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Old 08-05-2021, 02:57 AM   #1
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Cummins VT555 low power & smoke

Hi, I'm trying to resolve a power loss issue on our VT555 and would appreciate any advice as I'm new to this engine. I've reset the injectors and valves as per the book and it runs sweet, and no smoke even at high RPM untill we put it under load. Turbos can be spun by flicking with the finger, but one of them is getting pretty hot, not enough to fry an egg but heading that way. Going to look at the elbow to see if sea waters leaking today.
Any ideas what I should check thro would be real welcome!
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Old 08-05-2021, 04:57 AM   #2
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Under load, the exhaust is black and excessive? A faulty turbo or other loss of boost would be my first guess. Any chance of getting a pressure gauge on the intake to see how much boost you are getting?


Did all this happen before you reset the valves and injectors, and you did those steps trying to correct the problem? Or did you otherwise make those adjustments, and now this is the result?
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Old 08-05-2021, 11:15 AM   #3
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Not sureWe had mechanic on the job, he recommended changing the injectors, but he made it worse, even bent pushrods, so I was asked to check it over, finding he hadn't started at TDC Cyl. 1, so messed it up. I did it by the book, and there's no smoke at idle now, only under load. It's grey smoke.
There is also pressure feeding back into the tank, and this may be the new injectors which don't have the flattened rubber rings, but skinny round ones.
Maybe leaking gas back into the fuel feed.
I'm not sure how to check intake pressure though, is there a guide?
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Old 08-05-2021, 04:39 PM   #4
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Boost pressure needs a boost gauge connection or port on the air supply manifold somewhere between turbo and cylinders. Boost reading would help.

On old injectors what did the sealing rings look like? Mine were typical round diameter,. Not
Square . Mine were a brown colour. There are two types, black and brown. Mine were replaced with brown rings. I needed to apply a fair bit of pressure to get them into place. The injectors body was well oiled with assembly lube before installion.

Was the copper cup in the head cleaned? Need a clean rag soaked in solvent and a wooden dowel as a tool. NO METAL. Took me at least 5minutes per cup. Dowel end should be shaped to cup shape or close. Damage to the cup ! means pull the head.

Pressure in the tank? What do you ! mean? specifics. How are you determining this?
These engine pump upwards of 80 + gal per hour returning about 75 - 80%
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Old 08-05-2021, 05:39 PM   #5
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Hello, Robby - I’m always interested in anything to do with Cummins 555 engines, as we are the new owners of a 1986 Hershine 42 (bought from the original owners this summer) with the original engines in it. I hope you find your answers here.
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Old 08-05-2021, 06:47 PM   #6
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Quote:
Originally Posted by Robby View Post
Not sureWe had mechanic on the job, he recommended changing the injectors, but he made it worse, even bent pushrods, so I was asked to check it over, finding he hadn't started at TDC Cyl. 1, so messed it up. I did it by the book, and there's no smoke at idle now, only under load. It's grey smoke.
There is also pressure feeding back into the tank, and this may be the new injectors which don't have the flattened rubber rings, but skinny round ones.
Maybe leaking gas back into the fuel feed.
I'm not sure how to check intake pressure though, is there a guide?

Perhaps it would be good if you could go back to when the boat last worked properly, and tell us the whole story that got you to now. New injectors and bent push rods are pretty significant elements that were missing from the first account.
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Old 08-05-2021, 08:50 PM   #7
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Also, what are the signs of power loss? In other words, can you describe what strikes you as unusual about what you hear, see, smell, and feel about the boat, the way it moves, and its impact on the world around it, e.g. sound, Smoke, vibration, rpm, and ground speed, and what operating conditions these symptoms appear, quantifying or providing comparative references for as much as possible, e.g. 3000rpm, or rising (vs lingering) grey smoke without any blue hue that is visible for 15ft st 5kn or whatever.


