Lotus Elan

Fuel breather mods

PostPost by: vernon.taylor » Wed Aug 03, 2011 5:33 pm

Salut

I haven't read ALL the posts on this topic, so flame me if you must!

The primary requirement is to prevent a petrol smelling garage (and significant fuel loss). The other requirements must, of course, be satisfied as well - namely being able to fill the tank in a reasonable amount of time and allowing air into the tank to avoid fuel starvation. The other common claim of the Lotus system - fuel not spilling out when driving upside down - doesn't really apply to me as I have a cabriolet. I would discount it anyway in preference to the other advantages.

I spoke to Sean at Spyder about his system - one crossed over pipe leading to the filler neck, the other blocked off - and it does indeed rely on the filler cap not being airtight. I asked him what if it is and he said it isn't because there's a small hole in the cap and there is. I couldn't understand why he still takes the breather opposite the filler over the roof but I can't anyway. Logic (mine ;-) says why not just take the nearest breather tube to the filler neck? EDIT: with same bore tubing - what type? Gasket compound? And sender unit gasket to check.

Keeping in mind that all the filling stations in France are level (there's probably 'n' number of laws making sure they are) I ask you, Lotus lovers, why not?

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PostPost by: Jason1 » Wed Aug 03, 2011 6:58 pm

elan-plus-f13/fuel-vent-t14212.html?hilit=%20filler

No flaming from me, I don't think its helpful. Have a look at this posting I posted a pic of what Spyder used to sell.

I found that after I replaced the rubber seal (from SJSportscars ?3.50) the petrol stopped pouring out of the cap when I turned right. I also learnt not to put more than half a tank in. :D
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PostPost by: vernon.taylor » Thu Aug 04, 2011 5:58 am

Hello Jason

Thanks for the reply - I had seen the thread you mentioned, but there didn't seem to be a conclusion/concensus, if there is one.

To be methodical: Is the (very) small hole in the filler cap - on the underside, of course, inside the rubber seal area - a vent hole? To prevent vacuum in the tank is this small hole/vent enough? Would seem so to me even with an airtight rubber seal.

If the above is true, then venting for filling is all I need and the Spyder system seems to fit the bill - and why not (same question) just take the vent tube from the filler side directly to the filler neck?

I called Spyder and there is no problem to drill and thread the filler tube. From the photo they sent it appears that extra metal is added to make a flat - for better sealing with the brass tail - though looking closer at the grainy photo it may just be a washer. Anyone know?

Jason - did you drill and tap your neck yourself? What washer/jointing compound did you use to mount the brass tail? Did you find some pipe materials more porous than others?

Thanks and @+

Vernon
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PostPost by: john.p.clegg » Thu Aug 04, 2011 10:50 am

Vernon

As the petrol filler cap was sourced from the parts bin,I had one on my BSA,I think the pinhole is a vent/breather to allow air in, as the "motorbike" uses it, but on the larger fuel tanks we have on our cars,it is as useful as the chocolate fire-guard,hence Colin fitted bigger bore breathers,thrown over the rear window so as to prevent leaks as the car gracefully turns over...

P.S.

Spotted this

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :MESELX:IT

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PostPost by: Robbie693 » Thu Aug 04, 2011 12:03 pm

john.p.clegg wrote:Vernon

As the petrol filler cap was sourced from the parts bin,I had one on my BSA,I think the pinhole is a vent/breather to allow air in, as the "motorbike" uses it, but on the larger fuel tanks we have on our cars,it is as useful as the chocolate fire-guard...



Indeed - that's why I filled by hole with solder. No more leaks on right hand bends. I seem to recall reading that the cap was supposed to be non-vented, but I can't remember where or even if I imagined it!

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PostPost by: vernon.taylor » Thu Aug 04, 2011 2:23 pm

Salut les gars

Petrol filler cap - I inspected the hole and took off the metal and rubber disk. The hole doesn't seem to go anywhere - maybe one is supposed to drill through? As for leaking petrol on turns I would of thought that would be due to a bad rubber seal?

