sure nothing got out and ruined the paint.

http://thisoldtractor.com/moto_guzzi_loopframe_gas_cap_replacement_-_sacrificial.html



It's in no way "sacrificial", being more durable than the tank it was attached to. 

[John A]

Find a different tank, hopefully in better shape. might as well cut your losses now. Its like you said, you don't want a career out of a  stinking tank, looks like you could have 40 hours in that repair and unless its the last one available, it might not be worth it.

[Chuck in Indiana]

Nice, Charlie.. 
I just talked to Mark at Moto Guzzi Classics, and he said, "Sure, I have some tanks. How good does he want?" Then, in typical Mark fashion, he tried to talk me out of buying one,  and putting Caswell epoxy in it. "It's the only one that works."
Basically said the same thing to me, as far as installing it. He said, "Why not gamble 50 bux or so on acetone and a Caswell kit instead of 3-500 on a different tank?" You have to love him.. what a character. 
We're going to SoCal in 3 weeks, so I could pick out which one the owner gets if the Caswell doesn't work.
Personally, I think the owner should get the nicest one he has and be done with it.. but I'll talk to him about that. Since he's paying labor, that Caswell job won't be cheap, either.

[Chuck in Indiana]

Find a different tank, hopefully in better shape. might as well cut your losses now. Its like you said, you don't want a career out of a  stinking tank, looks like you could have 40 hours in that repair and unless its the last one available, it might not be worth it.

Yeah, that's my thought, too, John..Shirley I wouldn't have 40 (billable) hours in it, but it would be more than it's worth.

[John A]

Yeah, that "billable hours" concept will bite you in the butt

[Don G]

Yeah I ended up saving that tank for now, it had a really nice original paint job, used 1 pound of silver bearing solder by time I was done, didn't record how many hours spent but it was a few.  DonG

[Chuck in Indiana]

Yeah I ended up saving that tank for now, it had a really nice original paint job, used 1 pound of silver bearing solder by time I was done, didn't record how many hours spent but it was a few.  DonG

Yeah, I get it. I can blissfully while away the hours on*my* stuff doing something like that. I can't when somebody is paying for my time. It just doesn't pencil out for them.