A25 Fuel Tank Overhaul.

[DesertAlbin736]

Long awaited pics of my recently completed project to cut in inspection/cleanout ports in my 52 year old fuel tank.

I had been seeing some traces of diesel fuel ending up in my keel sump, apparently coming from somewhere around the tank. So I pulled the tank and pressure tested it with air & a spray bottle of Windex around the weld seams. Found a tiny pinhole leak around where the inlet fill pipe is welded to the tank, which I patched with JB Weld brand steel reinforced "Kwik Weld" epoxy. Of course to remove the tank & do that it meant completely emptying the tank which still had 14 gallons of fuel in the tank. I did so by using my siphon rig with the hose inserted into the hole where the fuel gauge goes & the jerry can on the ground next to the trailer, which in includes an inline fuel filter, to syphon fuel into 5 gallon jerry cans & use that fuel in my truck. Using a flashlight to look into the empty tank through the fuel gauge hole it looked like there was some crud accumulated in the bottom of the tank. So figured it was a good time to install cleanout ports.

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There was some discussion here earlier about ready made 'tank access plate systems" like this Seabuilt aluminum one from Fisheries Supply, for $328. But a) my tank is stainless steel, and b) I need two plates, one for either side of the baffle.

https://www.fisheriessupply.com/seabuil ... ate-system

Here was an idea from a blog for a DIY version, again in aluminum.

hatchplate_examplr.jpg

https://www.threefools.org/velocity/Pro ... sPlate.htm


Rather spend over $650 I decided to make my own in stainless steel access plate system. But, the fly in the ointment is that the tank is made from 18 gauge s/s sheet which is fairly thin & flexible and tends to "oil can", meaning not having a true, solid flat surface. And stainless steel plate that's thick and strong enough to maintain a flat mounting surface is a real beyotch to cut. I did find a local source here in Phoenix that had a break press they could use to cut 8 inch by 8 inch square 11 gauge plates, which is 0.120" thick, or 3mm, just shy of 1/8th inch. I bought six pieces for $134.48. The idea was to make inner and outer backing rings plus a top plate for each access hatch. I found an online source for 12" x 12" sheets of 1/8th" thick diesel proof Buna N rubber gasket sheets for $44.39 to seal the backing rings & the top plate. Another $88 for fasteners, that is #10-32 flat head machine screws & nuts to sandwich the rings together on 2" centers with the top ring countersunk for a flat surface, and 1/4-28 fine thread Allen head cap screws on 2" centers to attach the top plate with the inside ring tapped for those screws. I chamfered the corners 1.5" in from the corners. Total material cost for two hatches with gaskets & fasteners $266.87.

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Drilling accurate matching screw holes through the top plate & 2 backing rings was a challenge. I drew up a template on card stock paper to mark the holes then taped all three pieces together & used my drill press & C clamps to drill the holes & tapped the inner ring. It took a 4" pneumatic angle grinder to do the cutting, & stainless steel is much tougher than mild steel & certainly orders of magnitude harder than aluminum. Therefore much easier to cut square holes than round. Also since I don't have a heavy duty 240V air compressor it was slow going. I compensated somewhat but running an air hose from my small 2 gallon air compressor to an 11 gallon portable tank & from there to my air tool. With that I could cut for about 30 seconds and then wait for a couple minutes for the air compressor & 11 gallon tank to catch up.

Once I cut the access holes in the tank I could see what was inside. It had not been boiled out or cleaned in any way since well before we got the boat in 2014.

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Meanwhile, the bilge area under the where the tank goes was filthy. I thought of repainting it but in the end just degreased & cleaned it up.

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Finally after weeks & weeks during which I had a lot of other things going on with limited amount of time to work on it, we're back in business. I did have to move the forward tie down stick a few inches to clear the hatch plate. I did find that the spot welds holding the mid tank baffle in place were sound.

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Finally, having tank out & completely empty afforded me the chance upon refilling it to determine exactly how many gallons is in the tank at various gauge levels and how much is in the tank when the guage reads "0", or empty. Spoiler alert, the total capacity is closer to 18 gallons than 20, the practical capacity down to a 4.8 gallon reserve is 13.2 gallons, and +/- 170 NM range at 6.5 kts & 0.5 gph. So I posted this spreadsheet on the dashboard so I'll know exactly how much fuel is in the tank, how much it takes to refill at each gauge reading, and approximate engine hour & NM range I have.

