Topic: Can a little spring cause this much damage

[kyle750]

Truly a crying shame.  Hard to tell what happened here but I am quessing that at some point the gas cap latch broke and then someone tried a makeshift  fix. Or perhaps the spring itself cracked the paint.  Just speculation here but once the paint cracked  then moisture got under the crack to the exposed metal of the gas tank, the metal rusted, and the  paint continued to lift off, exposing more metal and more rust , and on and on and on. 

[bryanj]

Seen several broken springs but nor paint damage like that on an original tank

[newday777]

More likely, is the center seam that are in these tank tops rusted from the inside out, from low fuel level while the bike sat unused and the ethanol absorbed ambient moisture causing the inside of the tank to rust.

This K2 is a friend's, he had left it 10 years with 3/4 tank of gas from 2012. When I opened the cap and shined the flashlight in the rust was thick inside that I could see. I took it home and started electrolysis cleaning it, 2 days later, the center seams stated weeping rusty water staining the paint. Until that point the rust was cleaning out well in the lower section and I thought the tank was going to be fine.

Unfortunately......
It's time for you to find another tank.

[kyle750]

I never even thought about the top of the tank rusting.  I looked inside the tank when the gas level was low and there is absolutely no rust in the bottom or sides of the tank.

[newday777]

I never even thought about the top of the tank rusting.  I looked inside the tank when the gas level was low and there is absolutely no rust in the bottom or sides of the tank.

You need a bore scope camera to see it.

[newday777]

Go to Autozone and get a borescope from their tool loaner program.

[newday777]

You don’t need a borescope to see the underside of the tank. Just use a mechanics mirror positioned inside looking up and forward. Shine a light on the mirror and the reflection lights up the tank underside.

But, if there was no rust on the sides or bottom, I doubt there’s accumulated rust on the underside causing that issue.it looks more like the filler neck has some leakage around its base that has allowed fuel to seep onto the top beneath the paint. It could certainly also be from a dent that was in the top but repaired via PDR. Lots of possibilities…

Inspection will reveal it

[kyle750]

I absolutely have to look at the underside of the top of the tank and do a more thorough inspection but I have no access to a borescope.  Slightly off topic - I have a good friend who needs a hernia operation and the hospital has given him 2 prices.  One price for surgery only and another price that is double with the use of a mini camera (Surgical Endoscope) during the operation.

Trying to figure out how to put the bike up on the center stand nearly gave me a hernia

[newday777]

I absolutely have to look at the top of the tank and do a more thorough inspection but I have no access to a borescope.  Slightly off topic - I have a good friend who needs a hernia operation and the hospital has given him 2 prices.  One price for surgery only and another price that is double with the use of a mini camera (Surgical Endoscope) during the operation.

No Autozone around you??

The surgical endoscope process probably means less healing time.

[kyle750]

The surgical endoscope process probably means less healing time.

I think you are probably right and I will tell my friend

[kyle750]

I just noticed the paint is also cracking above the gas cap.  Also the gas cap pin is not correct and looks like a threaded bolt and nut? Should be a pin and C clip?

[bryanj]

Nope, a riveted pin

[Don R]

 The cap has been removed and replaced but the problem is that the gasket has a tear in it, that lets small amounts of gas to get out and under the paint. A painter told me to remove the paint on the tank neck near the gasket so gas can't get under it.
  I had a tank that had a pinhole where the PO had bondo'd the emblem recesses and then looked for the  bracket holes with a tiny drill. He thought more bondo would fix it.

[Mark1976]

   Looks to have been repainted, look close, there's quite a bit of build up near the neck and latch. Combine that with a small gas leak and the constant pushing down to close the cap and that's what'll happen, The top and under coat shrinks and ya get cracks and lifting.

[kyle750]

I definitely need to inspect the underside of the top of the tank.  Perhaps buy a Surgical Endoscope and I will perform the hernia surgery on my friend for free.  How hard can it be - cut open with an xacto knife, install some steel wire mesh (chicken wire will work fine)  and then a few stitches or just use a staple gun.  Then I can scope the Honda gas tank. 

