The CB1100 Community Forum

Hi everyone,

I recently bought a very well kept CB1100RS, but I noticed something unusual. There’s quite a lot of rust inside the fuel tank, especially around the top section and near what I believe is the breather hole/vent.

What I find strange is that the bike is absolutely pristine on the outside, yet the rust is concentrated only in this specific area.

My questions are:
How serious is this issue?
Is it something that can be repaired, or should I be thinking about replacing the tank altogether?

I’d really appreciate any advice or experiences you can share. Thanks in advance!

The inside of the tank looks clean, correct? Honestly, I wouldn't be too concerned on that amount of rust from what I am seeing in the picture if its just on the fill hole.

Looks like removal of that filler assembly would be pretty simple, though I don't have detailed drawings to look at. If simple, I'd pull it and deal with that rust before it becomes more of an issue. My $.02.

(08-18-2025, 08:19 AM)The A-man Wrote: [ -> ]Looks like removal of that filler assembly would be pretty simple, though I don't have detailed drawings to look at.  If simple, I'd pull it and deal with that rust before it becomes more of an issue.  My $.02.

Thank you for the idea, but only the "lid" is removeable, that rest is part of the tank, according to the Honda diagram:

That is a negligible, harmless amount of normal corrosion.  In a hot climate, it may be better to keep the tank fuller rather than emptier because condensation in the air within the tank makes it more rust prone.  The tank was manufactured and a rust coating/treatment was applied, and using wire brushes or rough pads can remove it.

If the rust was really bad, the tank can be emptied and removed, and the fuel pump taken out to allow a pretty large opening, and you can easily put your hand inside.  There is a large, replaceable, though pricey, mesh filter attached to the fuel pump, that likely can be cleaned or blown clear, so actual harm from rust is quite unlikely.

If it were my bike, I wouldn’t replace the tank. 
Good cleanup with ACF50 + cloth will be sufficient!

Agree with pekingduck and peterbaron, i would remove the allen bolts holding the filler assembly and remove it .
Then i would put something flat and good fitting over the holes in the bottom of the filler neck to stop any dust etc. contaminating the fuel.
Clean the dirt off the now exposed area around the filler neck with some cleaner solution.

Then clean lightly the loose rusty dust without removing the protective coating of the filler neck.
You could follow up with a small amount of "autosol" polishing compound to have a clean surface.

And smear a thin film of silicon grease ( or something similar which does not dissolve with fuel ) and repeat this over time to maintain a very light coating over the affected area.

also assemble the filler cap with some silicone grease on the mating surfaces and allen bolts threads to prevent more corrosion

It looks to me that condensation has build up under the fuel cap and worked its way down the affected area from being parked on the side-stand over time.

This tank should last the life of the motorcycle, nice pictures and welcome to the group, beware of salt spray on metal surfaces!

Max

Looking more closely at the pictures, the "corrosion" is all outside the tank, sitting in the well/trap area. This area captures rain and water and overfilled gas, and prevents it from flowing into the actual tank.

It has a drain hole that connects to a drain pipe underneath to the ground. Absolutely nothing to worry about. If you wanted to clean it out, you can take the cap off, plug the filler with a rag or rubber plug, and use an old toothbrush to to take the dirt loose, and vacuum or wipe it out.

On EX and RS models, only the rear 2 and front allen bolts are real - the other 2 are dummies and won't turn.

I agree with the technical assessment that other Forum Members have offered. I also know that like you I would like to see that portion of what is otherwise a perfect motorcycle also pristine.

I take detailing to a near obsessive level on my motorcycle. I am certain that with the right products and techniques, you can get everything where you want it to be. To add to to this already strong response, see my input for what it is worth:

For 2017 models and later, removing the gas tank is a little difficult. There is a bracket in place that clamps the fuel line that has to be depressed, not removed, to release the line. Because Honda does not sell the retention bracket by itself, I have avoided removing the tank for fear of breaking the bracket. Because you are working on something on the “top” of the tank, I believe you can clean the area without stressing to reach the area that needs some loving care. Good lighting is a must-have while you work.

I would recommend placing a furniture blanket or something similar on the tank to protect it while you gently scrub and polish. It is easy to have something slip, and the last thing we want is to scratch that beautiful tank.

Accept the process will take time and iterations. I recommend foregoing wire brushes or sand paper regardless of grit. A soft brush and microfiber towels will work in time when coupled with determination and patience.

For what it is worth, I cleaned far worse on my motorcycle when I took it apart to get things right. It feels a little tedious when you start but as the grime gives way, you will be happy. I hope you will share some pictures so we can celebrate the progress with you. David

(08-18-2025, 12:38 PM)pekingduck Wrote: [ -> ]That is a negligible, harmless amount of normal corrosion.  In a hot climate, it may be better to keep the tank fuller rather than emptier because condensation in the air within the tank makes it more rust prone.  The tank was manufactured and a rust coating/treatment was applied, and using wire brushes or rough pads can remove it.

If the rust was really bad, the tank can be emptied and removed, and the fuel pump taken out to allow a pretty large opening, and you can easily put your hand inside.  There is a large, replaceable, though pricey, mesh filter attached to the fuel pump, that likely can be cleaned or blown clear, so actual harm from rust is quite unlikely.

Hi Pekingduck. Can the $380.00+ fuel filter be cleaned, and reused?

Thanks.