Perkins 4108 diesel leak at fuel line connections

[Mike OReilly]

I know there's another 4108 thread going with similar issues, but I have a specific leak problem that I can't seem to resolve, and I don't want to hijack the other...

The fuel lines that feed in and out of my engine-mounted fuel filter housing (the secondary) are leaking at the connections. They are steel lines which attach to the filter housing using compression fittings that consist of a sleeve and a small plastic grommet (an olive) that both slide onto the end of the fuel line.

My filter is more or less like this one:

Perkins Fuel Filter Assembly Kit

The problem is, I can't seem to make a perfect seal. It leaks at the fittings while running.

Is there some trick to making this seal work? I've cranked it on pretty hard. Perhaps I'm over-torquing and crushing the grommet? Or perhaps I need to line up the sleeve/olive and line more accurately?

[Mike OReilly]

No one? Come on folks. I know you Perkins experts are out there.

[model 10]

I installed a spin on filter. I bet you are over torquing. That is the same kind fitting I've seen used on other stuff and they only need to be snug, like inch pounds tight.

[tkeithlu]

I'm no Perkins expert, but I can tell you that I hate compression and flare fittings with a passion. Made just right (in the case of flares) and aligned just right (both of them), they work and take quite a lot of pressure without leaking. If not, nothing will stop them leaking, witness several flares in my steering system. They do not take torquing beyond what you would expect for the materials at hand. My suspicion, without seeing it but based on your description of what you've got and what you've done is misalign them and then over torque them. Take it apart and see what shape everything is in. If the collars are dinged or bent or the tubing scored or twisted then yes, you've screwed the pooch. Probably, the two tubes you are dealing with are too short to cut off, re-route, align, and compress with new collars. You're dealing with a low pressure situation; something is likely to be mangled. I don't know the size of your tubes, but likely replacement tubing is available at an auto parts store and the fittings certainly are stocked at my nearby Ace Hardware store.

[Jason Flare]

I have found that with compression fittings with a ferrule the trick is to push the pipe and ferrule into the hole and keep it straight, (by eye,) and barely snug the nut.


I don't know what to do if it's over tightened and distorted and it leaks.

Sorry. We need the person who can suggest what to do if it's over tightened.

[Mike OReilly]

Thanks guys. I'm going to zero in on the over-torque possibility. I have more olives (grommets), and I don't think I've managled the fuel line. It's 5/16" stainless fuel line running to the injector pump. The other line is a return line from the injector pump.

I'll pull the line tomorrow (too tipsy now ) and replace the olive with a new one. Then I'll reinstall with less torque.

[NoTies]

As a field fix I have had success wrapping a few turns of plumbers tape around the olive where it contacts the pipe. This is often the only way to get a seal when the pipe is distorted from over tightening.

[Kokanee]

Make sure the fuel lines aren't slightly ovalled from being bent, and have no nicks or deep scratches in them. Polish them up with some steel wool.

Also, make sure the filter housing and fittings are matching threads. It could be leaking from there. I've seen similar filter housings with UNF, UNC, BSP, and SAE threads. The fittings have to match.

[tkeithlu]

I think you have your marching orders, and should have it back in shape very soon. Think of the olive as being an 0-ring that you are pressing against the crack between the tubing and the fitting you have stuck the tubing into. That doesn't take much pressure, given the tiny surface area, but it does take cereful alignment. The tube should enter the fitting dead straight and round, and the cap thread on very smoothly.

[Jason Flare]

When I was installing my new belly tank I was reading some diesel forums online and someone referred to Teflon tape as, "The devil's toilet paper."

You don't want it in the injection pump.

[Cap Erict3]

Originally Posted by Jason Flare

When I was installing my new belly tank I was reading some diesel forums online and someone referred to Teflon tape as, "The devil's toilet paper."

You don't want it in the injection pump.

Loud second.

While Teflon Tape is great stuff I don't want anywhere near a flare or ferrule fitting

[NoTies]

Despite the fact that when properly used it works? The compression fitting use actually poses considerably less risk of getting where it shouldn't than conventional use on a thread.

[Cap Erict3]

Originally Posted by NoTies

Despite the fact that when properly used it works? The compression fitting use actually poses considerably less risk of getting where it shouldn't than conventional use on a thread.

The cost of a new fuel line complete with fittings is much less than the injector pump rebuild that would be required if a piece of Teflon tape clogs the works.

The threads on a flare or compression fitting just provide the tension for the surface area of the seal. They have no sealing surface.

[DeepFrz]

Mike, there are lots of comments on the forum about getting rid of the CAV filters. Seems as though they like to leak. No personal experience though.

[Mike OReilly]

Originally Posted by DeepFrz

Mike, there are lots of comments on the forum about getting rid of the CAV filters. Seems as though they like to leak. No personal experience though.

Yes. I'm thinking my real solution is to replace the whole filter housing. It's a PITA to change anyway. Maybe a double racor on the engine room bulkhead. Right now I have a single, which is the primary.