Fuel level spreadsheet.jpg

[jerridsc]

Here is a picture of my sending unit location.

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[jerridsc]

My sending unit is in the deep end. Why would they do it any other way?

[tribologist]

My sending unit is in the deep end. Why would they do it any other way?

Most sending units has an arm so it makes sense to have it there. The float is in the deep end. It can be mounted on the deep end too. Does not matter

[tribologist]

Nice work Steve. Im a bit concerned over jb weld .and long exposures to fuel but it might hold for a long time. Make sure the neck is free from touching the hull or something else that could stress it. I think it would have been easy to TIG weld or braze it with silver solder. The later can be done with a small propane burner but hopefully it stay sealed. Its hard sometimes to find welders willing to work on tanks. Just backfilling with argon would have been quite a few $ but it would be possible to stand it up and fill the starboard side with water to save on argon. Even if i was brazing it i would have argon filled since there is no chance to get flux on the back or then clean it afterward. .

[DesertAlbin736]

Im a bit concerned over jb weld .and long exposures to fuel but it might hold for a long time.

The leak was a tiny, tiny leak in the filler neck to tank weld joint. It was barely detectable & found by slightly pressurizing the tank with compressed air to about 1 PSI by taping over the filler neck opening with duct tape, shooting air into the tank vent opening & spraying all weld seams & fittings with Windex glass cleaner like you would trying to find a leak in a bike wheel inner tube. The rest of the weld seams on the ends, the seam along the length of the narrow edge, the spot welds where the baffle attaches, and the various fuel pickup, return line, vent, & fuel gauge were all fine.
The version of J-B Weld (there are several different ones) is their "KwikWeld (TM) quick setting steel reinforced epoxy which include "Marine" and "Metal" in list of applications.

J-B Weld KwikWeld.jpg

I would be more concerned if it were a situation where the tank was under constant pressure like a compressed air tank.

[tribologist]

Easy enough to strap a sorbie pad around it and check at it now and then. If it hold it holds(very possible). If it starts leaking its not a big deal to empty it and lift it out and weld it then. One have to love diesel powered boats!

[Burton]

Thanks for the post— this offers another possible solution for us. Our A25 had sat for years—we pulled and cleaned the tank and the center baffle was just sliding around. I did not want to spend all the $$ for the premade inspection port, and we still have the baffle sliding around. (It is too large to remove through the sending unit hole). I upgraded the vent weldment to 5/8” and silver brazed it on, adding an inline whistle in the vent and new vent outlet fitting. This really helps prevent overfilling. But even with such a small weldment, the thin sheet stainless tank was warping with just brazing heat. The upgrade of an inspection port will be upcoming at some point for Slow Motion, and as suggested above, I think doing the inspection flange with silver brazing might be possible with heavy clamping, but it might be a gamble with the warping of the thin sheet steel of the tank. (In my experience, one must have fairly tight fitting mating surfaces for silver brazing). It would be worth a try.

[SalishAire]

When we put the inspection port in our fuel tank we also found the baffle spot welds had broken and it was lying on the bottom of the tank. Our solution was to use small bolts with gasket material under the heads/washers to hold it in place along the same flange where the spot welds had been. This also gives us the opportunity to remove it and check the end of the tank not visible from the inspection port in the future if needed. We have not had leaks from the screws as they have very little fuel pressure against them being on the top of the tank.

[Burton]

When we put the inspection port in our fuel tank we also found the baffle spot welds had broken and it was lying on the bottom of the tank. Our solution was to use small bolts with gasket material under the heads/washers to hold it in place along the same flange where the spot welds had been. This also gives us the opportunity to remove it and check the end of the tank not visible from the inspection port in the future if needed. We have not had leaks from the screws as they have very little fuel pressure against them being on the top of the tank.

Does this mean the baffle spot welds were in the same place as some of the new inspection plate flange? If so, that is a great solution.

[SalishAire]

Does this mean the baffle spot welds were in the same place as some of the new inspection plate flange? If so, that is a great solution.

The baffle is off to the side of the inspection port but it does mean we didn't need to add to ports as others have suggested. Next time I get on the boat I will try to get a clarifying photo.

[SalishAire]

Photos of our fuel tank showing the location of the inspection port and the two screws that hold the baffle in place.