O-ring sealed fuel pipes

[HATT 46]

A local DD dealer recommended the O-ring sealed fuel pipes to replace the flared tube design fuel pipes. Is this a DY project. Do you have to do a comlete engine tune-up after installing new pipes? Any other thoughts. Thank you in advance.

 

[Genesis]

Ok, couple of things.....

First, to replace these, you need either new injectors (with the proper fittings) OR you need to remove and replace the fuel pipe connections. You also need to replace the connections on the head.

You CAN do this yourself, but I don't know if I would. Why are you replacing the flares? They're perfectly ok if not abused. When you remove them, put them back in the same place and position (end for end) that you removed them and torque to spec.

I've got the O-ring versions and they work fine too, but IMHO there's no reason to change the other ones out unless you're doing a major or something and the head and injectors are both being replaced anyway. Then I might......

What was the local DD dealer's reason for recommending this (other than selling you the parts, of course!)

 

[captddis]

If changing injectors or disturbing the jumpers I would go with the o ring style, they come in a kit with everything you need. Much safer and reusable. The flare style should be replaced whenever removed. However if yours are fine then I probably would leave well enough alone. Ps the kits are on e bay right now.

 

[Genesis]

The flares fail because idiots overtighten them. You MUST torque the pipes, which means you MUST have the split-socket and a torque wrench. The torque spec is EASILY exceeded with a box-end wrench.

If you just tighten them up with a wrench you will split the flare and it will leak, diluting the oil, which is very bad if not caught quickly.

A leaking fuel pipe is detectable by removing the valve cover - the junctions that DO NOT have oil on top of them are leaking (the fuel washes it off)

 

[TedZ]

In my world fuel and brake lines are always double flared...prevents cracking the flare 100% of the time and you do not have to be as careful over tightening. O-ring better however, no doubt.

Ted

 

[captddis]

The flares are a one time deal. I have had them split torqueing them the first time. No dealer will re use them ,nor will I . Way too much risk. I have seen new boats catch fire with the flares. That is why DD came out with the o rings.

 

[Banshee36]

I think I am missing the boat here. The o-Ring fuel lines, I have are on my engine. The things I do not like about them are ;a) They are made of good old steel and they rust, b) they are quite expensive. Plus if you loose one of the o-rings you could be SOL . On my boat to change out the impeller, you have to take the fuel system apart. Major PITA.
JW

 

[Genesis]

Oh, and the O-rings are quite expensive - something like a buck apiece. DD of course does not publish the specification which would enable you to get them from somewhere else for a couple of pennies - if that.

I have the O-ring fuel pipes on my boat, but would have no problem owning one with the flares - but I do my own work and nobody gets to "ape" my fuel system.

If you KNOW nobody has ever "aped" a flare pipe it can be reused provided you put it back in the exact same position it was originally (orientation and position.) Mark it before you remove it. Some people change them any time they're disturbed as additional "insurance" but insure it doesn't if they're not handled properly. A lot of guys freak out when they see the older flare fuel pipes but its never bothered me and I've never had a problem with them. Then again I'm not afraid to use a torque wrench everywhere its supposed to be used.

Part of your checks ANY time you disturb anything under the valve cover should be to start up with rags over the rocker arms (so you don't get an oil bath) and check that everything is ok. A cracked fuel pipe leak will be obvious if you do this. If you work on a Detroit and slap the valve covers back on when you're done without checking your work, IMHO you're asking for it - and one day you will get it in the form of a governor that slams the rack wide-open on start and leaves it there!

BTW, o-ring "sealed" fuel pipes can leak too. A tiny piece of grit or a hair on the sealing surface can compromise the seal. So can re-using the O-rings; good engineering practice is to replace any O-ring that has been under pressure when it is disturbed.

If a flare pipe cracks on initial installation it is due to grit being in the seal area or a manufacturing defect - assuming you don't overtighten it.

 

[Will]

Everything above rings true;
Flares work fine when properly torqued.
O rings are preferred but the difference isn’t enough to make it worth while converting from flares unless you are there anyway.
If you have messed with the fuel system under the valve cover, ALWAYS run the engine and check for leaks before replacing the cover.

Now I would add:
Check your lube oil periodically (quarterly for me) for signs of fuel dilution. It doesn’t happen frequently but when it does, it’s good to find the source and repair it. This can be checked when pulling the dip-stick by:
A. The smell test. Some folks can smell raw fuel in lube oil even with all of the other unpleasant ingredients.
B.The rub test – Rub a bit of oil from the stick between your fingers. If you have done it enough to know what it feels like normally, you will notice that the oil is less slippery if there is fuel dilution.
C. The drop on a paper towel test – If you put a drop of oil on a paper towel and watch it spread, you’ll see a difference between good oil and diluted oil.
In any of the above tests, the difference between diluted oil and good oil are easy to see and will cause suspicion long before the dilution becomes dangerous. If in doubt, compare test results between your two engines. Or, call your DD guy.

Will

 

[HATT 46]

Thank you all for the feedback. Reason for changing to O-ring sealed fuel pipes is that I noticed a slight(?) increase of 1/16"to 1/8"? above the full mark) in the oil level after a 7-8 hour run and a drop in the LO pressure to about 35-40 at 2000 rpm. Port engine read a steady oil pressure of 50.
When I looked at the fuel pipes where they contact the connectors I noticed that some had puddles of oil, as they should, and some did not. I replaced those that did not (14 lb-ft torque) changed LO and filter and after a 6 hour run there was no drop in the oil level, which is unusual for Detroits. LO pressure was somewhat better, 40 to 45 range, but not constant. Is there any other place(s) where fuel can leak and find its way into the crankcase? Thanks again

Michael

 

[captddis]

Sure, The injectors can leak or the other fittings. Shut off the fuel valves, hook up a hand primer pump and pressurize the system to 70 lb. . Then watch for leaks. I bet something shows up.

 

[Genesis]

Yep. There's actually quite a few places that fuel can find its way into the oil, but nearly all are under the valve cover.