Author Topic: What's inside your tank? (cb750) (Read 4853 times)

mystic_1 · « **on:** November 16, 2009, 06:23:39 PM »

This past weekend I cut up a stock CB750 tank in order to harvest the front mounts for a fiberglass tank that I have. If you've ever wondered what the inside of your tank looks like, here's some pics.

This is the donor tank. It was the worst tank out of my collection of four. Numerous dings and rust spots, plus a crushed rear right corner.

Used to be Candy Gold? Had the push-button latch so I think it was 72 or earlier.

I scribed a line around the perimeter where I intended to cut

and then went to town with a 4.5 inch cutoff wheel on an angle grinder. I made sure there were no flammible fumes present prior to cutting.

Some observations:

There are very distinct lines in the rust pattern that show where the fuel level was. As you can see the rust-free areas are in great shape and the rest of the tank would look like this inside if it was stored properly.

Note the rust on the bottom of the tank. This is caused by liquid water mixed in the gasoline. Water is heavier than gas so it sinks to the bottom of the tank, and causes rust over time. Due to a lack of free oxygen down there this process is not fast.

Note also the rust near the top of the tank, this is caused by water vapor in the air above the level of the fuel in the tank. You can clearly see that this tank was stored with about 1/3 tank of gas in it, and the bike was on the sidestand.

So, the lessons to take from this are, keep your gas tank as full as possible at all times, and drain it completely every now and then to remove any water that may have accumulated near the bottom.

BTW would anyone like the upper (outer) shell of this tank for any reason? I'll be using the tunnel, front and rear mounts, but have no use for the outside. Free to a good home, just pay shipping from area code 60007.

cheers
mystic_1

GammaFlat · « **Reply #1 on:** November 16, 2009, 08:12:31 PM »

I have always wanted to see the inside of a tank - and now my curiosity is satiated.

Thanks!

Johnie · « **Reply #2 on:** November 17, 2009, 04:36:41 AM »

Random thoughts here...so when you put Stabil in the tank for winter storage does that take the water out of the gas? What about the HEET product to remove water from gas tanks. Would that be good during winter storage?

andy750 · « **Reply #3 on:** November 17, 2009, 04:51:13 AM »

Very interesting! Thanks for documenting this.

cheers
Andy

mystic_1 · « **Reply #4 on:** November 17, 2009, 04:57:12 AM »

Stabil is a stabilizer that keeps the gas from breaking down. Don't think that'll do much to water.

HEET is a water remover, it'll work but I'd still drain the tank once a year or so (during spring cleaning).

Here's some relevant sites that discuss HEET for water removal.

http://www.goldeagle.com/brands/heet/faq.aspx

http://www.vw-resource.com/water_gas.html

mystic_1

Toxic · « **Reply #5 on:** November 17, 2009, 05:07:02 AM »

Very informative. You have skill with that cut off wheel.

JS550 · « **Reply #6 on:** November 17, 2009, 05:10:05 AM »

Is that a gold, wrinkle tank?

mystic_1 · « **Reply #7 on:** November 17, 2009, 05:11:18 AM »

Gold, not a wrinkle tank.

mystic_1

GammaFlat · « **Reply #8 on:** November 17, 2009, 05:34:24 AM »

Quote from: JS550 on November 17, 2009, 05:10:05 AM

Is that a gold, wrinkle tank?

At first glance, I was having a small heart attack (it's one of the right colors). A wrinkle tank has the "wrinkles" visible through the gas cap... so forward in the hump. They all seem to have some "wrinkles" near the back. Mystic_1 wouldn't be sawing up one of those. They're worth trying to save in that condition.

mystic_1 · « **Reply #9 on:** November 17, 2009, 05:40:54 AM »

Quote from: GammaFlat on November 17, 2009, 05:34:24 AM

Quote from: JS550 on November 17, 2009, 05:10:05 AM
Is that a gold, wrinkle tank?

At first glance, I was having a small heart attack (it's one of the right colors). A wrinkle tank has the "wrinkles" visible through the gas cap... so forward in the hump. They all seem to have some "wrinkles" near the back. Mystic_1 wouldn't be sawing up one of those. They're worth trying to save in that condition.

