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Now I have fuel in my tank and the fuel system is more or less leak proof I find that over a few days you get quite a pressure building in the tank. I guess part of the problem is that air can get (via the breather) but not out again. You can actually see the tank distorting with the pressure and you get quite a "blow" when you take the fuel cap off. I wondered if there should be a VERY small hole somewhere that lets the tank breath, perhaps in the filler cap. Has anyone else experienced this or have any suggestions?
Our tank does this as well, thought it was normal. Wouldn't a hole to the outside world mean that the petrol will slowly leak out as vapour?
I guess so - but you would only need the tiniest of holes and it would take a very long time to have any effect. Petrol tanks used to be vented like that in the old days - perhaps it's agin the rules now?
I’ve re-used the Ford Sierra tank breather system on my Cabrio which uses a small (ie approx 3 or 4 mm bore) diameter pipe to vent the tank to atmosphere. This system uses a small ball valve within the vent pipe that only shuts off if the car were to roll over (i.e. to prevent fuel leaking out) otherwise it’s continually open.
So I don’t think a small vent hole in the cap will give any fuel evaporation problems but could cause slight leaks during cornering (with a full tank) or when upside down (perish the thought!). I would avoid drilling any vent holes though until after the SVA…
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See my section at building 4 at my site
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Fuell neck.
I guess I have the cheapest new fuel cap ( from a motorsport boat) but the flexible line to the tank is expensive. I now have to prepare a T piece to get the air out while filling fuel at tank station. This also will be done by [url]www.catchtank.eu[/url] I studied the ford-filler-neck-assembly carefully. It’s perfect engineering with overflow, changing up-side-down airflow after a carcrash, air inlet while driving and air-outlet at taking in fuel.
My solution: A small pipe with flange to reduce diameter to satisfy SVA to only be able to get the unleaded fuel neck in at a gasstation. In the 51 mm fuel resistant tube is a connection to the 16mm tube at top. This tube blows air out at taking fuel quickly. The fuel cap has a seal in it and therefore is air closed. So when driving I have to let the air in, and if heated up the air has to get out as well. All of this of course with the cap closed. Imagine me at a circuit before a Tarzan corner with my hand on the cap to unscrew and screw immediately after it to give the tank air to prevent collapsing while driving. So bought the necessary air valve. Perfect engineering. There are two balls in it! In normal position -> air can get out only if the light green ball will be blown up. So no smell of fuel if my car is in the garage, resting after a hard day of work at a circuit. Only overpressure will go out. In this upright position no problem to blow through it to get air in the tank. The line milled out vertical in the thread is for this function. This will happen while driving and consuming fuel. 24 valves in the engine will use some fuel to work. If upside down (I assume due to an accident), the steel ball falls down and closes the complete airflow. Hope this position will never be used after position it.