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Tank under pressure and leak on the tank itself


d0ne91

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I bought a rc79 on february, 2017.

I faced an issue after 3 years: High presssure in the tank, a big pop sound happened when I opened the lock. 

I solved a explanation in an archived topic on this forum https://www.vfrdiscussion.com/index.php?/forums/topic/86555-vfr800f-8th-gen-fuel-tank-vacuum-problems/&do=findComment&comment=1071983

 

Root cause: during service maintenance, mechanics did not put a hose right back in place and then it was pinched. An official Honda Japan document was published and it related my issue. 

 

Solution: since my vfr was not under guarantee anymore (ended in february 2020) Honda has rejected to take the repair in charge. 

I was about get it welded by someone I know but I found the topic mentioned above and I sent it to my Honda reseller because I bring my vfr to them since 3 years for every service maintenance. They welded it yesterday and I got it back today. 

 

It's unbelievable to pay for a maintenance which is not done correctly: we're talking about a hose and just putting it back in the right place (it took me 2min to understand and put it at the right place). 

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Me too, mine was done by the main Honda dealer who sold me the bike at the 16k very expensive service 

 

 

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2 hours ago, fink said:

Did you not notice the tank hissing when you went to refuel?

 

Is it not supposed to hiss at all? Mine does a bit if it's down to the warning indicator. I think my previous one did too.

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16 hours ago, fink said:

No it’s not supposed to be pressurised, hence the breather, 

Correct - Well maybe!

With an unblocked breather hose there should be almost no positive or negative pressure. However very slight vacuum would be normal as the Vacuum relief port needs to overcome the slight spring tension of the internal fuel cap poppet type valve.(see attached picture showing vacuum poppet valve removed from vacuum port)

 

Like the Vacuum relief port, you would have to assume that the Pressure relief port would also have some form of internal one way valve, as without it, there would be no need for two relief ports!

 

To overcome the Pressure relief valve it might require slight positive pressure. So depending on conditions, you may have a slight vacuum, OR slight pressure when opening the fuel cap. The emphasis being, Slight! 

I'm guessing, this might help explain the strange gurgling/fluttering sounds (Ignition Switch OFF) we've virtually all heard coming from the tank after riding, the positive pressure (a hot engine heating the tank) overcoming a one way valve and venting. 

 

ALL 8gen Owners need to be very aware of the potential for a blocked breather EVERY time the Fuel Tank is lowered from the Maintenance Position! AND, as the tank is lowered the breather hose needs to be pulled (at the small to big hose coupling on the R/H side) to take up any slack to prevent the smaller hose section kinking.

 

A blocked breather on these bikes can mean not being able to open the fuel cap, AND enough vacuum can build up to severely deform and damage the tank. Also, in hot conditions the opposite can occur, with a filler cap that almost explodes as you unlock it, as well as damaging outward tank pressure buildup!

 

Any noticeable strong buildup of Vacuum or Pressure, the next time you fill er up, needs to be taken seriously, and the breather hose checked.

 

Something workshops need to know and be aware of, but I guess, it's something they could easily forget!

 

Cheers :beer:

 

image.jpeg

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On 8/29/2020 at 4:57 PM, Grum said:
 

 

A blocked breather on these bikes can mean not being able to open the fuel cap, AND enough vacuum can build up to severely deform and damage the tank.

 

Like Grum said: Make sure the tank vent is clear and remains open or the fuel pump
will create enough vacuum to collapse the tank... I've witnessed a
Honda tank collapse because the dealer installed a California tank on
a 49 state bike and the cap wasn't vented like this Ducati example...

110025d1336135177-gas-tanks-noise-collap

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  • 2 weeks later...
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On 8/29/2020 at 7:57 PM, Grum said:

Any noticeable strong buildup of Vacuum or Pressure, the next time you fill er up, needs to be taken seriously, and the breather hose checked.

Can confirm.  I ignored this once on my 6th gen, and my tank quickly ended up looking like the Ducati busylittleshop posted.  I can't remember what hose/hole was blocked, but when the temps dropped, the tank shrank.  :()  

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The issue isn't restricted to 6th Gen.  My Gen5 had a kinked vent hose by the PO and he had collapsed the tank..... I was fortunate to find a NOS one.  I replaced all the vent hoses with stronger walled ones and lengthened and routed it such that it can't kink.  I suppose one could put some of that spiral wrap on it to accomplish the same thing.

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I have the same issue on my 2016 vfr. It was quite crazy for me in the beginning because my older 2010 vfr vtec doesn't have this issue. And I was thinking that is quite normal. But now it is fixed. Before, my pipe have narrow angle but now it is working great.

 

On my bike this pipe was on right side. 

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