Teflon tape around injectors? - PeachParts Mercedes-Benz Forum

cirrusman · #1 05-28-2012, 03:13 PM

So my injectors 1, 3 and 5 were leaking right where you plug them in the engine, leaving a terrible smell of diesel in the cabin every time I turn on the vent, so I decided to fasten them a bit more. The result was that injectors 1, 4 and 5 are dry and 2 and 3 are leaking just the same. I really don't want to over torque these babies and that's about as tight as I really want them. I'm thinking about wrapping around some Teflon tape on the threads, the type you use on plumbing, maybe 1 or 2 layers, you guys think this would be safe or would it hurt things in the engine? The other option is the blue sealing stuff, but I'm not sure that's really going to do anything to solve the problem...
Whaddya guys say?

TheDon · #2 05-28-2012, 03:19 PM

They are probably leaking from where the injector halves go together or the hard lines o top. But usually they leak from the return lines.

cirrusman · #3 05-28-2012, 03:25 PM

Thanks TheDon; I checked that... the injector bodies are dry, hoses are dry (until I took them off to tighten the injectors), no fuel coming off the halves or the hoses; there is, however, fuel coming off where the injector meets the block, with little bubbles and everything to clear any doubts.

sixto · #4 05-28-2012, 03:40 PM

Spring for a new set of injector seals/heat shields and don't tighten more than spec (70Nm?). If leaking persists, it might be from tired washers between the prechamber and head rather than injectors sealing against the prechamber.

Sixto
87 300D^2

cirrusman · #5 05-28-2012, 03:46 PM

Well, funny thing: I let the engine cool a bit, sprayed some break cleaner around the injectors to track exactly where the leaks come from, and now injectors 2 - 5 are dry and #1 is leaking bubbles. Talk about Murphy's law.
Sixto, I've got the extra heat shields last week just in case I'd need them for something like this; I just want to check whether teflon tape would hurt the engine. I've searched the forum and a couple of people have suggested it in the past but nobody has an opinion as if it would be a good or a bad idea.

sixto · #6 05-28-2012, 04:06 PM

Try it. See if teflon tape survives torquing to 70Nm. I suspect it'll get shreaded. The next thing is temperature. A cylinder head gets far hotter than typical home and business plumbing. A quick internet search shows teflon tape is good to 250-500*F (take your pick). I would think a prechamber routinely sees 250*F, though maybe not 500*F.

Sixto
87 300D^2

Jeremy5848 · #7 05-28-2012, 05:12 PM

The threads don't do the sealing (they're not pipe threads) so Teflon tape isn't the answer. The leaks sound like they are between the prechamber and the head or between the injector body and the prechamber. Given the pressures in a diesel combustion chamber, cleanliness of the sealing surfaces is critical. Use fine steel wool to polish the points where the injector meets the prechamber. Don't disturb the prechamber if it hasn't been recently removed from the head; it's probably OK. Suck out any debris with a vacuum cleaner. Re-install the injector with a new seal -- never try to re-use an injector seal.

Jeremy

Zacharias · #8 05-28-2012, 05:24 PM

A bit more background info would be useful:
- did you recently have the injectors out of the car?
- if yes, did you install new heat shields when you reinstalled them?
- if yes, are you certain you installed the heat shields right side up?
- are you certain you removed all the old heat shields before you installed the new ones?

Not being rude with the last question but I've seen it done....

Brian Carlton · #9 05-28-2012, 05:25 PM

Quote:

Originally Posted by Jeremy5848

The threads don't do the sealing (they're not pipe threads) so Teflon tape isn't the answer.

X2.

cirrusman · #10 05-28-2012, 06:58 PM

I do appreciate your guys' inputs

smiffy6four · #11 05-28-2012, 07:06 PM

Say no to teflon. It's for plumbing.

Diesel911 · #12 05-28-2012, 08:06 PM

Where these Injectors recently tanken apart.

Over tightening the Injector halves often splits the Injector Nut; sometime they do not spilt right after tightening but split on down the Road.

The cure for leaking Injectors between the Injector Nut and the Upper body of the Injector is to take the Injector apart and properly lap the precision surfaces.
Clean them and assemble them properly.

cirrusman · #13 05-29-2012, 10:39 AM

The injectors were taken apart in August of last year and a set of new Monark Nozzles was installed professionally in each injector, which I proceeded to install in the car. The injector halves are dry, there are no leaks from the halves or the return lines are tight nad dry too. The heat shields were installed correctly (the leak just started a couple days ago) and now it's only injector #3 giving me trouble. By your guys' responses I think there might be some dirt still left in the threads, so I'll clean that up good and see if that fixes the problem, but I will stay away form teflon. I appreciate you guys pitching in with your valuable opinions!

Diesel911 · #14 05-29-2012, 09:52 PM

Quote:

Originally Posted by cirrusman

The injectors were taken apart in August of last year and a set of new Monark Nozzles was installed professionally in each injector, which I proceeded to install in the car. The injector halves are dry, there are no leaks from the halves or the return lines are tight nad dry too. The heat shields were installed correctly (the leak just started a couple days ago) and now it's only injector #3 giving me trouble. By your guys' responses I think there might be some dirt still left in the threads, so I'll clean that up good and see if that fixes the problem, but I will stay away form teflon. I appreciate you guys pitching in with your valuable opinions!

No where on or on the Injector or where the Injector goes into the Engine do the Threads do any sealing.

You can get dirt on either side of the Heat Shield and that can can keep from sealing down there.

It is also possible even if the internal parts of the Injector were lapped for something to get between the surfaces before assembly. It does not take much; a piece of Rag lint would do it.

Jeremy5848 · #15 05-30-2012, 12:12 AM

Quote:

Originally Posted by Diesel911

No where on or on the Injector or where the Injector goes into the Engine do the Threads do any sealing.

You can get dirt on either side of the Heat Shield and that can can keep from sealing down there.

It is also possible even if the internal parts of the Injector were lapped for something to get between the surfaces before assembly. It does not take much; a piece of Rag lint would do it.

Absolutely right! It is impossible to emphasize the importance of strict cleanliness in cleaning, lapping, and assembling a diesel injector. Only the metal surfaces do any sealing since no o-ring could withstand the heat and pressure. A class 100 clean room would be appropriate; would that I stolen one of those instead of office supplies.

Jeremy