Fuel cap pressure valve pic required

[Melcoagain]

As part of an investigation to why fuel "dissapears" from the car i decided to check the fuel filler.

Having dissmantled it i found it has one valve to allow air in and no valve in the counterbored pocket next to it which leaves a hole about 3mm diameter for vapour to escape.

Logic tells me there should be a pressure relief valve there - probably a spring + ballbearing + plastic retainer. Can't seem to find any info on this.

I have now blocked the passage with a rawlplug and screw.

Any one got any info or a picture.

I included a picture of the main components for future reference. The 2nd part from the left has the valve in and the empty hole.

[keith w]

Hello,

I dismantled mine a few weeks ago for the opposite reason. Every time I removed the filler cap, and sometimes that was difficult, there would be a big hiss as the pressure equalised.

I've attached a picture of the relevant part. If you zoom in to the right hand of the two vent holes you might be able to make out a tiny silver ball in a press in plastic seating. There is a very fine spring in there, as you expected.

 

Hope this helps.

[Melcoagain]

Thanks Keith thats exactly what i wanted.

Bet you cant get those parts any more. Bit fidly but i will power up the 3D printer and see what i can create.

I can find a ball bearing, spring stifness will have to be a bit of a guess and depend on what pens i can mutilate.

 

[Melcoagain]

Taking a second look. In your picture the disc is upside down. You can see from mine that the rubber seal goes on the other side.

So the valve shown is the one i have. Is the other one the same?

The witness mark around your disc implies it has been fitted the way you have shown at least once. 

 

I have no idea what the big rubber disc/seal under the top does.

 

[keith w]

Thats probably why I still have the vacuum problem. I took two caps apart but may have got confused while putting the good one back together. There's a bit of exploded diagram in the parts book but nothing as detailed as these small parts. I'll go back to the second cap which is still on the bench and see if I can take some more photos for you. The spring is so small I doubt if I could measure the compression force required but I'll see what I can do.

 

[Melcoagain]

My picture has all the parts the correct way up as they get assembled.

From your picture it looks like the rubber seal is missing so the metal disc has been inverted so as to pres on the on the filler pipe. Since the valve is the wrong way round it wont let air in so you should get vacuume in the tank as you run the fuel pump. Any signs of fuel starvation at the engine?

 

[keith w]

No I don't think so but I am being gentle with it after a major rebuild.

 

Here is a another photo I found which might help.I'm assuming there should be another ball for the bottom set but this is how they came out. Note the different springs.

 

I'll take a look at the other cap I've found and post anything useful I might find.

 

[Melcoagain]

Thanks Keith.

So i am definately missing a valve. And as i suspected it has a stiffer spring than the air in valve.

Seems a bit poor that the  red plastic discs are just a friction grip in the counterbore.

I am assuming the ball sits on the black disc as its smaller than the spring. This disk has to be smaller than the bore to allow air flow around the perimeter.

The spring sits in the bottom of the bore and the cap is pressed in to hold it all in place.

Now to invent a replacement.