I set up our fiberglass tanks for front ports this weekend, and I learned some tricks.
Tools and Supplies
Here’s what I needed:
- all the usual fiberglass materials and tools
- A series of drill bits to step drill up to final size
- 37/64” drill bit for the finished hole
- ⅜” NPT tap
- ⅝” 12-point socket wrench
Thicker Walls
I added about ¼” of thickness to the areas where the new ports would be added.
I was surprised to find that the ‘glass work was so easy. My last experience with fiberglass was decades ago, and I remember it as a miserable, messy experience. This time it was easy. Smelly, but easy. After the first layer, I found it was best not to stay nearby while the resin kicked, because breathing the fumes left a funny taste in my mouth, even with the shop door open. Lots of fresh air is required.
After I had the thickness I wanted, I cleaned up the surface with a sanding disc on a die grinder. I recommend doing that outside; I used a dust mask so I didn’t breathe any particles in.
<Start Rant>
Realistically, this seems like a needless exercise. If the factory says we benefit from having a second port in the tank, why not just put the heavier wall thickness on the inside of ALL the tanks when they’re being built? They already thicken the tanks at the point where the rear port goes. It would be very little extra work and cost to thicken both locations. Then no one would need to do any fiberglass work. <End Rant>
Drilling
I looked up the right drill size for ⅜” NPT. It’s 37/64”. After a fruitless trip through Lowes, Home Depot and Harbor Freight, Ace Hardware had a two-flute HSS bit in stock ($20). I bought it because it was the only game in town. Based on my experience drilling other materials, I’d recommend using a four-flute bit, if you can find one. A two-flute bit in a hand drill is a challenge, and a four flute bit would make the drilling a far smoother operation.
I’d never drilled fiberglass before. I tried drilling a ⅛” hole and going in next with the 37/64” bit. That was a bad decision. The bit grabbed the ‘glass and ripped a chunk out of the tank wall; it wasn’t clear through, but it left more of a crater than I would have expected. Doh! After suggesting to myself that even idiots know about step-drilling in wood-like materials, I repaired the fiberglass with more resin and ‘glass cloth.
After it cured, I re-sanded the area and drilled again. The second time I went back in with ⅛” bit, and followed with ¼”, ⅜”, ½”, and 9/16” bits, and finished with the 37/64” bit. That way, the ‘glass drilled pretty easily. The final bit still wanted to grab, but I just moved in very slowly and stopped each time it tried to grab. I wound up with two nice holes positioned right opposite the existing ones.
Tapping
I figured a ⅜” NPT tap would be pretty easy to find. It was easier to find than the drill bit; Harbor Freight had one in a kit of ¼”, ⅜” and ½” taps and dies ($15), but it came without a tap handle. No sweat; I planned to use our tap handle. When I got home and opened the tap package, I found it has a full-size square shank, and our tap handle only takes up to ½” taps. Oops -- back to town, muttering about bad planning creating needless fire drills. That size tap handle wasn’t at Lowes, Home Depot or Ace, either. The Ace guy suggested a crescent wrench. I told him I’d considered that, but decided it wouldn’t provided much precision or control.
Then he suggested a socket, and it turns out that a 12-point ⅝” socket fits the tap just fine. I wasn’t sure if I had one at home, so I bought it ($3).
I got home and added a ratchet with a 3” extension. Bingo: a tool that works perfectly, provides very nice control, and is a whole lot cheaper than buying a giant tap handle just to tap two holes.
Before I started, I ran the tap down in an existing hole in one of the tanks and marked that depth on the tap; I took the new threads exactly that deep. [EDIT: Steve Dentz (
Stede52) notes that we should be sure we get the fitting all the way down so fuel doesn't contact the added material. I had to tap mine a bit deeper than they came from the factory.]
Tapping fiberglass is a lot like tapping wood -- move it clockwise ‘til it gets tough, and back up a little. Repeat, repeat, repeat . . .
So now we have two tanks with two ports each.
[EDIT: To get the fiberglass particles out, I blew compressed air in the rear port while the front port was pointed down. I shook the tanks pretty hard while the air was flowing, and it looks like I got all the little bits cleaned up.]
Here are pix of the original ports:
Fuel Tanks - Original Ports.jpg
. . . and the ones I added, with one of the strainers installed loosely:
Fuel Tanks - Added Ports.jpg
If you plan to add new ports to your tanks, I hope this helps . . .
You do not have the required permissions to view the files attached to this post.
