DIY Diesel Injector Maintenance

18 Mar
My disassembled diesel injector

Lately I’ve been having some issues with my inboard diesel, a trusty little one-cylinder Yanmar 1GM from the 1980’s, and since it’s such a small, light, and simple engine I decided to pull the whole thing and do a partial rebuild in my shop.

The black smoke and occasional knock I was getting told me I probably had injector issues so I taking the injector out. This was more difficult than expected as the injector is simply a press fit and was slightly rusted in place but a careful combination of PB Blaster, leverage and heat eventually freed it. Once I had it out I called a few places to see about having it rebuilt and was quoted a flat $100 for the work. Not bad considering this engine only has the one injector but still a bit more than I wanted to pay for what might end up being no more than a thorough cleaning.

One of the things I love about owning an old and uncomplicated boat is the simplicity of maintenance. This doesn’t just make repairs easier and more affordable, it also gives me the confidence to tackle any issues that arise myself. My 1GM is a good example- this engine is so basic that there is no cooling circuit, no electronics beyond a starter and a couple of sensors, and only this one injector which is supplied with a mechanical injection pump. The 1GM also has a staggeringly detailed service manual. Coming in at nearly 500 pages it covers the construction, operation and repair of every single component, including the fuel injectors. With that as a reassurance I figured I might as well try doing what everyone tells you not to and tear down the injector myself. It turned out to be an easy task to clean it up and put it back together.

Here’s the injector as it came out of the engine, with a quick cleaning

This injector is just three threaded pieces which screw together and hold the internal parts under a very specific amount of compression. Taking it apart is as simple as unscrewing the two parts from the main body casting and removing the internal pieces. There is a spring in here but by the time the threads are loose nothing is under compression so parts aren’t trying to fly out.

These are all the pieces in order. From the top: A sort of compression nut, two tiny shim washers which adjust the compression on the spring, the spring, two pieces which transfer the spring pressure evenly to the injector nozzle, the injector nozzle, and the injector tip (in this photo the nozzle is half-inserted into the tip).

There was a bit of carbon on the tip and nozzle but didn’t seem to be much in the way of gunk or varnish from the fuel, overall this injector looks like it’s in good shape.

To clean the worst of the corrosion and carbon I VERY carefully used a brass wire wheel on my bench grinder. I only did this to the less-sensitive parts such as the exterior and threads of the body pieces, I wouldn’t go near any of the internal components with such an aggressive tool.

Then I soaked all the parts in acetone. For the components where it matters the orientation is very obvious so there was no need to keep everything in order. I did separate the heavier body pieces from the internal components since the former were much dirtier.

After letting the acetone loosen things up I took everything to the kitchen and used one of my favorite cleaning tricks to get the deep grime out of these pieces- a nice slow simmer.

Gunk Soup

The parts went in a pot with a 50/50 mixture of water and simple green and I brought them to a slow boil for about an hour. Simple green and heat helps to break up the gunk but the real cleaning action comes from the bubbles and bouncing movement of the boiling water, sort of like an ultrasonic cleaning tank. Although the parts looked pretty good going in they left the water looking plenty dirty:

When I pulled them out I immediately dunked them back into my jar of acetone. It’s amazing how fast a wet piece of steel can rust and any rust on the interior of an injector would be very bad. Acetone is hydrophilic, meaning it attracts water, and it evaporates very quickly so when I pulled the parts out of my jar back at the shop they were clean and almost immediately dry.

At this point cleanliness became essential so from here on out I used clean paper and rags and wore gloves. With gloves on I dunked everything in clean diesel for lubrication and to protect it from corrosion then I laid it out in order and began reassembly.

There are a couple small tasks that are important here. First there’s the copper ‘crush’ washer which seals the compression nut against the injector body. This needed annealing before being put back in service so I heated it red hot with a torch and let it cool.

This process softens the copper so that it will make a good seal again.

Next I checked the movement of the injector nozzle in the tip. These parts are a matched pair machined to incredibly tight tolerances and any dirt, grit or corrosion between the two will cause problems. Fortunately there’s a simple test to make sure the fit good: just put the nozzle in the injector tip, pull it up by about 1/4″ and let go. It ought to drop smoothly under its own weight, and it did, so I went on with reassembly.

The cleaned parts went back in the order they came out and then I threaded the body back together and tightened it up with a couple of wrenches.

There is a pretty high torque setting for these components, 60lbs for one and 80lbs for the other, I think, but I don’t have a torque wrench which could fit them so I just snugged them up tightly by feel.

