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How Not To Do It With Diesel Engines

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Just about every time you pick up a boating magazine you read about “how to do” any number of repairs. These articles are great at instilling self-confidence. But I’m going to talk about the other side of the coin: how not to do it. And trust me, I’ve had plenty of experience. I certainly can’t cover all of my mistakes, but I’ll give you a running start in the diesel department.

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Bleeding Diesels

Proper British gentlemen call their engines “bleeding diesels” when they want to call them “damn diesels” but are too proper to do so. I’ve never had that problem when talking about my diesels or anything else on my boats. I use the term “bleeding diesels” to describe one of the procedures you may use to remove air from the fuel lines to try to start the engine when it won’t. There’s no point in going into all the right things to do. They’ve been widely covered.

No matter how “right” you do it, you’re going to wish you left it to a mechanic if you crank the engine too long while trying to get the diesel fuel to come out at the injectors. Consider this: When you turn over most marine engines that are below the waterline, you’re pushing raw cooling water through their plumbing. It has to go somewhere. Normally it goes overboard by entering the exhaust at the nipple on the riser, then into a muffler; if the engine is firing, it is blown out the exhaust line by the pressure from the firing cylinders. Along the way it cools the exhaust line.

But there’s the rub: Often when you’re trying to bleed a diesel the thing isn’t firing, at least right off. And if you turn it over enough the raw water pump may push water through until it fills the muffler. It then may even trickle back down through the exhaust manifold to the top of the pistons. This isn’t how to do it.

I once saw someone turn off the raw water intake through-hull to prevent this from happening. What did happen was that the pump’s impeller quickly stripped, and when the engine finally started he had a new job with which to entertain himself. It didn’t help that, as with most installations, he couldn’t even see the pump, much less change its impeller. He had to remove quite a few engine parts so he could get to the pump and then had to remove the entire pump. This is not how to do it.

A better trick, in my opinion, is to remove the water hose from the injection nipple on the riser and stick it into a big bucket to collect the water. Of course, don’t do this and leave the scene; as long as you’re watching what you’re doing, all is well. The water goes into the bucket.

But there’s also exhaust and soot that billow from that nipple. This stuff isn’t going to settle in the bucket. And if you have a clean engine room — I’ve heard some are — it won’t be clean for long. Worse, if the engine fires for more than a brief moment you may burn up the inside of that expensive exhaust hose. The trick is having a helper at the helm to shut down the engine if it starts, and having good ventilation to keep you healthy down in the engine space. This is how to do it, although I said I wouldn’t go there.

Bogart That Joint

Seafood à la manifold can impede the passage of cooling water, which can lead to all sorts of trouble.

Diesels have joints with which you just don’t mess. I’m referring to the joints where the high-pressure fuel pipes are mated to the injectors and the injector pump. With many engines, you have to loosen the joint in the bleeding process so that air and then pure fuel bleed through. But don’t loosen it to the point where the threads separate. Just loosen the threads enough so that air and fuel seep, not flow, through.

If you disconnect the threads, odds are that you’ll have one HOA (as in hell of a) time getting them to mate again. This is because the threads are fine and the pipes rigid. If you force them you’ll strip the soft metal of the pipe ferrules. This is not how to do it. (I discussed how to remate threads in the October 2015 issue’s Sea Savvy.)

Even if you have to remove an injector from the head to inspect the tip or look into the injector port, do not remove the pipe from the injector unless it’s absolutely necessary. When you reinstall the injector you’ll have the same thread problem discussed above. In most cases you can carefully remove the injector from the port — perhaps tap it to loosen the carbon deposits — and loosen the compression fitting on the injector line so that the injector can turn and you can inspect the tip and look into the hole. Don’t disconnect the injector entirely from the fuel line.

However, it’s also important to not bend the pipe. This is very easy to do because it’s made of soft metal. If you bend it even a little, you’re going to have a miserable time reconnecting it to the injector or pump, and you’ll weaken that pipe. This weakening may not be enough to make a difference during the life of the engine, but sometimes a pinhole can develop in the crimped area. A pinhole leak in a high-pressure fuel pipe can produce a fine spray of diesel in the engine space. Typically this will be while you’re underway, and you won’t know it. You’ll be up enjoying your day until that fine diesel mist, which is fairly flammable in this condition, ignites from a hot manifold, a spark from the generator or some other source. And as long as the diesel is running, the fire is being fed this explosive mist.

