CUMMINS 555’s

While this injector style may be old , Detroit used it in 1936 and up it may be making a comeback.

Small comercials of the world are not in love with $1,000 injectors or a boat that stops for a bad transistor.

These injectors can be sized to the specific boats operational use and may with DEF finally allow modest sized engines to make the air police Tier 10m ,Tier 20, whatever, happy.''Fingers crossed , imagine repairable engines again!

I get the whole unit injector design, but reiterate I am a total amateur with the specific designs and variations. I have looked pretty closely at Scania's current unit injector design since I'll be using it, but that's the only one.

I thought that all injector "tips" have pressure activated valves at the end. That's what ensures a build up of pressure before they spray, and enough pressure to get a good spray pattern. The pressurized fuel may come from the plunger in a unit injector, from a high pressure common rail pump, or from a conventional injection pump. But in all cases, you need to hit the injector nozzle with high pressure for it to open. When injectors are tested, the pressure at which they open is tested, as well as the resulting spray patten. So given this, I would have thought that pressurized fuel would be required to push any past an injector nozzle, regardless of the injection system type. I didn't think there was ever a case of any sort of open valve that could result in fuel flow unless the fuel was also pressurized to injection pressure, which is way higher than he head pressure of any fuel tank

Is this not the case? Again, I'm no expert. But maybe one of our diesel gurus can help out here?

I don't know about a comeback but it was a good system. Maybe it can be adapted with electronic controls. Will be past my time.

I was thinking about the flooding some more and thought of another way to flood the engine.

Not through the pressure fuel line but rather by the fuel return line.

It would take a few things to be present in the boat and the tank plumbing:
--a goofy tank atmospheric vent as mentioned.
--a return line dip tube that goes below the fuel level. Many boats are plumbed so the return line goes to a dip tube that nears the tank bottom to avoid aeration of the fuel. These engines return a lot of fuel so aeration could be a problem.
--a failed return line check valve. There is one on the R.H. cylinder head at the back of the engine. It's about 1.25" diam and 3" long. Intended to hold fuel in the heads so the fuel does not drain back to the tank which can cause hard starting requiring lots of cranking. It does show in a parts book. I had to replace mine ~15 yrs ago for hard starting.
--maybe a fuel level higher than the engine.
--maybe a leaky injector.

If there is a venting problem AND a check valve problem maybe the fuel could back track to the engine from the:
--check valve allowing fuel back. It should not if working well.
--from pressure from a pressurized tank even though low pressure. Fix it.
--a return line dip tube below the fuel level.
--maybe tank fuel level higher than engine. With a return line dip tube this would not be needed as long as the dip tube remained below the fuel level.

Look for that check valve and replace it. Cummins P/N 178079

If you have not yet gotten a v555m parts manual go to Boatdiesel and join so you can download the Owners and Operators manual and the Parts book I posted years ago. The Owner/Operator manual is posted in 5 parts. The parts book is the sixth.

I would suggest that you also keep an eye out for a used set from Ebay but the above will help a lot.

As suggested you should be perusing Ebay also for an operators manual

Scania and Deere both have current model tier III maine engines that utilize unit injectors. They are electronically metered and timed, but it's the same fundamental concept with a cam driven unit pump to reach injection pressure.

twistedtree said:

I get the whole unit injector design, but reiterate I am a total amateur with the specific designs and variations. I have looked pretty closely at Scania's current unit injector design since I'll be using it, but that's the only one.

I thought that all injector "tips" have pressure activated valves at the end. That's what ensures a build up of pressure before they spray, and enough pressure to get a good spray pattern. The pressurized fuel may come from the plunger in a unit injector, from a high pressure common rail pump, or from a conventional injection pump. But in all cases, you need to hit the injector nozzle with high pressure for it to open. When injectors are tested, the pressure at which they open is tested, as well as the resulting spray patten. So given this, I would have thought that pressurized fuel would be required to push any past an injector nozzle, regardless of the injection system type. I didn't think there was ever a case of any sort of open valve that could result in fuel flow unless the fuel was also pressurized to injection pressure, which is way higher than he head pressure of any fuel tank

Is this not the case? Again, I'm no expert. But maybe one of our diesel gurus can help out here?

Click to expand...