Yup, see pic below. If this were a winkle tank it'd be funding the remainder of my build

mystic_1

JS550 · « **Reply #10 on:** November 17, 2009, 05:51:23 AM »

aaaaaa...I see. I wasnt sure, saw the wrinkles there & thought that might be one.

JohnCurW · « **Reply #11 on:** November 17, 2009, 08:15:28 AM »

Someone educate a newbie, what exactly do the wrinkles infer? Some sort of rare tank off of a sandcast or something?

mystic_1 · « **Reply #12 on:** November 17, 2009, 08:23:43 AM »

Yup, sandcast tanks were apparently made with a different process than the production tanks, so they have more crinkles on the bottom.

mystic_1

ColinMc · « **Reply #13 on:** November 17, 2009, 09:01:13 AM »

Uh oh...so my 76 CB750 had a wrinkle tank when I got it then...a tank I did cut up and ended up throwing away since it was a failed attempt at making a custom tank...It wasn't in great shape...but I got another tank as a spare that didn't have the extra wrinkles in the bottom so I figured that one was better...

gar...

Don R · « **Reply #14 on:** November 17, 2009, 09:03:29 AM »

Some early diecasts also got wrinkles. Nothing wrinkled was made after early 70, I believe. Mine is an 11/69 build date.

ddrink · « **Reply #15 on:** November 17, 2009, 09:24:57 AM »

Quote from: mystic_1 on November 17, 2009, 04:57:12 AM

Stabil is a stabilizer that keeps the gas from breaking down. Don't think that'll do much to water.

HEET is a water remover, it'll work but I'd still drain the tank once a year or so (during spring cleaning).

Here's some relevant sites that discuss HEET for water removal.

http://www.goldeagle.com/brands/heet/faq.aspx

http://www.vw-resource.com/water_gas.html

mystic_1

Star Tron claims to do both

http://mystarbrite.com/startron/

lone*X · « **Reply #16 on:** November 17, 2009, 02:45:03 PM »

Mystic said: "HEET is a water remover, it'll work but I'd still drain the tank once a year or so (during spring cleaning)."

I do this every time a tank comes off for bike servicing, tune ups, and such, which generally has been a couple of times a year. But for those in cooler climates, wouldn't it be a better practice to drain the tank and refill it completely in the Fall before winter storage? Water free clean gas sitting in a tank for a few months has got to be better than gas with a years accumulation of moisture.

mystic_1 · « **Reply #17 on:** November 17, 2009, 04:02:22 PM »

My thinking is that the colder temps cause more condensation, especially during the spring thaw, and sitting for months on end gives lots of time for water to accumulate in the gas. Draining and refilling twice a year seems the safe route.

BTW it looks like Stabil Marine Formula contains a water dispersant that prevents water from pooling at the bottom of the tank.

mystic_1

BeSeeingYou · « **Reply #18 on:** November 17, 2009, 07:45:42 PM »

Quote from: Johnie on November 17, 2009, 04:36:41 AM

Random thoughts here...so when you put Stabil in the tank for winter storage does that take the water out of the gas? What about the HEET product to remove water from gas tanks. Would that be good during winter storage?

I remove my tanks, drain the gas and put it into the car. Then let the tank sit outside for a few days for the residue to evaporate. Coat the inside with sea foam and store it in the basement. With at best a 7 month season I don't care to run 6 month old gas, Stabil or not, in the spring. Condensation can be a real problem early and late in the winter and I have seen my bikes covered in it at times so I can only imagine what would be going on in the tank. It only takes a few minutes to take the tank off so why not. It has worked good and finally after 30 years I pulled the tank off my XS650 last fall for it's first cleaning and had only very minor corrosion.

754 · « **Reply #19 on:** November 17, 2009, 08:24:10 PM »

Maybe you should drain your username..

...

looks like rust is a big part of that.....................

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Author Topic: What's inside your tank? (cb750) (Read 4853 times)