Converting Vented Gas Cap to Non-Vented

[Gubi]

Figured I'd post a write-up of this since I did it. Moss sells a locking gas cap that fits the later TR7s, but since it's for British cars it is vented. It was pretty easy to pull it apart and convert it to the US non-vented version, though.

There's one small external snap ring on the central shaft holding it together. Insert the key into the lock, remove the snap ring, and then pull out the lock tumbler. Disassembly beyond this is pretty straightforwards: just remember where everything goes.

In the big round metal piece under the plastic cap, there are three holes with various ball valves and springs in them. The valve components are held in place by a flat plastic washer that's just pressed in place around the central shaft. I just pried off the washer and removed as many of the valve components as I could. Then I filled the three holes from both sides with adhesive (I used JB Weld) and let it dry.

See red boxes in pic for locations. Reassembly is the reverse of assembly.

[/url][url=http://www.flickr.com/photos/13048712@N07/5073713035/]

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Tom
'79 TR7
'87 Alfa 75
'91 Alfa Spider

[FI Spyder]

I've read you could do this for Spitfires as well, wasn't sure if there was a comparable solution for TR7 caps as well, not having a vented cap to play with.


TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

[andyf]

I`m showing my ignorance here, but is it necessary to convert to non vented?
I can see the logic in having to convert the other way round to prevent a vacuum occuring in the tank as it empties, but I cannot see why it would matter this way round?
Can someone more intelligent than me explain? [:)]


1980 Persian Aqua DHC

[Odd]

1 Out of respect for the environment?

2 To get the charcoal/carbon canister system to function as designed?

[bmcecosse]

My (UK car) petrol cap is not vented! Should it be ?

[Bobbieslandy]

Neither is mine, if i leave the car long enough the tank will pressurise. Strangely enough i can drive long enough to empty the tank in one go but i have no problems with vacuum. Must be a magic tank.

[FI Spyder]

UK system is different from N/A system. It (UK system) is like the systems of old (that where vented). When emissions came along with charcoal canisters etc. The systems where "sealed" to prevent gas fumes from venting into the atmosphere and producing smog that we've all seen hovering over LA and other cities not to mention acid rain. On a N/A system sealed system when you open the gas cap you will hear a whoose of air as it rushes into the gas tank to fill the small vacuum that is present. So if you have UK emissions on your car you need the vented gas cap so air can get into the gas tank as that is how it is designed to work and if you have the N/A emissons on your car you need the non-vented gas cap so there is a slight vacuum in the gas tank as that is how that system is designed to work. As an aside, a friend put a vented gas cap from UK on his car and he could smell gas fumes and when he got a non-vented gas cap for his car he couldn't because it was a N/A car. I don't know if you could smell the gas fumes on a UK emissions car (with a vented cap).


TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

[bmcecosse]

Well - there is no 'emissions' equipment on my engine - the cap is not vented - and there is a 'sucking' noise when I take the cap off ! Hasn't caused any fuel feed problems so far - but then I rarely drive more than 100 miles at a stint. -

[tencate]

1. Non-vented caps are required in California to pass emissions.
2. Ethanol blended gasoline (e.g., E10) has a shelf life of 2 months in vented systems, 3 months in non-vented systems (read this somewhere on the net, take it with a grain of salt)
3. What Odd said too

[Spectatohead]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tencate</i>

1. Non-vented caps are required in California to pass emissions.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
They're required here in Washington too. My Ford F-150 failed it's test this year because one of the two gas caps didn't hold pressure. I shelled out $8 for a new one and took the receipt back to the testing station and they signed off on it. Of course, if the vehicle is over 25 years old it is exempt, so the TR8 doesn't have to go through that indignity.

Jim Clark
'80 TR8
'97 Maxima 5spd

[Gubi]

Yes, as was explained the purpose here is to make the US emissions system work properly. From my understanding of the fuel system if you run a vented cap on a US car it effectively adds an air leak through the charcoal canisters.

Need a sealed cap to pass CA smog as well.

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Tom
'79 TR7
'87 Alfa 75
'91 Alfa Spider

[andyf]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Odd</i>

1 Out of respect for the environment?

2 To get the charcoal/carbon canister system to function as designed?
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Thanks Odd. I learned something new today.


1980 Persian Aqua DHC