I'll take a bit of a stab.
The PT pump supplies fuel to the cylinder heads in a gallery common the all injectors. It is pressurized to several hundreds of pounds but varying depending upon engine speed. When the injector is actuated there is valving internal to the injector which isolates the the injector from the gallery and then pressurizes the fuel as it injects up to ~ 20,000psi. At a certain point another valve function bleeds excess fuel back to the return line.
Unlike the more common injector pump the real pressure is developed at the injector from the camshaft.

Paul Foulston had a name for the action, which I cannot remember, but it was fast, abrupt and effective.

I have read the operation but it was a long enough time ago now I don't remember all the details.

Excluding the 555 OP dilemma for a moment -

My engines, not unusual to most marine diesels, has a lift pump feeding the on engine filters and in turn the injection pump. Fuel tank level when more than 1/2 full is above the on engine filters and above the lift pump.

When the bleed screw on top in final filter assembly is opened, fuel never ever flows out unless hand priming the the lift pump lever. This suggests that fuel cannot "leak" past the lift pump or defective injector when fuel tank level higher than injection pump.

In the 555 case it should be easy enough to check the shut down engine for gravity based fuel flow past the on engine filter and before the lift pump. In other words, could the engine be self priming?

Also Seafever, do you have an electric fuel pump feeding the engine?

sunchaser said:

In the 555 case it should be easy enough to check the shut down engine for gravity based fuel flow past the on engine filter and before the lift pump ( insert - injection pump ). In other words, could the engine be self priming ?

Click to expand...

In above post #36 I meant to say injection pump as shown

C lectric said:

I'll take a bit of a stab.

The PT pump supplies fuel to the cylinder heads in a gallery common the all injectors. It is pressurized to several hundreds of pounds but varying depending upon engine speed. When the injector is actuated there is valving internal to the injector which isolates the the injector from the gallery and then pressurizes the fuel as it injects up to ~ 20,000psi. At a certain point another valve function bleeds excess fuel back to the return line.

Unlike the more common injector pump the real pressure is developed at the injector from the camshaft.



Paul Foulston had a name for the action, which I cannot remember, but it was fast, abrupt and effective.



I have read the operation but it was a long enough time ago now I don't remember all the details.

Click to expand...

This is my understanding too. But I've additionally always understood that as part of all these systems, the actual nozzle tip is essentially a pressure relief valve that only sprays when the fuel is under high pressure. One of the checks of an injector nozzle is the drip rate which is the leak-by rate.

Sunchaser,

YEs they are. Unlike many if you get the fuel close to the PT pump the engine, when cranked, will start without the usual priming or undoing of injectors. These systems will clear the air of the lines.
Typically I use a small electric pump to fill my BIG filter and then crank the engine. It will finish the job on its own which is what I used to do.
I finally used a modified method to ease that process on the starter but yes the engines will self prime.

C lectric said:

Sunchaser,

YEs they are. Unlike many if you get the fuel close to the PT pump the engine, when cranked, will start without the usual priming or undoing of injectors. These systems will clear the air of the lines.
Typically I use a small electric pump to fill my BIG filter and then crank the engine. It will finish the job on its own which is what I used to do.
I finally used a modified method to ease that process on the starter but yes the engines will self prime.

Click to expand...

C lectric

Is it possible that for whatever reason an electric fuel pump was activated (or not shut down) and fuel flooded the engine? Which is why I asked if the engine in question has an electric fuel pump.

Good thought.

If an electric pump was used and not shut down it definitely could .

I just dug out my PT fuel system shop manual and looked in the complaints list.

According to the Cummins manual, it is for trucks, there are two ways of this happening and both require a fuel level to be above the injectors.

FLOODED CYLINDERS can be caused by fuel levels above the injectors.
In the case of trucks by parking so the tank outlet is above the engine or if the tank is mounted in a manner that puts it above the engine.

The book suggests one method that should work to prevent that and that is a float chamber so a rising level in the chamber would raise a needle valve to close the line much like a carburettor.

So for Capt. Sea Fever this could happen again. His boat must have something odd with the installation and maybe combined with some other quirk it could happen again.

Ensuring the tank outlets fuel supply valves are closed, ensuring the return line check valve is working properly, the float chamber or as suggested an electric shutoff valve between the tanks and the PT pump that is energized/de-energized with the PT shutdown valve so there is double protection.

