Topic: Flaking paint on top of the gas tank?

[kyle750]

This is a big concern on my bike and I would greatly appreciate other members thoughts and opinions.  When I bought the bike I was expecting the worst of all worlds but there was some good and some bad.  The best good was that the engine was running well.  The worst bad was the extent of the rust throughout the bike and the flaking paint on top of the tank.  Looks terrible.

I believe the best thing would be to strip, sand, and repaint the entire tank NOW but as I am involved with so many other parts in the restoration I was hoping to leave the painting until near the end of the project (not the beginning).

I am very concerned with the cracking paint as you can see that rust is building in the exposed metal of the tank under the paint. It looks like the rust has been building for a very long time.    Would it be a good idea to deal with this now rather than later.    I can easily strip and scrape the flaking paint off and sand the rust on the metal underneath and paint with a metal primer just to prevent more rusting until I can get the entire tank properly painted later on.

Late Edit:  The photos were taken much earlier when the bike first arrived.  Since these photos were taken I have removed the gas tank cap and broken latch, filled the tank full (to prevent rust to the inside of the tank), used a fuel stabilizer in the gas, and added a temporary top lid (which is not working very well) 

[kyle750]

The reason I am revisiting this now is because the rainy season has just started here in Thailand.    After many months of dry and cooler weather we had a tremendous thunderstorm yesterday.  Anyone who has visited Thailand knows how furious the downpours are.    Today after the thunderstorm there is a thick blanket of humidity everywhere and I am sure the humid air is working its way into the cracks on the paint and the surface metal underneath 

[kyle750]

A quick gripe - the Honda CB750 gas cap and latch design SUCKS!

[rocket johnny]

the gas cap & latch on my 76 cb750 k-6 works great ,  easy to use and seals well .   yours looks a bit off kilter ,,,,

[kyle750]

  yours looks a bit off kilter ,,,,

off kilter is very kind . . . when the bike arrived the gas cap was tied down with a rubber band . . .   

[MauiK3]

I’d say remove the flaky paint and seal it up.

[kyle750]

I’d say remove the flaky paint and seal it up.

I agree that the flaky paint should be removed.  I'm afraid to see what is underneath and the condition of the metal?

[kyle750]

Here is the removed gas tank cap.  Rubber seal crumbled to dust and debris when removed.

[Ozzybud]

There is a safety recall on the push latch and Honda (in the past) would replace it with a locking device for free,, They are suppose to honor safety recalls forever.  At least in the states.
Apparently in a forward crash your kibbles and bits would slide  across the latch and open the tank upon impact. Not a good visual.

[kyle750]

^ ^ ^ Ouch ^ ^ ^

[M 750K6]

If you can afford it, while you're not riding, it is a good time to give it to a paint shop to renovate. It might be worth getting the inside corrosion treated then pressure tested, before paintwork.

Personally, if there is rust inside, I would get a good branded corrosion treatment on it, but not go on to apply a liner to the inside of the tank. It's very difficult to remove all traces of corrosion from inside the tank,especially the liitle creases and corners. A liner will separate from corrosion. Then you have a paperweight, unless you cut it open to remove the failed liner.

[kyle750]

If there are no objections I will try taking out the flaking paint tomorrow morning.  The paint has lifted from the metal and is very loose so it should be fairly easy to remove with a sharp knife.  If the top of the tank is badly rusted it is better to know now so I can start the search for a replacement tank. I will update tomorrow!

[kyle750]

I saw this CB750 gas tank for sale on Ebay and I just shook my head in disbelief.  Why would someone try to sell such worthless junk and even more baffling is why would someone want to buy it.  If the metal of my tank looks like this under the paint it will be tossed out.

[newday777]

You really need to inspect the inside of the tank with a bore scope before you decide to paint it. If the paint is peeling from leaks in the upper seam of the tank(the roof) from rust from the inside out, then painting now before finding out if the tank is viable and solid, will be a waste of time and money especially if you are farming out having it painted.
Here in the states we can go to an auto parts store and borrow a bore scope. (That's what I did before I ended up buying my own) you might check it out where you are or see if someone has one that you can take your tank to it have a good look inside before you get too far into it.(you will need to empty the tank 1st).

