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


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