I looked at my own boat and in my case the tank fuel level would never be above the PT pump/engine.

I suggest to Capt. Sea Fever that he examine his system carefully, ensure the shutdown valve has new seals, check the checkvalve and replace it, figure out a system of ensuring the tank outlet valves are closed with a sign put over the starting positions, ensure the tank vent hoses are clear and not obstructed in any way. That includes any dips that can hold fuel. Dips can act like a P trap and cause trouble. Ideally the hose should be a constant rise from the tank to the hull fitting actually to a point somewhat above the hull fitting and then down to prevent seawater splashes entering the tank.

It also sounds like it cannot happen overnight but if there is a fault in the check and shutdown valves then who knows.

twistedtree said:

This is my understanding too. But I've additionally always understood that as part of all these systems, the actual nozzle tip is essentially a pressure relief valve that only sprays when the fuel is under high pressure. One of the checks of an injector nozzle is the drip rate which is the leak-by rate.

Click to expand...

I thought so too. Looks like not unknown in the truck world but I'd never heard of it in the marine world although not a mechanic.

Evidently there is a quirk that can allow flooding of cylinders under the right[wrong] circumstances. It may also need a worn shutdown valve or , I'm guessing here, a worn return line check valve.
Or/and a worn or sticky injector.

tidbits from a marine engineer with personal experience on these engines....

"A couple of guys are getting it. The injectors on the PT system operate backwards from most styles in that the nozzle is always open to the cylinder. Most injectors close the nozzle with the plunger "needle" and the sac or space between the needle and the nozzle holes is as small as possible. Modern systems try to eliminate the possibility of fuel in the sac in order to reduce emissions and prevent nozzle clogging with carbon. The OP's Cummins fills the sac as a way to meter the amount of fuel injected and the cam pushes the needle down to pressurize the fuel for injection. It does not make for a clean crisp start of injection like a pressure lift style valve, fuel begins to flow as soon as sac pressure is greater than cylinder pressure. This means for the start of injection the fuel is more of a drip or stream than an atomize mist.
The open sac also means that a worn injector with the cam stopped in the "wrong" spot could allow fuel from the rail to drip into the cylinder. In order to hydrolock the engine though it would have to either go for a very long time or have multiple injectors and fuel pump parts worn out way past replacement time. The oil level would have been extremely high ... the OP said that there was plenty of oil, it sounds like he didn't know what the level should have been. The dipstick on the VT555M is high above sump so unlike other engines it would not overflow but it would certainly be at cylinder level on the stick and obvious to anyone who looked at it. The only way a cylinder would hydrolock is after the oil level was at the top of the cylinders so that there was no way for the dripping fuel to drain to the sump.

We had those engines on our boat in Oxford so know them fairly well."

psneeld said:

tidbits from a marine engineer with personal experience on these engines....



"A couple of guys are getting it. The injectors on the PT system operate backwards from most styles in that the nozzle is always open to the cylinder. Most injectors close the nozzle with the plunger "needle" and the sac or space between the needle and the nozzle holes is as small as possible. Modern systems try to eliminate the possibility of fuel in the sac in order to reduce emissions and prevent nozzle clogging with carbon. The OP's Cummins fills the sac as a way to meter the amount of fuel injected and the cam pushes the needle down to pressurize the fuel for injection. It does not make for a clean crisp start of injection like a pressure lift style valve, fuel begins to flow as soon as sac pressure is greater than cylinder pressure. This means for the start of injection the fuel is more of a drip or stream than an atomize mist.

The open sac also means that a worn injector with the cam stopped in the "wrong" spot could allow fuel from the rail to drip into the cylinder. In order to hydrolock the engine though it would have to either go for a very long time or have multiple injectors and fuel pump parts worn out way past replacement time. The oil level would have been extremely high ... the OP said that there was plenty of oil, it sounds like he didn't know what the level should have been. The dipstick on the VT555M is high above sump so unlike other engines it would not overflow but it would certainly be at cylinder level on the stick and obvious to anyone who looked at it. The only way a cylinder would hydrolock is after the oil level was at the top of the cylinders so that there was no way for the dripping fuel to drain to the sump.



We had those engines on our boat in Oxford so know them fairly well."

