How much rust in a gas tank is enough to need fixing? - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 11 Old 07-18-2012, 11:25 PM Thread Starter
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How much rust in a gas tank is enough to need fixing?

I bought a '77 BMW R75/7 that has rust in the tank. The owner has had it for 20 of it's 35 years, but only put about 8,000 of the 27,000 miles on it in that time. He always filled the tank with gas and Staybil, and drained the carbs when stored. It got ridden a few times a year when he was back from overseas.

Last year he rode almost a full tank of fuel out without a carb problem, and replaced the fuel and stored it for almost a year. During it's life, it has rusted anyway. Fired up and ran fine today. He said a BMW mechanic had looked the bike over for another guy last week, and he didn't seem concerned about the rust-- recommended the guy buy it. Seller seems like a stand up guy.

The rust isn't flaking and I see no sediment in the bottom. The interior looks like somebody simply took a can of rust colored primer and sprayed the inside. I can rub it with my finger, and nothing comes off. If I scrape it I can see bright metal underneath.

I figure if it runs without clogging the carbs, maybe it is something I should leave alone. I saw another one last week that looked similar, and it is being ridden, and the carbs had just been rebuilt by a experienced mechanic.

Tried to take some photos, but they made it look way worse than it is.

So.... leave it alone, shake it with gravel and sand (liquid sanding) or go the chemical treatment route and hope it doesn't eat up too much good metal?

Never tried this before. How about some pearls of wisdom?
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post #2 of 11 Old 07-19-2012, 05:00 AM
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I have a 1978 GS1000 that started rusting that way over 10 years ago. Myriad of rust spots but no where near rust thru.

I put an external fuel filter in the gas line. Changed it every couple years, but it has never clogged.

Ride it until it becomes an actual problem, or add an easily changed, clear filter would be my choice.

Austin

2002 DL1000 - 70K of joy, so far...
1978 GS1000 - One owner, still putt'n
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post #3 of 11 Old 07-19-2012, 06:05 AM Thread Starter
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Good idea. I used to do the same when I was into street rods, because the tanks I was forced to use years ago were of such an unknown quality (as in a freshly junked car). I had forgotten that option.

Thanks.
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post #4 of 11 Old 07-21-2012, 09:06 AM
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Quote:
Originally Posted by Austin44 View Post
I have a 1978 GS1000 that started rusting that way over 10 years ago. Myriad of rust spots but no where near rust thru.

I put an external fuel filter in the gas line. Changed it every couple years, but it has never clogged.

Ride it until it becomes an actual problem, or add an easily changed, clear filter would be my choice.
My wife's '94 has about a dozen 1/16-1/8" rust spots that I can see through the filler hole. It looks like surface rust, with no signs of flaking.

I took the factory Yamaha external filter off, junked the bracket, extended the lines slightly so you can replace it without removing the tank, and installed a cheap/common Fram inline filter.

I just consider it to be a couple dollar, yearly maintenance item.
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post #5 of 11 Old 07-21-2012, 12:35 PM Thread Starter
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Well, so far I have talked with a couple of guys who are more well informed (smarter) than me, and one said he seemed to recall these tanks came with a red paint or primer inside to prevent rust from the factory to the owner. My auto mechanic who owns bikes, said he didn't think there was much rust, if it was rust.

I did the old drain gas into a coffee filter and see what comes out trick, and I find a little bit if real fine black or dark brown grit. I've seen more on local girl's teeth than in the filter. I still need to take the tank off, give it a good sloshing around part full, and see what the coffee filter shows.

Then I will pull the petcocks and clean the screens, and make a decision as to just doing a paper inline filter, or roll some BBs around and do an inline, or try something like Evaporust.

I prefer cheap, simple and effective. I don't think I will need to line the tank.

Also, I jump started it and rode it to warm the oil. It idles, runs and shifts like a top. Some seeps from gaskets (like an old tractor) from over the years of sitting, and the plugs are black like too rich. Not oiled up though, which is good. All the lights and switches work, and somebody installed a world class horn-- no Roadrunner beep, beep....

Mechanically, I need a tach-- the needle is gone. Wonder if you can rebuild those? New tires, and battery, plus, filters and fluid changes. I will take the MAC 2 into 1 pipe off and go back to stock 2 pipes.

Cosmetics-- the battery side covers and tool tray are gone. Wish the little chrome grab rail around the seat wasn't gone. Otherwise she should be pretty slick when she cleans up-- very little rust on the frame and chrome.

So, she won't be showroom when I am done, but I won't mind being seen on her because she will look pretty good for 35 years, and 27,000 miles.....at least after I ditch the German fairing that came with her.
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post #6 of 11 Old 07-21-2012, 12:58 PM
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There's not much point in removing the rust if you don't recoat the tank. The original coating has failed, and it'll rust again. One local shop owner uses pennies and paint thinner in the tank with lots of shaking to clean out the loose rust and the chemical cleaner and coating to finish the job. With a good sized tank, you might need two bottles of the coating product to give an adequate coating. An inline filter would be the first step in any case.

Here's one good cleaning and coating product:
Gas Tank Sealer Kit For Cycles

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post #7 of 11 Old 07-21-2012, 02:49 PM
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I had my old 80's era GPz's leaky tank (at the rear tank mounting tab) repaired by a shop that could do some welding work to fortify and seal up my tank. It worked, so I figured I'd seal the tank to prevent any further rust from weakening the tank. Got one of those tank sealant kits from Kreem....you know, one bottle of nitric acid, and one bottle of sealant.

I masked off the tank paint as best I could, but getting all the nitric acid out of the tank proved to be a nightmare, with all the tank's anti-sloshing baffles and reserve chambers......I eventually succeeded, but lost the battle on the acid leaving some unusual paint damage marks at random areas where it defeated my masking efforts - oh well -but be advised!

The sealant worked - and the tank never leaked again.....but, if you do it yourself, factor in the possibility of having to repaint your gas tank.

"Side effects may include: Mild kidney explosions...Testicular cranberrying... And Rectal hallucinations."
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post #8 of 11 Old 07-21-2012, 09:53 PM Thread Starter
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Here is what I will be dealing with:



Looks like the mice had a good crop at least one year.

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post #9 of 11 Old 07-24-2012, 09:28 PM Thread Starter
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I finally decided it was time to get off the pot and make a decision. I am not going to do the BBs in the tank, and have elected to leave well enough alone. I buttoned the tank back up, and will add inline filters. I could see where the rust flakes came from-- the bottom left along the seam, and fortunately it does not look or feel like it ate much away. Flushes out about 3 pennies worth of metal.



Tanks looks pretty good (yellow streaks are reflections).... bike is a long way from looking the same.



Next up plugs, wires, filters, and fluids. Then brakes and fork seals. But not until this heat breaks.

Of course, when the heat breaks, I'll want to be riding the Wee, so this may have to sit until winter. It was in a barn for several years, so I guess it won't mind my garage.

Last edited by zzzzip; 07-24-2012 at 09:33 PM.
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post #10 of 11 Old 07-24-2012, 10:11 PM
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Is it leaking from the bottom seam yet?

"Side effects may include: Mild kidney explosions...Testicular cranberrying... And Rectal hallucinations."
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