@+

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PostPost by: Robbie693 » Thu Aug 04, 2011 4:19 pm

Hi Vernon,

If I remember correctly there are two holes, one on the bottom side and the other, 180 deg opposed, on the top. The seal plate is hollow so it can vent from one side to the other. This effectively bypasses the seal (it would have to otherwise it wouldn't vent?)

All I can say for certain is mine leaked before and doesn't now :D

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PostPost by: Jason1 » Thu Aug 04, 2011 5:50 pm

Jason - did you drill and tap your neck yourself? What washer/jointing compound did you use to mount the brass tail? Did you find some pipe materials more porous than others?



No I did not get around to it, I found that replacing the flat rubber seal fixed the cornering leak.

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PostPost by: stugilmour » Fri Aug 05, 2011 3:07 pm

Vernon, assuming you have found a copy of the referenced Club Lotus article. If not, I have posted a copy below, along with a picture from the eBay listing John found.

The filler neck illustrated looks exactly like the part I used. Although I bought it on eBay (from a list member IIRC), I believe it is the Spyder part. The threaded bung is brazed or soldered to the neck (can't recall exactly), and provides about 4 or so threads to attach the screw in barbed nipple. The barb has to be removable to install the neck thru the hole in the body. The bulk of the bung is inside the filler neck for the same reason. Although I can't see it clearly in the eBay picture, I am assuming the nipple shown is threaded into the essentially flush bung that is brazed in place, see Jason's caution below. Note the orientation of the bung relative to the cap hinge is important to provide room to screw in the fittings; if making one up I would move it a bit toward the rear of the car to provide more clearance (say 15 to 20 degrees). The neck I bought was in about the same condition as the one on eBay; I changed the cap to new due to chrome pitting, which was an easy job. Buying one was great for me as I don't have welding/brazing skills. There was another lengthy thread within the last year detailing various fittings to make up the modified filler neck that might be helpful.

I modified the Club Lotus design a bit. I made up a 'manifold' of screwed fittings that I attached directly to the filler neck bung. This puts all the piping out of the way and above the top level of the tank, which is the important part for it to work. The piping configuration is identical, just the location of the junctions is moved. I had the headliner out when I made the mod, so installation of the over roof hoses was easy and I did not have to feed the reduced diameter hose thru the existing clear plastic stuff, which I can imagine to be the hardest part of the job. The stock clear tubing was in an awful condition in my car, all hardened and bent up. I would recommend feeding the small diameter hose thru the over-roof tubing first and considering a Plan B (headliner removal, corks in the hoses, etc.) if you can't install this tube, which is the 'secret' to the system working. As I didn't know how well the mod would work I installed two new full diameter hoses while the headliner was out, but I only used the small diameter hose placed inside a full diameter one as suggested in the Club Lotus article.

My replacement cap was bought from one of the major UK suppliers (Sue Miller or Spyder, can't recall) in the last few years, so I assume it is the currently available replacement that we are all using. It has the vent pin hole described above. It leaks on turns and if expansion from over-filling brings the fuel level too high. Thanks to all for the suggestions to correct this problem. :) I am going to try plugging the vent hole with some gas tank sealant I have to hand. I think the vent hole is where I am still getting minor vapour odour from, as any liquid spillage thru the hole leaks around the filler neck body gasket and gets soaked up by the soundproofing felts and takes forever to evaporate off. I don't have odors in the garage any more, but there is still a slight odour in the trunk that is gradually reducing.

The system works well, and has reduced the vapour problem considerably. I agree with the suggestion on the old thread about the vapour siphon causing very high evaporation rates on the stock system, which was much worse than on my BMW when it had a damaged vent hose open to atmosphere. Fuel filling speed is acceptable for the second half of the tank, although you have to slow down the filling rate a bit or fuel will slop out the filler. You can see vapour coming out of the neck bung, and can fill the tank right full. I have learned to keep the fuel about 1" down from the bung or it will be over-filled on a hot day with fuel expansion.