This is not the way to do it. Unless you have a very good fire warning system in your engine space — and it’s critical that you do — you may hardly have time to jump overboard.

Dribble and Spray

We often see advice regarding the tips of diesel injectors. These are typically called atomizers because their job is to reduce the fuel that is being fed into the injector under high pressure to a very fine spray as it goes into the cylinder in the firing sequence. The spray must be in the correct pattern for proper combustion, and dribbles won’t substitute for this.

When your diesel starts losing power, emitting a lot of black smoke from the exhaust, or exhibits other bad behavior, we are told that the injectors could be fouled. A really bad injector can allow fuel to get into the lube oil. I’ve seen injectors so crudded up that it’s a wonder the engine ran at all.

So we are often told to pull the injectors and take a look. If we see black crud cooked onto the injector tip, we can assume that the spray isn’t in the correct pattern or, worse, that it’s more of a high-pressure dribble than a spray. This means that the fuel isn’t burning completely and the cylinders and pistons are also getting wonderfully crudded up.

If you follow this advice and pull the injector, it may be best not to disconnect it from the piping for the reasons mentioned above. Anyway, the idea is to turn over the diesel so that the injector pump can pressurize the atomizer and you can observe how the diesel comes out. This is something that’s usually done by a qualified mechanic because we’re not going to really know how to gauge what we see. And diesel mechanics use special bench equipment in a shop to perform this test.

But when we’re at sea and having problems, we don’t always have the “how to do it” manual. If your diesel is indicating a potential injector problem and you’re making a passage, you may decide to divert many miles into port to find a mechanic. Or you may feel inclined to pull the injector and plug on.

But here’s the issue: Not only will the the injector and its spray pattern have to be obviously out of order for you to see that there’s a problem, but there also can be great danger in pulling injectors. First, the spray may explode if there is an ignition source. Also, if you aim the injector toward your skin, the pressure behind the spray can be so great that the fuel can penetrate your skin. You don’t even want to think about the health consequences. This isn’t how you do it.

Maybe under some rare circumstance you should consider checking your spray, but it should be as a last resort and under the duress of serious consequences if you don’t. And you must have the procedure very well planned out. I should add that I’m not referring to common rail diesels, which require very different tactics and have extremely high fuel pressure in the rail.

When winds are fair and sails are up, you won’t even think about how not to work on your diesel.

Culinary Terrors

If your boat has one of the many engines equipped with cast iron raw-water-cooled manifolds and risers, you live a life of constant terror. At least you should. That’s because on any given day the rust inside the cooling passageways might make its way through the wall and allow water into the engine block. And to make matters worse, all that heat is cooking marine life inside the manifold.

Whether you like well-done seafood or not, the fact is that the seafood, when cooked onto manifold walls, has a tendency to impede water passage, making more heat, even more cooked seafood and a greater likelihood of heat-induced cracks in the manifold. This can happen even if you boat in fresh water, although hopefully without as much frequency.

Wise men say to change these parts every five years or so. Wiser men suggest greater frequency. Terrified men say do it every two years. But the know-it-alls, such as me, say, “Aw, you can just pull it after five years, boil it out, maybe clear it with a little muriatic acid, and put it back on clean and ready to go.”

Always one to follow my own advice and wish I hadn’t, I did this with my first Perkins diesel. I even went the extra mile and used the muriatic acid. I was really impressed. It looked clean and new, but there were still a few morsels of well-done seafood on the walls. I think it was steamed baby clams. Before I put it all back together I scraped these imperfections off with a screwdriver. Never do anything halfway.

I scraped right through the wall, which I guess I had weakened during the cleaning process. I wouldn’t have had more than a few hours with that manifold before the water would have flooded through the walls. This was not how to do it. When you consider the cost of replacing an engine and the cost of replacing a manifold, the call is pretty obvious.

This article originally appeared in the May 2016 issue.


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