S3 under bonnet fuel hoses

[Will53jgr]

Hi All,
I want to replace the under bonnet fuel feed and fuel return hoses (part numbers C34912/1 and C29860/11) on my S3.

The problem I have is that I cannot get the fuel hose fully onto the metal pipe which crosses the engine and feeds both pairs of carbs. The inner diameter of the hose is 7.5mm and the outer diameter of the metal pipe is about 10mm. The fuel feed pipe from the pump to which the other end of the hose joins is smaller (outer diameter around 8mm) and so less of a problem.

I have tried lubricating the join and softening the hose in hot water, but can only get it about 10mm onto the pipe (the original was fully on at about 30mm. It seems that the hose will only stretch a limited amount close to the cut end, but not enough further in to push it fully on.

Any advice on how to proceed would be welcome.

I purchased the replacement hoses from one of the usuals (it is Cohline 2192 with stainless steel braided cover). Is there a better and more pliable hose for this under bonnet location or has anyone fitted a bigger internal diameter?

Many thanks,

Will

[DWW]

What is the outer diameter of that hose, if it is around 10mm you could sleeve it with a larger piece and two clamps.

[MarekH]

Make sure there are no nicks on the metal piping and use a very emery paper to make it smooth and friction free. Then try with Vaseline/petroleum jelly. The right size hose would have been an imperial measure originally.
kind regards
Marek

[Will53jgr]

Hi Danny,

The OD of the hose is about 13.5mm (without the stainless steel cover).

Thanks for the reply

Will

[Will53jgr]

Hi Marek,

Thanks for the reply

I tried your suggestion of emery paper to smooth the pipe and then vaseline, but still could not get the hose any further onto the pipe. As you say the original hose would have been imperial (5/16 inch and the 7.5mm sold as equivalent is slightly smaller). It seems possibly that it is asking too much of the 7.5mm hose I have to stretch sufficiently to slide 3cm onto a 10mm OD pipe. Have you replaced these hoses on your S3 and or could you recommend an alternative suitable replacement?

Many thanks

Will

[bitsobrits]

Any advice on how to proceed would be welcome.

Will

Buy bigger hose. If the pipe is actually 10mm (.394"), then you need a 10mm or 3/8" (.375") hose.

It's asking too much of a 7.5mm hose to get it to stretch to 10mm. I wouldn't even try with a 5/16" (.3125").

[Bob.]

Hi Will
The fuel supply pipe on the RHS of my car is 3/8" (9.5mm) O/D as is the engine crossover pipework. The return pipe on the LHS is 5/16" (7.9mm). Not sure if it's possible to do, but you haven't got the two sides mixed up by any chance? Otherwise it sounds as if someone has fitted un undersize supply pipe in which case you just might get fuel starvation when travelling continuously at above about 130mph.

[Will53jgr]

Hi Bob,

Thanks for the details of the feed and return pipe measurements. I have checked under my car and I do have the correct size feed pipe 3/8" and the smaller return. I think I must have mis-measured the feed pipe originally and did not notice because I was concentrating on trying to persuade the supplied 7.5mm feed hose to fit on the 3/8" crossover pipe (the suppliers are now sending the correct size). Not really an excuse, but an explanation and I am grateful for your post which led to my looking again.

Just to clarify, on the return side is the short piece of hose between the crossover pipe and the non return valve 3/8" ID or 5/16" on your car?

Will

[Bob.]

Hi Will,
Glad it helped.
Afraid I can't measure the stub pipe from the crossover pipework without taking the hose off, but judging by the OD of the hose the stub is 5/16" OD. The pressure sustaining valve it connects to has an arrow and the word "TANK" etched on it suggesting that both ends are the same size, otherwise there would be no need to mark it and it is a 5/16" bore hose connecting it to the steel return pipe so I think all the steel components of the return system are 5/16" OD.
Can't you measure yours?

[Will53jgr]

Hi Bob,

Yes of course when I get to replacing the return side hoses I will find out. Thanks once again for your posts.

Will

[Craig Balzer]

Wil said: "Yes of course when I get to replacing the return side hoses I will find out."

Will - I am restoring a Series III and have EVERYTHING in pieces.
I can easily measure most anything.
As I understand it, you are looking for the size of fuel line or the diameter of over-the-top-of-the-engine fuel lines and both ends of the non-return valve -- correct?

I'm heading out to my hobby shop within the hour and will post some number of you.
Do you prefer measurements in inches or mm?

EDIT
Will - I can provide dimensions of the non-return valve now; just recalled (while searching for my hard fuel lines) that they are in the post returning from being cad plated. Should have those dimension within ~4 days.

OD of long end and short in inches and mm's
The "long end" feeds toward the fuel tank and houses the spring and check ball

First measurement (in inches and mm's) is of the short end




Next two measurements (in inches and mm's) are of the long end




Finally - ID of the fuel line on the non-return valve.
Somehow managed not to capture the ID in mm - both ends are the same (5.02 mm)


Bonus Photo - exploded view of he non-return valve (pretty simply thing, really)

[Will53jgr]

Hi Craig,

That's great information on the non return valve thank you. I have the outside diameter of the engine crossover fuel line and also the feed and return hard lines so your photos have completed the picture. Again many thanks for taking the trouble.

Will