twin tank venting

General Chat with an emphasis on BMC Minis & Other iconic cars of the 1960's. Includes information on MK1 Action days.
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Andrew1967
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Re: twin tank venting

Post by Andrew1967 »

I'm pretty sure I used a W shaped clip (one half either side) that are used to secure the two servo brake pipes together and fitted it using the screw (or stud) that holds the rear seat squab into place.

Will check on the car tomorrow.
Last edited by Andrew1967 on Sun Apr 07, 2019 9:31 am, edited 1 time in total.
Johnny
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Re: twin tank venting

Post by Johnny »

Factory right side clip on my August built 65 S. Upper left and right side clips are the same, held on with nut threaded to seat frame stud.
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AndyPen
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Re: twin tank venting

Post by AndyPen »

Thanks for the pics Swifty, I had totally forgotten that mine were originally like that.

I think I had those screw holes welded over - darn another mistake! Must check on my shell later.

Clips wise, didn't they use the same as the brake servo ones at the top?
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Nick W
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Re: twin tank venting

Post by Nick W »

Johnny...great image of your 65s vent pipes

Any one got images of post 66 factory set up with the welded on tabs?
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Johnny
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Re: twin tank venting

Post by Johnny »

Here are tabs from an unrestored November 66 build.

Image

A little mangled.
Image

These are from a March 67 car.

Image
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Nick W
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Re: twin tank venting

Post by Nick W »

perfect... thanks Johnny
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Peter Laidler
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Re: twin tank venting

Post by Peter Laidler »

Food for a bit of thought and nothing to loose sleep about and thinking out aloud as I'm prone to do, I was never convinced that these vent tubes in each tank served any purpose - except for one, below.
There doesn't seem to be any way that these vent tubes would prevent or even enable self syphoning. After all, the top of the vented filler cap is (at a guess) 1/2" below the highest point in the tank - where the vent pipe enters the tank. And of the car were left at a daft angle, with two (or even one) full-to-the-brim tanks*, the fuel would be pixxing out of the filler neck by then. And if you vent a syphoning operation, guess what happens?
They don't vent anything when the tank is being filled up, because the cap is off
They don't vent anything as the car is running, because the fuel filler cap is vented and allows sufficient air to enter the tank to replace the fuel
They don't cater for the expansion and contraction of the fuel or other atmospheric causes, because the fuel cap is vented sufficient to allow for this slow operation.
The only way these vents serve any useful purpose is when you are filling the, say, left hand tank (filler cap off....) which allows fuel to cross-feed into the right hand tank (cap ON). At this point, fuel is being fed into the r/h tank faster that the fuel cap venting can cater for - although it will eventually.

But that's my take on the real usefulness of them in a single tanked car. Maybe there's something in the construction and use regulations. Or are the vent pipes just a secondary valve in case the filler cap vent fails for some unknown reason? But they're there and we fit them!
(*don't forget that you can only fill the tank to the BOTTOM of the filler neck opening)
Twincam
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Re: twin tank venting

Post by Twincam »

I think many Mk1 saloons came with unvented caps and all the tubing is primarily for venting and tank balancing.
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Andrew1967
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Re: twin tank venting

Post by Andrew1967 »

Twincam wrote:I think many Mk1 saloons came with unvented caps and all the tubing is primarily for venting and tank balancing.
Estates and commercials would have vented caps and saloons are non-vented.

I wouldn't advise using a non-vented cap on a non saloon car unless you want petrol pissing out everywhere. Found this out on my pick up :oops:
gogsymac
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Re: twin tank venting

Post by gogsymac »

Johnny wrote:Factory right side clip on my August built 65 S. Upper left and right side clips are the same, held on with nut threaded to seat frame stud.
Johnny - are the vertical clips down the side of the right hand tank pop riveted in place or held in place with a self tapper screw?
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