MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MG Y Type - Airtight Tank?


Dear all

I wonder if there are, or should be any means to allow air into the fuel tank to compensate for the volume of petrol that is used up when driving the car.

If no compensation takes place, could it be that a vacuum developes that pulls-in the walls of the tank - which in turn puts stress on the soft solder seams?

Attached please find two photos of the fuel filler cap that show no design features of an air intake....

Am I wrong there? I look forward to your replies

Anton & Swiss YT 4220





Anton Piller

Anton,

You are thinking like a 21st Century man! I doubt that anyone in the 1940/50's was concerned with VOC emmissions from automobile fuel tanks.

I would argue that the "seal" between the fiber disc and metal filler cap in your photos is porous enough to compensate for pressure differences from the fuel draw rate of the SU pump, as well as atmospheric changes from weather systems and diurnal temperature changes.

I have never noted indications of any vacuum/pressure conditions when releasing the fuel cap on any of my pre-1967 [i.e., pre US EPA Clean Air Act regulation] MG's.

Rocky
TC2482
YB0952
67 BGT
Rodney C "Rocky" von Dullen

Interesting that.
Just had a look at my cap which i believe is unmolested original, and it doesn't have a 'rubber' seal, just that centre dished washer and a brass cup similar to the large one under your rubber but deeper and up the other way and the edge of the cup seals (metal to metal) on the ledge of the filler neck
With the rubber setup you have there, when the cap shuts the rubber and large washer compress the spring and leave a gap between the smaller dished washer and the rubber, the air can then enter via the gap between the stud and the washers.

willy
William Revit

Hi Rocky & Willy

I'll try and check the setup of the CAP and innards with other Y-owners as soon as possible.

Rocky, I do not use a fiber disc - just a rubber one. Do you have a photo of your fuel cap set-up?

Willy, I have to check acording to your description. In the meantime, send me a photo of your Cap - if possible....

have nice weekend
Anton

Anton Piller

Anton
Couple of pics and my apologies, I mentioned the outside cup was brass but it's actually probably galvanized steel same as the centre washer- I doubt it's ever been apart as the car hasn't moved since 1959 and doesn't look like it'd come apart without drilling the centre rivet---which looks untouched
pic#1---open cap
pic#2---outer cup pushed in, it moves probably 6+mm




William Revit

Willy

Thank you for your two pictures. Attached please see a photo of our sons blue TD (for sample), and again the close-up of my Y fuel cap.

My Master Mechanic MG Teacher recons it would be advisable to let the tank "breath" a little bit.

The tank of my YT is not in situ at present, but it looks as if I can decrease the caps closing pressure by tightening up the the two counts-locked nuts inside the YT's cap.

Also, if the black rubber seal is to thick, I can go back to a cork seal....

I'll keep you posted
Anton





Anton Piller

Anton
Your cap looks very similar to your son's TD cap, both having a seal
---sorry about the dark pics but my car can't be convinced to venture outside---I'll get some light in there for a better try today.
Cheers
willy
William Revit

There's a few interesting pics here--TD-TF, the caps look a bit like what I have-----interesting

https://www.mgexp.com/forum/t-series-and-prewar-forum.46/gas-tank-vent-in-cap.3476435/
William Revit

Found some light - my cap looks similar to those in the mgexp link. Maybe it should have a cork ring in the filler neck --- don't know

willy




William Revit

All mine have cork William.
Paul Barrow


Willy

I agree with Paul - there should be a circular cork (I used thin rubber sheeting instead).

Luckily, my fuel cap uses two counter locked nuts, which enables me to alter the applied preasure of the cork, or in my case the rubber.
It will take some time and fiddling to achive the right "setting" to achieve a little bit of venting, without spilling petrol in every left hand corner...

Thank you all for your trouble
Anton
Anton Piller


Gentlemen

I found out the secret of the Tank Ventilation of Y-Types. It is the tiny hole in the special washer that holds the circular Cork / Rubber gasket (see attachment). A similar hole is found on the circular gasket - this clever set-up allows the tank to breath and ventilate through the cap.

