oil tank cracks?

[BobJenkinsJr.]

well, we ran into a bit of a problem on the Cub with the C-85.
We have had a ongoing oil leak for the past several months
and suspected it was the sump gasket. Dropped the sump
and the replaced the gasket and ran the engine, still leaked.
After a 30 minute flight, leaked more! Running the engine above
1500 rpm, the oil really came out around the gasket, we thought.
Removed the tank and the area between the tank and flange
weld was leaking. It looks like the weld cracked and began leaking, getting
worse over time. The tank was new about 5 years ago with no
damage. We have 2 other old tanks and they both have been welded/
repaired in this area. My dad made up a plate to bolt to the tank flange
so we could pressurize the tank with air on the bench to find the leaks
with liquid soap. Welded the flange until no more leaks with air. Reinstalled
the tank on the plane and no more leak! After seeing the other two
tanks repaired in this same area, I guess this is common? Has anyone
else had/seen this problem? ???

 

[backcast]

 

[JimC]

 

[will767]

 

[JimC]

 

[bobbuilder1313]

 

[JimC]