Perkins 4.108 #3 Injector Failure

[marineruscg]

I have a Perkins 4108 (westebeke trim) that is in our 1976 Pearson 365. I have no idea how many hours are on the engine... it's probably original. Anyway, last fall the #3 injector pipe failed. It just started leaking at the injector. I replaced all of them. Kept the old ones and purchased a spare #3 pipe so I'd have all new on the engine and a spare set (#1 #2 #4 used and a new #3). About 5 engine hours later the new #3 split right at the upper fitting. I put on the spare and ordered another. About 5 engine hours later the new #3 started leaking a lot at the lower fitting (tightening it only made it worse). I put on another new injector pipe and ordered a spare. Now, about 5 engine hours later that pipe is leaking at the lower fitting. We have a friend who is a pro sailboat diesel mechanic who has been helping me and he too is baffled as to why the #3 pipe keeps failing.

I have had no problems with #1, 2 & 4.

I am thinking of taking the injectors out and having them re-conditioned (I just had this done about 200 hours ago) to see if #3 might be clogged or something. If the inj are ok I guess I'll have to pull the injector pump and have it checked out.

Anybody got any ideas? I am really at a loss here.

thanks all,

capn steve

[Maddog]

Is the pipe rubbing against something while the engine is running? I know it snakes in between the block and the exhaust manifold. Just a thought.

[marineruscg]

Nope. I checked and it has clearance all around.... not much but it should be enough. I even checked the motor mounts thinking something might be moving but they're ok.

thanks for the thought.

[Cheechako]

are they breaking at the injector or just leaking....? They have little copper seal rings right?

[marineruscg]

The first new I put on split right at the 'bulge' that the fitting pushes into the injector (on the top) and the pump (on the bottom). The rest just started leaking. The pipes don't have ferrules (the little copper seal rings) they just have a formed 'bulge' at each end of the pipe.

[Cheechako]

too wierd. Is it possible that #3 vibrates while running alot? Maybe it's shape and length are setting up a harmonic or something.. can it be supported mid length somehow..? I'm grasping....

[Boracay]

Would it be possible to post a photo or two?

Does the split run along the pipe or across or some other way? Could the pipe not be running true into the injector (even tiny angle out of true may make a difference)?

Have you replaced the nut(s)? Are there any "irregularities" in the nut? Could the nut(s) have been overtightened at any time?

Do the injectors have any imperfections where the pipe is tightened on? Is it possible to replace the injector(s) with new ones?

I'd be looking at the actual split, possibly pulling it apart to look at the metal. Shiny metal might indicate fatigue, Coarse might indicate over stressing.

[CharlieCobra]

Mine kept splitting oil filters for no reason. That's why it went tits up eventually. I'll be installing a remote if I rebuild it.

[Chief Engineer]

Sounds like over tightening to me.

Is the injector tight when you snug it up?

You should be able to finger tighten them all the way befor final tightening.

Have you installed the brackets/looms that keep the pipe from vibrating.

Order of installation...install injector (loose), finger tighten pipes, tighten injectors in their holes, tighten injector nuts, on Injection pump make sure you use two wrenches to keep delivery valve from turning.

[perchance]

You may be over tightening the compression nut causing the upset on the pipe to split.

[Minggat]

The injectors do not have a fixed position. In other words, you might have that one injector misaligned. Loosen the 2 nuts holding the injector, make sure the injector can turn ever so slightly, connect the line and re-tighten the injector. You might also try swaping injectors and see if the problem follows.

[svHyLyte]

The original equipment on the 4-108 includes a bracket mounted above the injection pump and under the heat exchanger that braces the injection lines and prevents vibration that can cause fatigue cracking. If the injectors have been removed, this bracket has to be removed to release the injection lines and its possible whomever did the work did not reinstall the bracket, which is difficult, and was the case on our yacht. The effect of the bracket can be somewhat replaced with sizable nylon wire ties tightened between adjoining injection lines--#1 to #2, #2 to #3, #3 to #4, an arrangement shown to me by an old Perkins mechanic. This might help your situation.

FWIW...

s/v HyLyte

[marineruscg]

Hi all,
There are some great suggestions here. Thanks to all of you for the help. There isn't any kind of injector line support so I will be looking into fabricating something. Also, I will loosen the injector on #3 and make sure it's not putting the inj pipe 'in a bind'. Keep those ideas comin' folks... I need all the help I can get.

I'll keep you all posted on the outcome.

thanks again
capn steve