I think the modified venting system is fine in a roll-over condition because the single open over-roof vent pipe is always higher than the tank at some point within it's run, but I may be missing something. The only leakage I would expect during roll-over is from the cap, which should be minimal with the vent hole filled.

When considering this mod, recommend reviewing fuel integrity throughout the car. My fuel filler rubber elbow was rock hard; I got a replacement locally at an industrial supply. I also had a hairline crack in the fuel tank that was very difficult to see. Be careful removing and installing the tank if required; easy to put an extreme bending force on the fuel filler pipe damaging the weld; my replacement Ali tank from Axeminster addresses this issue with additional bracing in this area. Drain plug & fuel outlet on the tank, fuel gauge sender gasket, fuel line up the spine, fuel pump, and all hose fittings & hoses are other areas to check.
HTH
Attachments
Picture od vented filler from eBay.jpg and
Picture of the modified fuel neck with vent fitting.
+2 Petrol Tank Mod Club Lotus.pdf
Club Lotus article on the Plus 2 breather modification
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Last edited by stugilmour on Fri Aug 05, 2011 4:26 pm, edited 4 times in total.
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PostPost by: Jason1 » Fri Aug 05, 2011 3:37 pm

Just an after thought.

The new breather must only be screwed into the neck; if you braze it on then it makes it very difficult to replace the filler neck to car body rubber grommet.

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PostPost by: jeff jackson » Fri Aug 05, 2011 5:14 pm

At the risk of incurring everyone's anger, is there anything "modern" that we can replace the filler neck and cap with? I saw a Plus 2 once with a flush filler cap, and I'm pretty sure it had the flap inside to stop fuel slopping back out when cornering. Also this would be the narrow neck for the unleaded fuel filler hose.
Any thoughts?
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PostPost by: vernon.taylor » Fri Aug 05, 2011 7:29 pm

Salut Stu

Thanks for the lengthy reply. Yes, I have seen the Club Lotus article.

First off I have a cabriolet so roof tubes don't concern me.

Second my thinking is that the breather (not safety) function of the thin diameter tube in the lotus Club article is not really necessary if one of the breathers is vented into the filler tube as the filler cap has a vent itself - with heavy consumption at 70/80 mph about a litre of air would need to be 'sucked in' through the vent every 4 minutes or so. If fuel so easily slops out when cornering then I would think that 250ml of air could be sucked in in a minute. Linking the air above the main fuel level in the tank to the air above the fuel in the filler tube would also go some way to equalising the two air pressures - maybe helping the cornering problem (?). Hmm, no - both breather tubes would need to be vented into the filler tube - so that's more or less back to the Club Lotus article...

I found a suitable tail for a couple of euros - when I get back from holiday I'll ask a friend if he can solder/braze a boss fitting onto the filler tube. I'll then follow the Club Lotus article - more or less - not sure whether to seal of the vent holes in the filler cap and use a small bore venting tube or just rely on the venting of the filler cap, i.e. no small bore tube.

@+

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PostPost by: davidj » Tue Aug 09, 2011 11:39 am

Hi,

I still get petrol leaking out of the cap when the tank is over half full, despite doing the following!

1. New seal.
2. Replaced the inner rubber spring on the cap to get a bit more tension on the seal when the cap is closed.
3. My cap does not have the vent hole.

Any more suggestions anyone?

Cheers,

David
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PostPost by: alan.barker » Tue Aug 09, 2011 11:49 am

Hi david,
i think the only way is to machine an alloy plug with an "o" ring that slides inside the filler neck. o.k. each time you fill up, you open the normal cap, withdraw the alloy plug and put in the petrol.
I think somewhere on the forum there is a drawing of the alloy plug. One day i will get round to having one machined for myself
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PostPost by: john.p.clegg » Tue Aug 09, 2011 1:00 pm

David

One more thing,I lapped the top of the filler (emery on glass) to achieve a true flat ...

John :wink:
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