ow RPM? Low water speed? GRE
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Old 08-06-2021, 09:20 AM   #8
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The push rods got bent by adjusting them at the wrong points, early history I don't have, they say both engines were fine for years, then started smoking, so a mechanic said he'd change the injectors. Don't think he was really in top of the job if you know what I mean.
Engines sound good, port engine has heavy pressure build up in it's tank, and the "new" injectors have skinny red seals that are too thin for the groves. Looking for new ones now.
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Old 08-06-2021, 09:23 AM   #9
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Thanks, me too, would be good to get this fixed.
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Old 08-06-2021, 10:19 AM   #10
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The original rings fully filled the grooves, they're black, oval shaped. One tank is getting enough back pressure to spray fuel out of the vent, they'd overfilled the tank, right to the cap.
I'll check the book and fing the pressure connection, and buy a Guage.
I'll check the cups in the head next
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Old 08-06-2021, 04:35 PM   #11
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To be clear here I am not a V555 mechanic. I do though have one and have had for many, 35 yrs, and about 5,000 hrs. of my own and about 7K hrs on the engine, so have gained some good experience by doing my own work on the engine, an N/A version, not turbo.

I did my injectors in 2019.

Do you have twin engines or a single?????? Not clear.

*****The original rings fully filled the grooves, they're black, oval shaped.***

The real O rings are a round cross section, NOT OVAL. They get that ovalness from being squeezed into the groove and by tight fit in the bore of the injector bore. That is absolutely normal for O rings, all types. The squeeze changes the shape by forcing the ring to nearly fill the groove. After many heating cycles and years they assume that shape permanently. The ring needs about a 10% compression of the diam, to effect a seal reliably, maybe more in this case.

*****One tank is getting enough back pressure to spray fuel out of the vent, they'd overfilled the tank, right to the cap.*****

Take some fuel out of the tank OR if you have a balancing line open it so some of the fuel will transfer to the other tank. Just check the other tank level. Back pressure could be from a plugged vent line , insects build nests in the vent line or hull fitting sometimes OR a kink in the line closing the hose bore OR a hose that is failing and the inner liner has let loose of the exterior and is closing , at least partially, the hose so air cannot get out or in.

If the tank is filled to the cap Reduce that fill.

Two tanks?????????/ If both feed valves are open to the engine feed it could be pulling from both tanks. If one of the return line valves is closed down, maybe not fully off though, that could force the bulk of the return fuel to the spraying tank.
Examine closely the valves for both the feed lines AND the return lines.

I was serious about the amount of the fuel that PT pump moves. What ever the engine is rated to burn it will flow at least 5X that quantity.

And by the way the coolant must be drained or when you pull the injector to check the cup coolant will fill the cylinder. TO be clear in this case I drained mine just to be safe. My book does NOT say one way or the other.

I have added the parts manual which may help although it is for a NA engine.
I will also add the owners manual but it may be over a couple replys.

HMMMM! the attachments won't load. FIles may be to big. Try sending me a PM by clicking on my forum name including your Email address.
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Old 08-06-2021, 06:44 PM   #12
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Thanks, that's very useful, didn't think about the rings squashing, makes sense. I'll check the vent lines for blockage, and get the level down to keep the fill tube empty.
I'll was thinking a bad seal was feeding exhaust gas back to the tank as the fuel is getting warmed.
Not sure I understand about the coolant though, how does that leak if the injectors removed?
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Old 08-06-2021, 08:27 PM   #13
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****Not sure I understand about the coolant though, how does that leak if the injectors removed?****
There are three O rings on each injector. Bottom one and the centre one seals the fuel , top one and the centre one seals the coolant. I am not sure about this so be safe and drain the coolant if you start pulling injectors. If you do need to drain the coolant and you do not you will fill cylinders which will make the job far larger and more damaging to the engine.

****I'll was thinking a bad seal was feeding exhaust gas back to the tank as the fuel is getting warmed.****

The fuel is actually used to cool the injectors. Yes, it will get very warm, almost hot. The tanks then act as a reservoir to cool the fuel down. But even the tank will get warm. This is quite common on many engines. If the fuel gets too warm the builder will install a fuel cooler. Unless you run the engine LONG, LONG hours at high power that should not be a problem.
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Old 08-07-2021, 04:49 AM   #14
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That's good to know! I'll be spending more time to revise the procedures.
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