Click to expand...

Very informative, and good clarification of my previous understanding. But it sure would be nice if people could post directly rather than through surrogates.

Technically, the position of the "rack" (attached to the power lever) determines how far the cam lobe can/will push the injector...which establishes the amount of fuel injected. Simple and effective designs, especially for a boat where the injector rack sees very little movement (wear), as opposed to a truck application where the rack is constantly moving with the accelerator pedal.

twistedtree said:

Very informative, and good clarification of my previous understanding. But it sure would be nice if people could post directly rather than through surrogates.

Click to expand...

Sometimes surrogates are required for those who aren't in favor with TF mods.

Sea Fever
Are your tanks higher than the PT system? If no, this thread will require a turn to port.

A little more info....

"Here's another correction.

The 555 does not have a "rack." The amount of fuel injected is determined by fuel pressure and the time available to fill the "cup" or injector sac. The distance "pushed" or stroke of the injector is the same at idle as it is a full power. The comment quoted is totally false and only confuses the issue further."

psneeld said:

A little more info....

"Here's another correction.

The 555 does not have a "rack." The amount of fuel injected is determined by fuel pressure and the time available to fill the "cup" or injector sac. The distance "pushed" or stroke of the injector is the same at idle as it is a full power. The comment quoted is totally false and only confuses the issue further."

Click to expand...

I stand corrected. Was thinking Detroit. This link provides a decent description of the Cummins PT fuel system/design: http://www.liberatedmanuals.com/TM-55-4018-1.pdf

and more from a marine engine expert....

" Fuel delivery quantity on a DD injector is determined by the closing point of the spill port which is determined by the rack position. The length of a plunger stroke is constant regardless of load and is determined by the cam profile. "

psneeld said:

and more from a marine engine expert....

" Fuel delivery quantity on a DD injector is determined by the closing point of the spill port which is determined by the rack position. The length of a plunger stroke is constant regardless of load and is determined by the cam profile. "

Click to expand...

That is correct. By the way, the marine engine expert confuses the issue in the earlier descriptive post by characterizing the plunger in the Cummins injector as the needle. The pumping operation of this type of injector requires correct terminology for clarity. See the description of the injector design and operation in reference document I posted earlier.

An UPDATE...
All of the injectors were cleaned and the injector pump rebuilt. Much water was found in the pump.
I installed new glasses in my Racors.
The engines are working fine.
Every half hour though I have to empty approximately a cup of water from the SB Racor...not the P Racor.
Since the SB engine repair last week I have discovered that the SB fuel tank hasn’t budged. All of the fuel for the SB engine is coming from the P tank despite the fact that the fuel tank valve on the SB side is opened during use.
My question....why is all the water accumulating in the SB Racor and none in the P Racor?
Also, I suspect that the SB fuel line is plugged.
Thoughts please?
Thanks

Yes, check your fuel lines. Maybe you can blow them out? Do you have a sump/drain on your tanks? Could your tank vent be taking on seawater - perhaps the opening is angled forward? I would drain the stbd tank completely also, to be certain you have all the water out of it. If you have inspection ports, then clean any gunk from the bottom of the tank as well.

Maybe your fuel returns are unbalanced? The 555's do have a high return fuel flow, but it would be quite a coincidence that the return to Stbd would balance the draw, so a pinched or blocked line is more likely.

VT555M Manual

Hi there, I am looking for this engine manual but the only option I found was to pay for it. Is there someone who could kindly share it?

I would appreciate that.

Thanks in advance.

Send me a dm with an email address and I can probably send you a link to some stuff.

Thanks! I just did it.

Responded!

I too have diesel in the sump oil.
I was running the engine in the marina and noticed a decent slick coming out of the wet exhaust.
How the oil looks very thin.
Can’t see any fuel coming out of the PT pump weep hole so I’m thinking maybe an injector ?
The engine only has about 5 hours on it since it was rebuilt by Cummins.
How ever that was about 15 years ago.

Diesel in oil comes from some point diesel and sump oil meet.
This is usually the injector pump seal leaking into the crank case. But it can be mechanical lift pump has a hole in the diaphragm. Or a blown head gasket, or a crack in the block or head.

HP pump shaft seals can be a source of diesel in the oil sump.