Buy rebuilt injectors OR rebuild myself, 1983 300D

The problem with injector leaks may be a little over rated. We have sold thousands of nozzles and hundreds of rebuilt injectors. Of course the only time you hear back is when there is a problem. We have probably had less than a dozen reports back on problems with persistant injector leaking.  Most are due to improper, cleaning, lapping and over torquing. When it comes to working on injectors a "little extra" on the wrench is not a good idea. Other leaks are caused by removing an old over tightened injector and upsetting the pre-chamber ring seal. And leaks can be caused by over-tightening an injector back into the head. So you can see that even if you buy brand new injectors there is still the chance you might have a leak (although not from the injector halves you hope :-)

There are five different places where the injectors can leak fuel. So the first thing is to make absolutely certain where the leak is originating from. This will require use of carb cleaner and compressed air to thoroughly clean the injector and surrounding area. Start the engine. Use a flash light and inspect for leaks. If they don't show up right away drive the car a couple blocks and inspect again. I have seen cases where the injector hard line connection or the return fuel hose is leaking fuel down the backside of the injector and giving the false impression it is leaking at the base.

If you plan to be involved with Mercedes diesels for a long time you probably are best served by learning how to rebuild and test them yourself. You will have the knowledge to clean and retest in the future.  Of course installing rebuilts is the quickest way to go if you don't have the time or inclination.

Summary of where leaks occur:

1. Leaks at the hard line fittings. The ball ends of these lines wear and even rust. If the leak is originating at the top of the injector try loosening and then re-tightening the fitting nut a number of times to reseal it. If the leak persists the line could actually be cracked (common due to vibration). Replace the hard line.

2. Leaks at the return hose connections. These are common and usually due to trying to reuse the old rubber hoses. Always replace these hoses when you change the injectors. If they have been recently replaced and are long enough try cutting off 1/2 inch and re-attaching. Slight leaks from these hoses can appear as if the injector halves are leaking.

3. Leaks at the injector halves. This is usually due to improperly fitting parts, insufficient lapping, lack of cleanliness or improper torquing.  And yes, you do not want to over torque either. This can distort injector parts and make the leak worse. Remove injector and redo cleaning and lapping procedure. If you still have just a little fuel weeping out of the halves you can clean the area with carb cleaner and compressed air and "wick" thin thread locking compound down into the grove between the two halves to seal the threads. Do not use too much thread locker.  I have also had some success using a small amount of thin super glue (sparingly). Note: Don't try to use thread compound with the injectors apart. You do not want to get the compound down inside the moving parts of the injector.

4. Leaks between the the injector and the threads of the pre-chamber. This is caused by engine compression pushing unburnt fuel out through the threads. The fuel should be burning in the chamber if the engine has good compression and the engine injection timing is correct. If that is not an issue replace the heat shield washer begin careful to thoroughly clean the chamber seat.  Do not over tighten the injector.  Some seem to think if you just keep tightening the injector the leak will stop - but that will just deform the heat shield and possibly even the nozzle itself.

5. Leaks between the pre-chamber and the cylinder head. There is a crushable sealing right under the pre-chamber. With age and the abuse of over tightening injectors these sealing rings can loosen up and fuel will leak past the ring and up the side of the pre-chamber.  Removing a pre-chamber requires a special nut tool and a special slide hammer threaded.  You will need to factory manual to learn more about removing and replacing a pre-chamber.

I am new to this website and soaking in a lot of helpful information. I am curious to know what halltyler decided to do and how it turned out as I am facing the same question for my smoking '82 300SD that just hit 200K.

Since the post was over 8 months ago I doubt if you will get a reply from halltyler. Our records show he did order a set of rebuilt injectors. If you have any other questions on injectors post them here and I will try to answer. Kent Bergsma

Thanks Kent for the interest. OK maybe you can help me out in this decsion process - Assumming my experienced benz diesel mechanic charges $50 per hour and he will be installing the nozzles or the complete rebuilt injectors out of the box how long should it take him to perform either task? I.E. everything else being equal do I come out ahead by paying more for the complete injector or having him install the nozzels?

Has your mechanic rebuilt diesel injectors before? Does he have a pressure tester and the correct equipment to set the balance pressures during overhaul? You should ask him what he charges for either job. He should be able to give you a fixed price estimate. From my experience, unless YOU are doing all the work yourself, it is usually cheaper to go with rebuilt injectors.

I attempted to rebuild 5 injectors with the Monark nozzles:

great kit, very good instructions, and I purchase the new heat shields, return lines, and a necessary torque wrench . . .

a little bit time consuming, accuracy to detail is a must!

Hindsight -- I would purchase the rebuilt injectors from mercedessource and trade the old injectors for core refund.