MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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Steve315
Steve Brown
Burnet, Texas
(3 posts)

Registered:
09/16/2018 04:58PM

Main British Car:
1974 MGB-GT Buick 3.5l

Compression fittings
Posted by: Steve315
Date: June 25, 2022 07:30PM

What's the story on compression fittings in fuel lines? I saw somewhere that one shouldn't use them. Dug around on the web and found everything from "Don't use them" to "They use them all the time on airplanes." I was planning to use them to run the fuel and fuel return lines on my '74 MGB-GT with a Buick engine and Rover 14CUX EFI.

On a related topic, does anyone know how to transition from 3/8" tubing to 8mm tubing? I was going to use the original fuel line as the fuel return line. As best I can tell, it's 8mm. The piece of hose I brazed to my fuel tank to serve as the return port is 3/8". DOH!


waterbucket
Philip Waterman
England
(107 posts)

Registered:
07/30/2011 01:08PM

Main British Car:
1972 MGB GT

Re: Compression fittings
Posted by: waterbucket
Date: June 30, 2022 03:20PM

I have seen compression fittings on both steel and plastic fuel (diesel) pipes over the years. I have just put in new plastic oil pipe from the tank to the boiler for our central heating which uses compression fittings. The building inspector made me change the very neat 10mm soldered fittings on the oil pipe leading to our AGA because they might leak. The only thing recommended is a fuel line sealant put onto the olives to guarantee a leakproof joint, not used on the diesel engines though.
As for joining 3/8" to 8mm tubing try a fitting like this one;
[www.midlandchandlers.co.uk]
This fitting is for 7.9375mm so the olive may be a little on the tight side but it will work.


DiDueColpi
Fred Key
West coast - Canada
(1333 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: Compression fittings
Posted by: DiDueColpi
Date: June 30, 2022 08:46PM

If you are using steel lines then compression fittings will work well. If they are copper lines the copper tends to crush over time and the connection loosens up. Rule of thumb is compression fittings for non combustible fluids only though.
I prefer to use a flare fitting and make sure to use the long style forged nuts. They support the pipe connection better and eliminate pipe cracks at the flare. These nuts aren't available at your big box hardware store, you will need to hunt down a gas fitting supply house.
Some people like to use a tubing expander to make a slip joint and then silver solder the joint. I like the idea and it looks neat and tidy when done well but I worry about all the slag inside the joint.

Live like you mean it.
Fred


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