How much rust in a gas tank is too much rust?

[zzzzip]

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?

 

[FJRay]

I had a R90/6 that had a bit of rust like you are talking about. I put some small inline filters on it and never had a problem. I probably put 30k on it that way and the guy I sold it to is still riding it.

 

[wfooshee]

Well, we have someone who can tell you what rust does to FJR fuel pumps.

Dunno about gravity feed into carbs, though.......

 

[mcatrophy]

...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.

...

Stupid question, are you absolutely sure it's rust? I've often known some sort of brown residue in petrol tanks/carbs, I'm pretty sure it wasn't rust. We used to call it "tiger hair" after the Esso adverts doing the rounds then. Ok, I'm showing my age.

Test for rust? Not sure, but get some of the residue you've scraped off the tank, let it dry, add some propriety de-rusting compound, see if it turns grey (at least, that's what the de-rust stuff I have does to rust).

In any case, if it's not flaking and not building up in the float chambers, I'd forget about it. Trying to descale the tank may well cause more problems. Like rust

.

 

[zzzzip]

I had forgotten about the extra inline filters idea. I used to do that when I was into building street rods because I was forced to use gas tanks from the junk yard (I was a shoestring builder) and you couldn't tell what lurked in the corners even with the fuel pump access opened up.

There's been a bunch of Beemers going thru my area to a big rally in central MO this week. Lots of old airheads. Had lunch with 3 vintage airhead riders-- nice fellows. Maybe I should hang out at the truck stop and see if I can peek in a few tanks when they stop to fill up.

Looking on-line: Evaporust looks like it might have possibilities.

Thanks.

 

[XWinger]

If its a really light film of rust it shouldnt cause you any trouble.I bought a Nighthawk "S" new in 1984 & like an idiot stored it the first winter with the tank empty. The inside rusted slightly.I just sold it three years ago to buy my FJR & it still ran great with zero carb issues.

If you really want to fix it check out the POR-15 kit for lining a rusted tank.Did one over the winter on a 750 Katana that was really bad & it worked great.

 

[graler]

Cool finally a topic I can really chime in on. I have dealt with two rusty tanks in my past. One on a Nighthawk 450 the other a Nighthawk 700s.

The 450 I went the coating method. Chemical clean out and and coat. Moderate sucess with this. The hardest part is getting the tank really dry before you apply the sealing coat. I found this very stressful and was always wondering if I was going to get stranded on the side of the road from dislodged whatever. So peace of mind was non-existent and kept me from really taking off on the bike. That and that it was a 450 so it was a great around town deal.

I upgraded to a 700s (the bike I always wanted but my Mom guilted me into a no bike situation for decades). Found one and tore it apart cleaned carbs and such. It also had rust in the tank. I did some more research this time. I used the electrolysis method. Do a web search for Ken Frenchs Electrolysis method. It rocked and was kind of fun to watch the process. My troubles were only beginning though. After baking the tank all of the rust was gone but there was some other rubbery crap in there. A failed tank liner attempt had to use acid anyway. Got it all cleaned up and never coated that tank - just kept her full of gas. I also put an inline fuel filter on. Rode it for a couple of years then I saw an FJR. She was no longer the bike of my dreams - she now stood between me and the bike of my dreams.

The nighthawk in gone now but lives on as my avatar. The FJR is wonderful.

Joe

 

[RadioHowie]

"How much rust in a tank is too much rust?"

Oh...about THIS much...

 

[FJRay]

"How much rust in a tank is too much rust?"

Oh...about THIS much...

If you didn't live on the worlds biggest sand spit surrounded by salt water that wouldn't happen.

 

[zzzzip]

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 one of Smitty's Hooterville girlfriend'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.

 

[zzzzip]

Here is what I will be dealing with:

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

 

[gravity]

I agree stay with simple. It doesn't look like bad rust to me.

BB's can take off some if it but it doesn't look like you need to.

You could try white viniger (cheap bought by the gallon).

It's acidic and will take off the light rust.

A inline filter should take care of it.

I've got one that I'm toying with too

If you go for it, good luck with it.

 

[zzzzip]

After much sloshing and draining a full tank of gas, I pulled the petcock screens to find this:

And after dumping the remaining fuel, and sloshing some more around, this was about all the rust (at least the magnet says it is rust) I could come up with:

I figure that's not bad for 35 years. Looks like about 3 pennies worth of metal. With the interior of the tank dry, it looks like brown primer. I soaked the screens in white vinegar for a few hours, and the cleaned right up. So I think I will drop a tube of BBs in give it a shake, flush it with new gas, put the petcocks and screens back in, and install a couple of clear inline filters. If that fails, I'll take it to the next level.

 

[wheatonFJR]

Whadiddya do Skip? Pee in your gas tank or sumpin?

 

[someguy]

Here is what I will be dealing with:

that does not look like rust...

that looks more like the original tank liner with a lot of years on it...

the inline filter is the way to go. cheep and easy... and buys you time to better evaluate if there is even a problem here.

 

[zzzzip]

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. (Yellow streaks are reflections)

Tanks looks pretty good.... 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.