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Old 26-10-2008, 08:10   #1
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Cutting My Fiberglass Fuel Tank

I have a 1983 Hunter 34 with the stock 25g fiberglass triangle-shaped diesel tank. Best I can tell, it has never been removed or modified. The tank has never given me any trouble (5 seasons).

The tank has no sending unit and filling it is a pain (give the smallest guy a flashlight). I'm tired of this...

There isn't a cutout to install a sender, so I'll have to make a cut. I'm looking at a hole approximately 2" in diameter.

My biggest concern is that debris will fall back into the tank, requiring complete removal. The alternative to removal would be an oversized hole that I would West System back together. The advantage of a big hole is that I can thoroughly clean the tank. The disadvantage is the loss of structural integrity.

Anyone have any suggestions? Anyone done this before?


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Old 26-10-2008, 09:21   #2
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A hole saw and two or three shop vacs!

If I had to do this I would start the 2" hole saw with the pilot drill set very short, so the pilot drill doesn't break thru. Then shorten the pilot drill even more so the hole saw will break thru first, and drill and keep those shop vacs sucking. I would even stop drilling frequently to vac some more. The piece will probably be stuck in the hole saw, if not you can either fish it out of the tank or even leave it in there.

Change your fuel filter after a few hours if you are the worrying type, in case a little dust did get in there.

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Old 26-10-2008, 11:25   #3
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If you are going to get in there with a hole saw, you might as well make the hole big enough to use as a clean out. But first try to see if and where any internal baffles are that could interfere with the float arm.

If the glass isn't thick enough to hold a self-tapping screw, cut a backing plate out of a piece of starboard and attach it inside with [dare I say it?] 5200. Mount the fuel sender in the cover plate and attach the coverplate to the tank with a gasket and screws. Don't forget that you need some clearance above the sender too.

Oh Yeah! EMPTY THE TANK FIRST, disconnect and plug the supply line, and clean every shred of glass debris out before you refill it
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Old 26-10-2008, 15:14   #4
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Well, I was hoping to avoid draining the tank (it takes most of a season under regular use conditions), so I like Oeansandmts idea. There's also an issue if I make a hole big enough for a cleanout - how do I cover it up!?
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Old 26-10-2008, 15:42   #5
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If you're going to the extent of cutting a 2" hole and have the room I'd cut an inspection/clean out as well. After five seasons I'd want to know what's on the bottom of the tank and have the ability to clean it out. Don't leave anything in the tank, this is one area to be anal about. Inspection/clean out ports can be had commercially or easily built yourself. It'll be well worth the time and effort.
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Old 26-10-2008, 18:54   #6
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I wonder if you could hook up compressed air to the vent line on the tank, so that once the drill bit passes through the fiberglass the dust and residue is blown out instead of falling in?

Don't know if blowing air across diesel under pressure atomizes the fuel... might be worth using a hand drill or pneumatic drill instead of an electric with exposed brushes.

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Old 27-10-2008, 14:48   #7
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Well, I'm sold on cutting a big enough hole for a cleanout. Now it's a question of what kind of access hatch to use.

Seabuilt stainless/aliminum inspection ports are the best, but expensive. If I can get away with a polypropylene or abs deck plate type fitting, I'd save more than $150...

Anyone have any recommendations? Any reason to avoid the plastic version for my fiberglass fuel tank?
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Old 07-02-2011, 13:25   #8
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seabuilt for the inspection port .. you will thank yourself for spending 100 bucks .. they totally seal with no leaks or smells and are made for this. for the sender make sure you know the exact hole size .. may be smaller than 2".

sometimes the things that may or may not be true are the things a man needs to believe in the most.
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fiberglass, fuel, fuel tank

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