Petrol cap

[imuir]

I have a banging noise coming from my petrol tank and when I remove the petrol cap I can see the tank expand,should my petrol cap have a small whole in it to allow air in as petrol is used, looks like to tank is under suction then expands when cap removed any ideas thanks

[shpub]

No. The venting is controlled via the purge tank and a roll over valve. Either could be blocked.

Bible has quite a section on these bits.

[tweety]

I was told by a main dealer to only do the cap up to the first notch, not tighten it right up, thus allowing breathing. I've also had a Chim that had a hole drilled through the centre of the cap.

Cheers, Al.

[ncs]

I do the same as Al, dont tighten it all the way. As recommended by the very nice man at Austec.

Nick

[shpub]

Bit of an urban myth this only doing it upto the first turn. Doesn't cost anything so worth a try but as the cap will stay tight anyway doesn't make much difference. Big discusssion on this in the bible including the thoughts of John Ravenscroft (we are not worthy...). Still worth a try.

The hole in the cap signifies that someone has solved the breathing problem the easy way and not bothered to sort out the blockage in the pipes and breather tank.

It does break the emission regulations as the tank is vented directly to the air but more importantly it would allow fuel to leak out in an accident. TVR fit a special roll over valve to the normal breather to prevent this. The hole just bypasses it. To be honest , not a clever solution.

[tvr4ever]

Had the same problem. Tried drilling a hole in the cap, at first it seemed to work. One drawback, everytime I started the car there was a strong petrol smell. So back to the undrilled cap. Then a local firm who makes some sort of a show lift for cars asked if they could use my Griffith for photos for their website. (www.sky-cat.nl) After the photoshoot there was some petrol leaking from a small pipe in front of the left front wheel. It turned out the car was at such an angle that petrol overflowed from the tank. After that I never had any problems with the tank making the banging noise. I can only guess that this petrol being spilled somehow cleaned the carbon canister and valve that are hidden somewhere in the car. Like I said, it's only a theory, maybe someone with a bit more Griffith knowhow (Steve Heath ??) can shed some light on this. For all I know maybe the solution is parking your car at a 45 degree angled car park (LOL).

Fred

[shpub]

That's the overflow pipe because I suspect you don't have the purge tank system as your car is a 4.x pre-cat car.

What can happen is that when the tank is filled, fuel gets into that pipe and can get trapped and it can come out when the car is tilted or when cornering. Tilting the car probably slopped fuel into the pipe and that is why it came out. Had the same problem on the 520 and had to fit a special breather valve on the breather/overflow pipe. Cost about £50. End of problem. with the cat cars this goes through the purge tank.

[tvr4ever]

Steve,

I wished my car was a pre-cat version. Unfortunatly I do have cats. I bought my car from a German dentist, so maybe they shipped the early cars with cat to Germany.

Fred