For the final and most important step I went for a drive and took my re-assembled injector to a diesel repair shop, along with the specs from the service manual. They bench tested it for me while I waited, told me it worked just fine and didn’t charge me a dime. There’s $100 saved, (I think…)!

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder


  1. Willie Osgood

    Hello Paul,
    Your article is really helpful and I appreciate your effort in writing this piece. It seems to me that it contains enough information for a DIY Diesel Injector Maintenance. I use Red Line 60103 Fuel System Cleaner to clean my fuel injector. Do you think it is okay? I will be grateful if you provide me with some more information. More details
    Thank you.

  2. Jon

    Well done, understandable article. I have a Yanmar YSE 12. I’m having a devil of a time finding the original workshop repair manual, not pdf service manual. Any suggestions?

  3. Mark

    Have you tried different injector cleaners? Wouldn’t using a $10 product be a better option than taking apart the engine? Or is it all just nonsense and those cleaners don’t do anything?

    I keep reading how you can add some of that stuff every now and again and it’ll keep the injectors working well. And some products even claim they can pretty much super-clean them inside and out with a single run through.

    If it’s that simple shouldn’t everyone just do that? I mean stuff like this:

    “cleans injectors, lubricates the entire fuel line as well as boosts cetane rating to deliver that truly optimized performance. This product works for diesel engines sporting the latest technology – such as the High Pressure Common Rail (HPCR), as well as any older systems. Cetane rating is boosted by up to 6 numbers”

    Wouldn’t everyone want to use products like these all the time?

  4. Frederick Harvey

    My 78 Hunter had its injectors sent out to be “fixed”, and they came back. That winter was a hard one here in NH, and I had left the old oil in over the winter (not a good thing), and I think running that in the summer too long until black (I had rebuilt the engine the previous winter and had new rings” which caused debris in the oil I think, and the result was “no start this spring”.

    I found could get a “turning over” by spraying some diesel into the air intake with a spray bottle, but then after a rev or two the engine would stop. So I knew compression was good enough for a start, and I also knew that when I bled the lines the fuel was at both the injectors. So my conclusion was fuel starvation, and that the injectors not releasing fuel for some reason.

    That is when I went to the web and found your EXCELLENT experience note. I decided after reading your story to take the injectors apart and I did and found two shims, not just one.

    My theory is that when injectors were sent out they came back “up to spec” alright, pressure wise, but no one told the old high pressure fuel pump with is now 39 years old, and probably too weak to push the injector open if oil is also full with new rings debris. So, I am taking the extra shim out to let the old spring work for the old pump, and I will “simple green clean, as suggested. And we will see what happens. I will leave another note. Promise, hopefully before the snow flies here.

  5. Ross G

    HI.. I took my injector apart only to find 5 shim washers in it. 3 of the originals the two others that obviously didn’t look as though they belonged.. it’s not starting and I’m wondering if there’s to much tension on the needle valve..

    Any thoughts?

  6. Mike Ford

    Can you manually test the fuel pump by pushing the plunger into the barrel by hand? I can get some fuel in when the delivery valve is out but not with it in. My Yse12 has not been started for 6 weeks and I’m at a loss where the problem is.

  7. Gregory Willard

    A friend of mine owns a big diesel truck that he drives everywhere. It’s interesting that you should make sure that you don’t have any rust on the injector when putting it back into your vehicle. I will have to find out if my friend has looked at his injector, or had it looked at.

  8. Jack

    I like your spirit,many repairs can be done by oneself,even those where others fear to tread,e.g.,the HP FI pump,but you need to take into account your skills,info & parts available and a bit of “what ifs”.
    Now,if only I could snag some detailed info on the inner workings of Raymarine instruments !

  9. Parker Reinhardt

    Our boat has a Yanmar YSE12 plus manual. My first expectation was, would last through the first year, six years later it runs fine. Simple explains it perfectly. Your article pretty well sums up my feelings. I just make sure it gets fresh oil and filtered diesel. I’ve worked on the big stuff so it is refreshing to see a 39 YO Yanmar still doing its stuff.

  10. Greg

    Yes- I agree with prior commentor
    in order to anneal copper, it needs to be heated red hot and then water quenched (just the opposite of steel).

  11. John Streatfeild

    Very interesting. I have the same engine in my 76′ Hunter. How did you come across the shop manual? Can you remove the injector without pulling the engine?

  12. Mike Ure

    The joy of owning simple things. Observation and thought allows you to figure them out, and you get tern pleasure and satisfaction of fixing them your self.
    The solution to boredom, is to own a simple wood yacht.

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