How To Repair A Crack In The Plastic Gas Tank On Your Dirt Bike. Cracking your gas tank sucks twice; first, you get stranded, then you have to get a new tank. If you have a metal tank, no problem, hose it out and weld it back together. If you have a plastic tank, your options are limited. Long story short, JB weld PlasticWeld does not work. It was only $8, I was in a hurry, and I could get it locally, so I gave it a shot. I was suddenly no longer in a hurry for round two, so I had time to fix my tank correctly.