[kyle750]

You really need to inspect the inside of the tank with a bore scope before you decide to paint it. If the paint is peeling from leaks in the upper seam of the tank(the roof) from rust from the inside out, then painting now before finding out if the tank is viable and solid, will be a waste of time and money especially if you are farming out having it painted.
Here in the states we can go to an auto parts store and borrow a bore scope. (That's what I did before I ended up buying my own) you might check it out where you are or see if someone has one that you can take your tank to it have a good look inside before you get too far into it.(you will need to empty the tank 1st).

I completely agree 100% with everything you have said.  I should have inspected the inside of the tank with a borescope when I first bought the bike.  But I filled the tank with gas so I could start the bike and then later filled the tank to the very top so it would not rust.  Right now the top of the tank is a clearly visible known problem whereas the possibility of rust inside is still unknown?  If the top of the tank is rusted badly I have my answer and the tank needs to be replaced. I am sure this is going backwards and reverse but I almost always do everything in bizarre order.  Most people would repair the front brakes first and get the bike on the road but I just replaced the rusted steering stem bolt with a new chrome steering stem bolt.  No one cares about a steering stem bolt? 

[Ozzybud]

I saw this CB750 gas tank for sale on Ebay and I just shook my head in disbelief.  Why would someone try to sell such worthless junk and even more baffling is why would someone want to buy it.  If the metal of my tank looks like this under the paint it will be tossed out.

Outside surface rust is not a problem. The before picture is the rusty( on the outside)tank I bought on ebay.it looked as if someone stripped it and left it in the backyard for 20 years. Fortunately the inside was spotless.
Sanding most if it out and doing a conversion coating prior to epoxy primer took care of the rust.
I finished the new paint last week

[kyle750]

^ ^ ^ Very Impressive Work ^ ^ ^ The gas tank looks superb!  How did you get the inside of the tank so clean - looks spotless!

[kyle750]

I am very surprised.  If I find that the outside of the tank is rusted then all hope is not lost? 

[Ozzybud]

^ ^ ^ Very Impressive Work ^ ^ ^ The gas tank looks superb!  How did you get the inside of the tank so clean - looks spotless!

It was that clean when I bought it. Someone must have either stored it completely full or completely empty. Might have swished some oil around in there.not to sure but it was a great purchase.
Pic below is the original tank . Beautiful on the outside. Barnacles on the inside

[MauiK3]

There are various ways to clean the inside depending on the level of rust.
Some use vinegar.
There is electrolysis.
All require coating the bare, clean surfaces inside with a slosh of perhaps diesel fuel and maybe a mix of 2 stroke oil.
Many threads in the forum about this.

Some have coated the inside with tank lining products like POR15. I'm not very familiar with them.

[Ozzybud]

I am very surprised.  If I find that the outside of the tank is rusted then all hope is not lost?

It depends how deep the rust is.

[Ozzybud]

The above tank I cleaned with Evapo-Rust and it did an outstanding job less the couple of blisters in the paint where pinholes were coming through. I sealed it with Caswell epoxy and it sealed it up nicely.
I still opted to replace it with a better tank. Trick was matching the paint to the rest of the bike.
Pic after treating for 3 days with Evapo-Rust
As you can see it had some seriously deep pitting.

[kyle750]

CB750 Skin Surgery scheduled for this morning

What Lies Beneath?

[kyle750]

The flaking paint on the top of the tank is coming right off.  Easily removed with a knife.  I'm not exactly sure what is going on but it looks like the 1st layer is an acrylic filler (looks and feels like a hardened plastic) and the acrylic layer separated and lifted from the metal tank.

[Ozzybud]

This is what happens when you put body filler directly over the metal. It must have had some damage on the top of the tank that was fixed in the past.the proven method now is to use Epoxy Primer on the bare metal then bodywork on top of that.

How is the top of the tank?  Post a picture