What's this then?

[Bandage]

Sorry for the ignorance, but I'm a newbie minor owner ('67, 4 Door) and looking for some knowledge.

Elsie has had a number of modernisations over the years and so differs from the standard diagrams in the workshop manuals etc (front disks, electric starter, altanator). Compounded with me being completely new to vehicle mechanics, it's not a great combination for understanding what's what!

There's a fuel hose coming from between the carb and the cylinder head. It's not the fuel pump as it's running a normal SU type. No idea what it is, could someone put me out of my misery?

[Chief]

I think it's just an inline petrol filter assembly (presuming you don't mean the crinkly pipe from the air filter assembly that is?).

[Peted7202]

I think he means the copper pipe from the carb to the opposite side of the cylinder head.

[ManyMinors]

The pipe mentioned above is a replacement for the vacuum pipe isn't it?

[Bandage]

Sorry, not clear enough with my description!

I know the copper pipe is the vauccm feed for the distrubutor and clocked that it was an inline fuel filter.

Ive zoomed in on the picture below, fuel line with text on goes down to a 7" diameter cylinder in the bottom of the engine bay...

[Sleeper]

That's a servo for your brakes.... ( Vacuum pipe ).

John ;-)

[Bandage]

Ha!
So it's not got anything to do with fuel after all. That “suitable for unleaded" text on there had me perplexed!

Cheers chaps!

[geoberni]

Most cars in my experience, having a Servo, it's on the other side as less brake pipework needed.
But yes it's a Servo and remarkably it's the right way up.

[geoberni]

Ha!
So it's not got anything to do with fuel after all. That “suitable for unleaded" text on there had me perplexed!

Cheers chaps!

Well technically there is a chance of fuel vapour getting in the pipe, which is why installation instructions usually say a U trap should be in the pipework. Which you haven’t got.

Screenshot_20230422-132707_Firefox.jpg (58.79 KiB) Viewed 5495 times

I don't know why installers frequently omit a fuel trap bend which is described as important, while always fitting an additional one way valve when the instructions say that is advisable for 'high performance ' vehicles.

Screenshot_20230422-133455_Firefox.jpg (50.1 KiB) Viewed 5495 times

[Bandage]

Thanks for that, super Info. Where's it taken from?

Guess that's another job to add to the list

[JOWETTJAVELIN]

The fuel hose may collapse internally due to engine vacuum, it should not have been used for this job. You can buy brake servo hose by the metre so an easy job to replace with the correct stuff.

[geoberni]

Thanks for that, super Info. Where's it taken from?

Guess that's another job to add to the list

It's the standard instruction leaflet for the aftermarket Lockheed/AP Servo, widely available as a pdf file, this version came from Moss Motors:
https://mossmotors.com/media/instructions/981-173.pdf

A great many are fitted upside down, often by professional, classic car specialist garages. It doesn't help that the brackets can encourage incorrect fitting by their design.
In the video, the guy covers an incorrect servo installation: https://youtu.be/7-xPLRbDiDw?t=35

[geoberni]

JJ has a point about the type of hose used.
Vacuum hose is designed to withstand negative pressure on the inside, fuel hose is designed to withstand positive pressure on the inside.
That's really important on high performance cars, where the fuel line pressure and the vacuum pressure can be quite high.... I'm not so sure that applies so much to a paltry little A series engine of the 1950s.
Many Minor have a plastic vacuum line on the Dissy, so I can't imagine it's that high a value.

I've no idea what vacuum a standard A series engine will produce; I don't have a vacuum gauge.

Perhaps one of our knowledgeable engine guru's can help?

[philthehill]

It does not look as if the servo is mounted with the front higher than the main body of the servo as per the diagram above.
Having the front of the servo higher than the main body of the servo helps with bleeding the brake system

[svenedin]

Rather puzzling and unorthodox engine breathing system there too. Both a breather type rocker cover AND a tappet chest “chimney” type breather. The later engines with the tappet chest chimney usually go to an inlet manifold PCV valve and have a rocker cover without a breather pipe but a breather oil cap. This seems to be a hybrid system and not clear where the tappet chest breather pipe is going.

[Myrtles Man]

A great many are fitted upside down, often by professional, classic car specialist garages.

This video may shed a bit more light on why that happens:-

https://www.youtube.com/watch?v=seUiFtVX7uY

[geoberni]

This video may shed a bit more light on why that happens:-

So someone think it stops the fluid corroding the 'Air Valve'....
Umm, not convinced.
If you look at the explanation of how it works on the mgb-stuff website, you can see that if the seal perishes on the piston, brake fluid will get into the air valve no matter what way up it is.
http://www.mgb-stuff.org.uk/servo.htm

That video is, IMHO, a typical example of rumour spread by social media until it become a 'truth', simply because it's been shared so often....
It's how the Village Idiots are gaining the upper hand in the world; they share their lack of knowledge too much and with such conviction....

[oliver90owner]

That's really important on high performance cars, where the fuel line pressure and the vacuum pressure can be quite high

Not applicable to vacuum negative pressure. It cannot go above atmospheric (for most applications).

However, the inner sheath (in a normally pressurised system) may well be reinforced by the outer layers and will be if made of some materials (just think of clear garden hosepipe or garage air-line construction with plastic reinforced with other materials).

These inner layers may well be of insufficient mechanical strength to avoid collapse, when under negative pressure.

[geoberni]

That's really important on high performance cars, where the fuel line pressure and the vacuum pressure can be quite high

Not applicable to vacuum negative pressure. It cannot go above atmospheric (for most applications).

Perhaps I didn't word that well enough, I meant a higher gauge reading in both instances, which would be a lower pressure regards the vacuum.
A vacuum pressure can't be actually high, it wouldn't be a vacuum....

[Bandage]

Rather puzzling and unorthodox engine breathing system there too. Both a breather type rocker cover AND a tappet chest “chimney” type breather., [...] This seems to be a hybrid system and not clear where the tappet chest breather pipe is going.

Yes, when trying to work out what was what I've not come across a similar set up. Tappet hose is connected to nothing else and just vents down through the bottom of the engine bay.

If the chimney type is designed to have a breather oil cap, and I don't have one, is it doing anything?