Black Thick Grime in Tank

mrtwowheel

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I just brought home a '81 Honda CB750C Custom, I already have two, this will be my third. Thought I'd take a shortcut and use this tank on my other CB750C since it has holes soldered and is waiting for filler and paint. There were no gas fumes in this tank. So, to clean the donor tank I filled it with three pounds of roofing nails and wrapped and taped towels around it, put it in the dryer, stuffed the dryer with old sleeping bags and comforters and gave it multiple no-heat spins while shifting it's position a few times. My plan was to use evaporust after this since I have 4 gallons stored away.. This process has worked very well for me in the past. So, after tumbling I took the tank outside to rinse it. Surprise, all that came out of the tank was clean water. Took a closer look and feel, what I thought was dirty rust was thick black crud, kind of soft and smeary. I never saw this stuff before. I bought a gallon of diesel fuel. Put a half gallon of diesel fuel in with the nails for scrubbers, closed off the bung and filler neck. shook it, let it sit, repeat.
The diesel fuel cut the crud but there is so much more crud still there. Wondering how many gallons of diesel fuel this will take. Any better cheap solvents I could use? Acetone would break the bank and gasoline might be an option since I'm not going to use a torch, probably no sparks either.

All of my other tanks have been clean, dry, but rusty.
 

Grimly

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I wonder if it's the same failed tank liner that Mailman had, which wrecked his top end, as it dissolved into the fuel and caked up the rings on combustion.
I'd try some samples of solvents in turn - gasoline, acetone, MBK.
 

mrtwowheel

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Grimly, I thought about tank liner too. No black grime in the see through fuel filter. No crud in the fuel hoses that i;ve removed. This stuff is thick. Don't want to use the fuel cap to seal it, fuel oil cuts right through my duct tape. There's a half gallon of diesel in there now. Gotta seal the filler neck somehow so I can let it sit upside down for a while.
 

mrtwowheel

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I've got it sitting on it's side without the diesel coming out. Gonna rotate it different ways like this with a little bit of diesel, then go get more diesel. If I start to see a good result I'll fill enough to reach the top of the tunnel. Thinking about toilet brushes.
 

mrtwowheel

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This stuff wasn't in the petcock either. I've been through the petcock, no obstructions, cleaned it and soldered on a new tube to replace the split copper tube. 1-7/8" long. I don't think I've ever had a whole tube on one of these Honda's to be able to measure it.
 
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Vincenthdfan

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Its congealed gas and new gas wont phase it in the least.

Acetone is my default for this congealed crap, it cuts through it immediately.

No need to fill it up for a soak, just a quart or two at a time shaken around will make quick work of it.

I've learned this through the school of hard knocks (read: experimenting with LOTS of other solvents/fuels that wouldnt touch it!).
 

mrtwowheel

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The diesel cut it pretty well. After two sloshings with the nails and a half gallon of diesel each I began to see specks of metal on the sides. I fished out the nails with a magnet. I put the petcock back on. My inner tube and zip-tie plug over the protruding bung had a slow leak. I can clean the petcock again, easy enough. After pouring in two gallons of diesel I saw bare metal and rust on the top of the tunnel, so I filled it to the brim with diesel. I'll let it sit like that till tomorrow night, then a sloshing or two with gas. Hopefully after drying it will be ready for the phosphoric acid. Unbelievable how much of this black stuff was in there, like thick uncured black paint.
 

mrtwowheel

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The tank is still sitting with diesel in it. It was a good chance to wire wheel the top of the filler neck. The paint on this tank is in OK shape and dentless. Forgot about this trick........plastic baggie over filler neck, locking gas cap over the baggie. I feel more comfortable now about using some acetone. Rubber wheel in the petcock leaks on OFF anyway, I can plug that. These petcocks are riveted together, but can be drilled out, all the way through, and replaced with small machine screws. Being riveted there is no rubber wheel offered for these. Ironically I half remember that the XS wheel is a fitting replacement, so I may ask to compare dia. and thickness.

You there Jim? How do you treat the filler neck top on the tanks that you paint?
 

ckahleer

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So, to clean the donor tank I filled it with three pounds of roofing nails and wrapped and taped towels around it, put it in the dryer, stuffed the dryer with old sleeping bags and comforters and gave it multiple no-heat spins while shifting it's position a few times.
Are you not married?
 

jetmechmarty

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Are you not married?
My wife is a feminist. If I slip, she corrects me that the washer & dryer are "ours", not "hers". So, I have put motorcycle fuel tanks in "our" dryer several times. I also use "our" oven for curing paint on occasion. I just wish she'd share in repair of appliances from time to time. I can't get her to change the oil on "our" lawn mower.
 

mrtwowheel

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My wife is a feminist. If I slip, she corrects me that the washer & dryer are "ours", not "hers". So, I have put motorcycle fuel tanks in "our" dryer several times. I also use "our" oven for curing paint on occasion. I just wish she'd share in repair of appliances from time to time. I can't get her to change the oil on "our" lawn mower.
I've put many enamel painted parts in my half of the oven. Especially when the weather turned and they were starting to blush. I own half of the dishwasher too, but that is nasty.
 

Jim

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You there Jim? How do you treat the filler neck top on the tanks that you paint?
Mostly I use a wire wheel on a drill to knock off the heavy paint and rust. Then I'll tape the openings up and throw it in the bead blaster. I just blast the areas the wire wheel won't reach.
 
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