Ryan Stecken said:
Once again I ran into a special project.A friend is modifiyng a good olde CX 500 and wants to clean up his tank fuel cap.
He wants remove the huge stock filler cap and grind off the mountings and just run the turnable filler cap on top.
Problem here is the "indent" around the filler cap which he would like to fill up.
how would you guys go about?
I thought about grinding off and cleaning thouroughly than cutting up a piece of thicker steel and TIG welding it into place to make it sit flush with the tank top...
thanks!
Everyone has suggested a lot of good ways to approach this, but no one mentioned the finishing process... This is not mandatory, but necessary if you want professional results. Even if you don’t use this info, maybe someone will find it interesting.
After you cut out the existing section and weld in your new panel, regardless of method, the top of the tank is going to be distorted. To correct this you need to get a dolly similar to the contour of the tank and apply firm upward pressure below the weld while hammering with a low-crown hammer above. If you’re using a large modern-type filler cap you may get lucky and be able to squeeze your hand in there. Otherwise you’ll have to cut an access hole in the tunnel, which you can just weld up at the end. If you have any very tall weld sections you would carefully knock those down with a file first, otherwise leave the bead as is.
The planishing will do two things:
1. Flatten the weld to the point where no grinding will be needed. Remember, when you grind you remove material and sheet metal is already thin.
2. Compress and stretch the shrunken weld bead. This creates more surface area, and it has to go somewhere. The upward pressure you’re placing on the dolly combined with the momentum of the hammer strike will raise the newly stretched area correcting for the weld distortion.
You would be surprised how hard you may have to hammer on the bead, but be careful not to stretch too much or you’ll end up with a high spot. I prefer to get close with the hammer, and then switch to a slapper to fine tune it.
With practice you can create a filler-free repair. Although that usually isn’t practical. Using this method you can finish the panel to the point where you are satisfied.
I wish I had some better examples handy, but I've started deleting most pictures after the customer receives the work and gives the "ok". Here is a Honda tank that I recently did some work on. Along with making room for an electric fuel pump, the customer asked me to delete the side emblem mounts which are recessed similar to the fuel cap. These pictures show the weld distortion compared to the origional contour, and then after some hammer/slapper dolly work. I was already putting a lot of time into this tank for the fuel pump so the customer choose not to have me finish it all the way back to orgional contour, but close enough to be blended with minimal filler.
Hope this helps.