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TR4/4A late tr3 and tr4 gas caps


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What I am having trouble with is the gas cap for the later tr3 and I think that it is basically a tr4 gas cap. Does anybody know where it vents out?


Jedi Knight
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During the TR4 production run at CT19970 (according to Bill Piggott, Simon Clay in "The Original Triumph TR4/4A/5/6")the gas cap and filler neck were changed to a self venting cap. By incorporating the vent into the cap the need for a separate vent line from the tank was not needed. They also say the early and later self venting gas caps are interchangeable. I believe that you see if it is a self venting cap by looking for a small hole in the inner cap that is under the chromed out cap.

The TR3 and early TR4 had a fuel tank vent mounted on top of the tank on the right side of the car. It is a bolt on solid fuel line with a banjo fitting that the bolt passes through.


Great Pumpkin - R.I.P
FWIW, the cap on my TR3 (provenance uncertain) has the vent as well. I plugged the vent from the tank, as I discovered it was dumping fuel on the ground during hard left turns with a nearly full tank.

As Dave says, the vent is just a small (like 1/16") hole through the inner sealing plate. Trivial to add if your cap does not have one.


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Well thanks you guys I appreciate the response. I bought this car in the early 80’s as a basket case and I am not sure if the cap is original. It looks like the one that Moss sells with the rubber ring that fits late tr3. However, the cap has this little vent fitting that comes off and perhaps 1/8 opening at the end. It might be a tr4 cap I do not know. I did notice that a late tr3 cap and a tr4 cap from Moss use the same part number. I am just trying to find a place to vent this thing and I think that Randall is right it is really unnecessary. It is just one of those things I want to know. The tank also has the normal vent, so I guess, I might have a vehicle that has both, but again I am not sure. I will take some pictures. The part that makes me feel the cap could be wrong is that it takes some work to get it through the rubber ring and body hole with that little vent collar and then into the tank.


Great Pumpkin - R.I.P
sp53 said:
However, the cap has this little vent fitting that comes off and perhaps 1/8 opening at the end.
I don't believe that is a TR cap, then, unless perhaps someone has modified it. However there were other cars (including other Triumphs) that used a similar cap, and some of them might have had a vent as you describe.
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