PhilipB Posted February 2, 2022 Report Share Posted February 2, 2022 Willie's experience of a persistant fuel smell (TR4 section) prompted me to post the solution to my issue TR2 with replacement aluminium tank, vented fuel cap and vent pipe open to atmosphere. The fuel smell in the garage had persisted for some time and was at times strong enough to suggest a fuel leak. After checking fuel lines, taps and comnnections many times , I suspected the vent tube that comes from the top of the tank. With the car laid up for a while, I plugged the open end with a bung and waited. No further smell so I invested in one of these from Demon Tweeks and attached it to the end of the pipe. Problem solved and no more fuel smell in the garage Phil Quote Link to post Share on other sites
mikej Posted February 3, 2022 Report Share Posted February 3, 2022 Interesting device. A coincidence, but in the next TRA I have submitted an article on tank breathing - as part of a mission to keep water out. If you have a tank cap with a breather hole (as later TRs) then the original breather can be blocked off or removed and plugged. I can't think of one good reason not to! Mine was plugged 25 years ago on advice from another member with the same fuel smell issues. MikeJ Quote Link to post Share on other sites
PhilipB Posted February 3, 2022 Author Report Share Posted February 3, 2022 Mike I'm sure that would have been the cheaper and easier option but I have now fitted a locking insert into the filler cap pipe which seals off the vented cap. That retains the original look and provides fuel security but also counters any potential queries from curious scruntineers regarding the ease with which the standard fuel cap can be flipped open Phil Quote Link to post Share on other sites
Hamish Posted February 3, 2022 Report Share Posted February 3, 2022 I have a numpty question would the small breather hole in the cap cope with the vacuum that an electric fuel pump feeding a couple of webers whilst flat out ? the std breather pipe is quite a large bore for the job it does. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted February 3, 2022 Report Share Posted February 3, 2022 (edited) The issue with aluminium and other repro tanks is that they do not have the original internal cross venting pipe work. I have a replacement alloy tank and it stank the garage out when parked and the car when it was driven. This was until I put a blanking sleeve on the banjo bolt instead of the banjo and pipe assembly. My cap is original style for a TR, but has a small drilling in the sealing plate which provides the tank vent. No other vent was provided on the later car tanks and they have similar caps. My car has not suffer fuelling issues since deleting the vent pipe, and the stink is gone. 571086 was the factory supplied locking fuel cap. The example I have is self venting. It looks nothing like a flip open cap that we all recognise, it looks like a chrome mushroom with a key hole in the top. They are still available. For racing are you required to tape the fuel cap release mechanism in the locked position, so if the car gets inverted, or goes through the scenery, the cap release is not triggered too easily. The fuel tank filler locking device I have from a fellow forum user has a vent hole drilled in it. Edited February 3, 2022 by BlueTR3A-5EKT Quote Link to post Share on other sites
2long Posted February 3, 2022 Report Share Posted February 3, 2022 31 minutes ago, BlueTR3A-5EKT said: I have a replacement alloy tank and it stank the garage out when parked and the car when it was driven. This was until I put a blanking sleeve on the banjo bolt instead of the banjo and pipe assembly. Hi Peter: Can you explain this blanking sleeve to me? I did blank off my vent pipe (ally replacement tank) and am using the TR3 chromed flip-top top cap with the drilled vent hole. I too have some fuel smell and thought your blanking trick might help if I could figure it out. Dan Quote Link to post Share on other sites
BlueTR3A-5EKT Posted February 3, 2022 Report Share Posted February 3, 2022 (edited) 32 minutes ago, 2long said: Hi Peter: Can you explain this blanking sleeve to me? I did blank off my vent pipe (ally replacement tank) and am using the TR3 chromed flip-top top cap with the drilled vent hole. I too have some fuel smell and thought your blanking trick might help if I could figure it out. Dan Two ways of doing it. A simple screwed plug in the hole where the banjo bolt goes, with a fibre washer under the head to seal it. I think the thread is unf so probably available locally. or A metal tube, the same size internally as the banjo and same thickness. Basically a banjo without the outlet tube or outlet hole. Retain in tank as orig with banjo bolt and seal each end with a fibre washer. If you get stuck pm me and I’ll make you one but fear the postage might be stratospheric. Cheers Peter W Edited February 3, 2022 by BlueTR3A-5EKT Quote Link to post Share on other sites
TwinCamJohn Posted July 27, 2022 Report Share Posted July 27, 2022 Just visiting this topic for the first time. I have had a fierce smell of petrol in the garage which comes from the TR (TR3A). Whilst putting the car over a friend's pit it was clear there were no leaks anywhere and so the only open place was the breather pipe. I have the original locking cap. I would add that due to stupidity I drove off without the cap a few days ago and when I returned to the petrol station it wasn't there! That will teach me, they are quite expensive. I assume the "new" ones are made to the original specification. My question is, if the cap is vented, then can I block the breather pipe, or will I need to put on a pressure relief valve on the end? Quote Link to post Share on other sites
Lebro Posted July 27, 2022 Report Share Posted July 27, 2022 An original fuel filler would have a hinged cap, not one which could be removed ? But to answer the question, if the filler cap has a vent hole, then the original vent pipe can be blocked off. Bob Quote Link to post Share on other sites