Is there a possibility that the inside of the tank is OK and rust free and the paint cracking on the top is only surface rust?  I am still shocked that there is NO RUST visible inside the tank.  Knowing the high humidity here in Thailand, poorly fitting gas cap, and sitting idle for 9 years - I would think that there should be rust in the tank? I really don't know how the bike was stored??

[BenelliSEI]

“You don’t need a borescope to see the underside of the tank. Just use a mechanics mirror positioned inside looking up and forward. Shine a light on the mirror and the reflection lights up the tank underside“

Just do as Cal suggests. You don’t need any special equipment. What you have are just paint blisters. If the tank looks clean, it probably is. That plaint will flake off if you even touch it and then you will see what’s underneath. I’d knock off the loose stuff, cover with some paint that is a close match and get back on the road! .

[kyle750]

Yes the paint is ready to just fall off in big pieces like ice shelves breaking off in Antarctica

[Phoenix]

I leaned my bike over for a few days to replace gasketes on the covers.  Straightened the bike up and I had the same paint damage around the lid just not as bad.  I installed an new gasket in the gas cap.  Now I have a half inch ring of bare metal around a third of the opening.  I guess it adds to the patina and the history.

[PeWe]

I’d knock off the loose stuff, cover with some paint that is a close match and get back on the road! .

That can be a good start. There are 2k rattle cans to withstand fuel.
Or a paint shop in Thailand might do a new upper part.

Add a tank sticker afterwards to get  eyes away from ev small differences.

The go crazy alternative:
https://www.yamiya750.com/index.php?main_page=index&cPath=246_157_271_242

All small parts cost some too

[kyle750]

Once I can get a good look at the underside of the tank I will know how to proceed.  If rusted I will be looking for a new tank.  If OK then sand and repaint the old tank and buy a new gas cap. Not the highest priority at this time but I am still diagnosing problems.  It is very helpful to get a better understanding of all the work that will be needed. Thank You Gentlemen!

As a quick note and against the wisdom of many others I started the bike yesterday.  After charging the battery the bike started right up but struggles with low rpms and jumpy power for a few minutes so I constantly have to give it more gas from the throttle or it will stall out.  After a few minutes it starts to level off then power stabilizes and begins to gradually increase.  After about 5 minutes it idles very well - even rpm and not jumpy.  Very smooth and steady and even from the sound you can tell that the engine is happy and not sruggling. Really amazing for a 50 year old engine.   I ran it for around 30 minutes to heat up the engine and hopefully burn off and expel any moisture.

I now understand that running an engine for short intervals is not good (Thank You for the excellent explanation)  but at this point I am running the engine just to see and learn how it operates and make sure all the electrical components are functioning normally.

[newday777]

"The bike started right up but struggles with low rpms and jumpy power for a few mintues so I constantly have to give it more gas from the throttle or it will die out.  After a few minutes it starts to level off then power stabilizes and begins to gradually increase.  After about 5 minutes it idles very well - even rpm and not jumpy.  Very smooth and steady and even from the sound you can tell that the engine is happy and not sruggling. "

That is very typical of these bikes. The norm. Nothing wrong with it.

[kyle750]

That is very typical of these bikes. The norm. Nothing wrong with it.

Thank You Sir.  This makes me extremely happy as  I really was worried.   I am used to modern EFI with immediate and steady power. 4 carburetors scare me but the sound they make is truly a joy - you can hear them breathing air.   

[newday777]

My typical start from cold, full choke until it fires up, lower choke lever and feather the throttle to keep it running a minute, then slowly take off for a slow ride about 5 minutes, then you can open it up a little more until fully warmed up, then let it open up and breathe.

[M 750K6]

Sorry if it appears like "damned if I do, damned if i don't", I would not run these air cooled motors standing still for 30 minutes. I would be very concerned about overheating.

Personally, I would forget about the cosmetic stuff for now, deal with anything that's still preventing you from riding, then ride it and use the engine as designed. If all runs fine, then you can sort the cosmetics as you go from there. Avoid causing fresh damage. 👍

[PeWe]

You need a cooling fan after ca 5 minutes idling.
A std table fan work fine. I use it when synching the carbs