Unfortunately the special washer in my YT's fuel cap is badly rusted and I will have to hunt for a usable one....

bye for now
Anton & YT 4220


Anton Piller

I concur with Anton's last picture.

My YT also has the "special washer" with a small hole in a pressed channel. But there's more...

If you undo the nut and remove the washer & rubber/cork, you'll find there's two small raised dimples on the metal plate behind that seal at 12 o'clock, on the same radius as the pressed channel in the washer.

The trick is to punch a very small hole in the rubber seal between those dimples at 12 0'clock, then replace the washer with it's hole at 6 o'clock. You now have a breather path via the channel, but the two holes separated by 180 degrees. This convoluted path prevents any sloshing petrol getting to the outside. Keeping the inside washer hole at 6 o'clock (lowest point) lets any trapped petrol drain back.

A nitrile rubber seal will give the best protection against petrol leakage under cornering, without dissolving. A vacuum lock will occur without the breather holes correctly set. Your tank won't implode but the engine will stall when the fuel pump can't overcome the vacuum.
R Ades

I was going to reply, but Robert said all I was going to say. I recall curing a slosh problem in Cecil's fuel cap about 33 years ago by fitting the missing cork seal. My dear departed friend Bill Spall ensured I included a vent hole in the seal.

Safety Fast

Tony Slattery
The Classic Workshop
(past owner of "Cecil" - YT3706)
A L SLATTERY

...Cecil's switch from a compressed cork gasket to nitrile rubber came after a few motorkhanas when the old material couldn't resist the excessive sloshing.

Discovery of vapour lock occurred next, then realisation of the original ventilation design.

Cheers,
Rob
(current owner of "Cecil" - YT3706)
R Ades

Thing is though, my cap doesn't look like that, the centre washer isn't held by nuts, it's a riveted setup and looks different ---I think the only way I can get a seal is to fit a cork/rubber ring onto the step around in the entrance to the filler neck-----?
William Revit

Hi Willy,

I'll defer to the real experts, but your fuel cap doesn't look like the original. I think the version that Anton, Tony and I have is correct for a YT. Yours looks like a later Morris/Nuffield design. Not sure how you can stick a seal to that metal disc in a petrol environment. Others may have a view.

Regards,
Rob
R Ades

Pretty sure it's original, I bought the car from a deceased estate and it'd been stashed away under a house since 1958/9 so only 10 years old at the time
William Revit

This topic is a bit old now, but in case there's interest...

Not the YT, but on our ZA Magnette we had a sloshing fuel problem. Strong smell of petrol in the cabin when turning right, a common comment from Magnette owners.

The fuel cap is attached to the filler flap via a plunger and spring, relying on the spring pressure to close the pipe. The plate to which the seal is affixed is a flat plate like Willy's, glued on, no retention nut and no obvious breather. It's as though the designers expected to cap to leak to avoid a vacuum lock.

The solution I'm experimenting with is a small snorkel set in a thicker gasket. This seems to be working.

The thicker gasket is a lamination of EPDM foam faced with a thin nitrile rubber sheet. I've cut open an empty aerosol can of degreaser and scavenged the solvent-proof plastic tube. Inserting a piece of tie-wire in the tube, I then bent a right angle whilst applying a heat gun. Once cooled, the wire was pulled out. This this bent tube was then inserted through the thicker gasket at the highest point, the outside end pointing up. I've used an oil tolerant gasket sealant as the lamination adhesive.

The result could be neater (this was my first attempt) but is hidden when the cap is closed and is working well. No spillage when cornering on a full tank. No vacuum lock. All the materials are standing up to the environment.

So I'm sharing here in case the knowledge is useful.


R Ades

This thread was discussed between 15/03/2024 and 26/04/2024

MG MG Y Type index

This thread is from the archives. Join the live MG MG Y Type BBS now