TwinCamJohn Posted July 27, 2022 Report Share Posted July 27, 2022 Ah, I thought the locking cap was fitted on the later cars. So this is an accessory rather than original. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 27, 2022 Report Share Posted July 27, 2022 571086 was the factory listed option locking filler cap that looks like a chrome mushroom. It was offered as an accessory to a whole range of Standard Triumph cars. I think Wilmot Breedon made them originally. My one has a tag in the neck and a threaded stud and nut on the cap to allow a security chain to be fitted to prevent the problem you just encountered in the petrol station My cap is the same key as the ignition which ensures the cap has to be refitted before I drive off. http://www.leacyclassics.com/571086.html Quote Link to post Share on other sites
TwinCamJohn Posted July 27, 2022 Report Share Posted July 27, 2022 That's the one. Is it vented ? Not quite sure how to check. Quote Link to post Share on other sites
foster461 Posted July 28, 2022 Report Share Posted July 28, 2022 I blocked off that pipe in 2016 (due to the fuel smell) and never had any ill effects. The inner part of the fuel cap has a small hole in it. Is that pipe really a vent pipe or is is a fuel overflow pipe ? Quote Link to post Share on other sites
stuart Posted July 28, 2022 Report Share Posted July 28, 2022 1 hour ago, foster461 said: I blocked off that pipe in 2016 (due to the fuel smell) and never had any ill effects. The inner part of the fuel cap has a small hole in it. Is that pipe really a vent pipe or is is a fuel overflow pipe ? It is a vent as the original caps didnt have a bleed hole. Stuart. Quote Link to post Share on other sites
mike ellis Posted July 28, 2022 Report Share Posted July 28, 2022 As my cap has a bleed hole I fitted one of these to the end of the vent pipe. https://www.huddersfieldgas.co.uk/product/british-made-8mm-stop-end-brass-compression-fitting/ No smells and can now fill the tank as no fuel overflows on left hand bends Mike Quote Link to post Share on other sites
TwinCamJohn Posted July 29, 2022 Report Share Posted July 29, 2022 22 hours ago, foster461 said: I blocked off that pipe in 2016 (due to the fuel smell) and never had any ill effects. The inner part of the fuel cap has a small hole in it. Is that pipe really a vent pipe or is is a fuel overflow pipe ? So we are talking about the aftermarket locking cap? I had a look at mine (from Moss) and couldn't see a hole. Maybe I wasn't looking in the right place. Quote Link to post Share on other sites
foster461 Posted July 29, 2022 Report Share Posted July 29, 2022 4 hours ago, TwinCamJohn said: So we are talking about the aftermarket locking cap? I had a look at mine (from Moss) and couldn't see a hole. Maybe I wasn't looking in the right place. I have a regular TR3 fuel cap. There is the chrome outer cap and also an inner disk that seals against the rubber edge of the non moving bit. That inner disk has a 1/16th hole in it. Quote Link to post Share on other sites
TwinCamJohn Posted July 29, 2022 Report Share Posted July 29, 2022 OK Thanks. I have had a good look at the my cap and I think it will breathe. Anyway I have stopped up the breather pipe and the fuel smell in the workshop seems to have gone away. The TR isn't the only car but I think it was the guilty one. Quote Link to post Share on other sites
TwinCamJohn Posted July 23, 2023 Report Share Posted July 23, 2023 Just to revisit this thread. In my above post I mentioned that I have an aftermarket (Moss) locking petrol cap. I can't see any vent hole, but wouldn't the lock mechanism allow air through? Hope I am not being stupid! Quote Link to post Share on other sites
TwinCamJohn Posted July 24, 2023 Report Share Posted July 24, 2023 Bump. Quote Link to post Share on other sites
john.r.davies Posted July 24, 2023 Report Share Posted July 24, 2023 Breather, maybe. Another source is by percolation (?) through the hose wall. Teflon lined hose will cure, but it ain't cheap. John Quote Link to post Share on other sites
TwinCamJohn Posted July 25, 2023 Report Share Posted July 25, 2023 I just want to be sure that blocking off the tank breather pipe won't cause a problem. I did a temporary block and there didn't seem to be a problem. So I am looking for an opinion on the aftermarket locking petrol cap (Moss) which I have fitted. I would have thought the locking mechanism would allow some air through. The exit of the breather pipe is where the smell in the workshop is coming from. Quote Link to post Share on other sites
Ralph Whitaker Posted July 26, 2023 Report Share Posted July 26, 2023 23 hours ago, TwinCamJohn said: I just want to be sure that blocking off the tank breather pipe won't cause a problem. I did a temporary block and there didn't seem to be a problem. So I am looking for an opinion on the aftermarket locking petrol cap (Moss) which I have fitted. I would have thought the locking mechanism would allow some air through. The exit of the breather pipe is where the smell in the workshop is coming from. Those aftermarket locking fuel caps were designed to fit more than one vehicle and I would be amazed if it does not have a breather built in to it somewhere. Block off the tank breather and then park the car in the sun for a few hours. Then undo the cap and listen for a hiss of escaping pressure as you undo it. if there is no escaping pressure then the cap must have a breather. Ralph Quote Link to post Share on other sites
john.r.davies Posted July 26, 2023 Report Share Posted July 26, 2023 (edited) Maybe not ALL fuel caps. When I built Silverback, I had to relocate the fuel filler, and fitted an generic filler plate and cap. I had persistent tank vacuum problems, and tried drilling the smallest hole I could in the cap. And fuel will find a way! Fuel slosh drove a fine spray out on left hand bends! The best solution is a one way valve, so that air can get in, but the fuel cannot get out. John Edited July 26, 2023 by john.r.davies Quote Link to post Share on other sites
TwinCamJohn Posted July 26, 2023 Report Share Posted July 26, 2023 Ok, thanks, both. Quote Link to post Share on other sites
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