Ensure the Reliable Operation of your Generator Set with Proper Coolant and Cooling System Maintenance

Certain types of coolant may adversely affect the functionality of Northern Lights generator sets. The Northern Lights Service Department offers the following troubleshooting tips:

  • Straight water with additive is not recommended on Northern Lights generator sets as they may cause damage to the engine.
  • Some brands of Hybrid or OAT type coolants have been reported to cause the OEM thermostat to stick, leading to overheating. In addition, some extended life coolants have been found to cause leaks in the generator set’s pump seal. In such conditions, flush the coolant system thoroughly and refill with an approved Northern Lights coolant.
  • All engines with wet liners require a supplemental coolant additive (SCA) to prevent liner erosion and pitting in the circulating water pump impeller. Northern Lights recommends heavy duty diesel rated coolants, which include an SCA. If a heavy duty diesel rated coolant is not available, add an SCA to prevent the symptoms noted above.
  • It is the responsibility of the customer to understand that the use of incompatible coolant may cause damage, so please help educate them.

For use in Northern Lights generator sets, the following coolant types are approved:

  • Conventional Propylene Glycol based coolants.
  • Conventional Ethylene Glycol based coolants.

Please refer to your operators’ manual for your specific unit’s coolant requirements and specifications.
Should you encounter of the above conditions, or have additional questions about Northern Lights coolant recommendations, contact your Factory Service Representative.

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Northern Lights Training Course Catalog

Northern Lights, Inc. is dedicated to manufacturing the industry’s best marine products. As part of our commitment, we offer training courses to our dealers, clients and captains to ensure that the world’s best built marine generator sets are the best maintained and serviced as well.

Contact your nearest Northern Lights branch location to sign up for any of these classes, or for more information. Together, we offer clean power and complete solutions.

Download the training course catalog

Proper Loading of Marine Diesel Generator Sets

Among the most common issues people report with their marine generator sets are dirty exhaust or “wet stacking”. Most frequently, this condition is caused by cylinder glazing and carbon build-up. The root cause is simple: underloading the genset.

 

Diesel engines in marine gensets should typically run at least 60-75% of their maximum rated load. Short periods of low load running are permissible providing the set is brought up to full load, or close to full load on a regular basis.

 

Running a diesel engine under low load conditions causes low cylinder pressures, and consequent poor piston ring sealing. The ring-to-liner seal relies on combustion gas pressure to force the piston rings against the oil film on the cylinder bore. Low cylinder pressures result in low temperatures and poor combustion, leading to soot formation and unburned fuel residues and ultimately clogging of the ring grooves. Advanced cases of this condition can even cause the rings to stick in the grooves, further damaging the cylinder bore.

 

Cylinder glazing occurs when hot combustion gases blow past the now poorly sealing piston rings, causing the lubricating oil on the cylinder walls to flash burn, creating an enamel-like glaze. This smooths the bore and minimizes the effect of the honing marks machined into the bore surface.

 

Hard carbon is highly abrasive, and is also formed from poor combustion. It wears the honing marks on the bores, leading to increased oil consumption, evidenced by blue smoke. Poor combustion also clogs injector tips, resulting in black exhaust smoke.

 

The problem is further exacerbated by the formation of acids in the engine oil from condensed water and combustion by-products which would normally boil off at higher temperatures. Acidic buildup in the lubricating oil causes damaging wear to bearing surfaces.

 

Running your generator set lightly loaded will inevitably shorten the service life of the engine, and results in pollution that is unacceptable to you, to port authorities and to neighboring vessels. Prevent costly repairs and downtime by maintaining adequate engine load on your genset.

 

If you encounter any of the above problems, or just want more information, contact your nearest Caribbean dealer, visit wwwCaribbeanNorthernLights.com or call Parts and Power at 284-494-2830

Proper Loading of Marine Diesel Generator Sets

Among the most common issues people report with their marine generator sets are dirty exhaust or “wet stacking”. Most frequently, this condition is caused by cylinder glazing and carbon build-up. The root cause is simple: underloading the genset.

Diesel engines in marine gensets should typically run at least 60-75% of their maximum rated load. Short periods of low load running are permissible providing the set is brought up to full load, or close to full load on a regular basis.

Running a diesel engine under low load conditions causes low cylinder pressures, and consequent poor piston ring sealing. The ring-to-liner seal relies on combustion gas pressure to force the piston rings against the oil film on the cylinder bore. Low cylinder pressures result in low temperatures and poor combustion, leading to soot formation and unburned fuel residues and ultimately clogging of the ring grooves. Advanced cases of this condition can even cause the rings to stick in the grooves, further damaging the cylinder bore.

Cylinder glazing occurs when hot combustion gases blow past the now poorly sealing piston rings, causing the lubricating oil on the cylinder walls to flash burn, creating an enamel-like glaze. This smooths the bore and minimizes the effect of the honing marks machined into the bore surface.

Hard carbon is highly abrasive, and is also formed from poor combustion. It wears the honing marks on the bores, leading to increased oil consumption, evidenced by blue smoke. Poor combustion also clogs injector tips, resulting in black exhaust smoke.

The problem is further exacerbated by the formation of acids in the engine oil from condensed water and combustion by-products which would normally boil off at higher temperatures. Acidic buildup in the lubricating oil causes damaging wear to bearing surfaces.

Running your generator set lightly loaded will inevitably shorten the service life of the engine, and results in pollution that is unacceptable to you, to port authorities and to neighboring vessels. Prevent costly repairs and downtime by maintaining adequate engine load on your genset.

If you encounter any of the above problems, or just want more information, contact your nearest Caribbean dealer, visit wwwCaribbeanNorthernLights.com or call Parts and Power at 284-494-2830.

Northern Lights Visits Customers at Antigua Charter Yacht Meeting December 2015

From 5-9 December members from the Northern Lights family visited customers at the 54th Annual Antigua Charter Yacht Meeting (ACYM).

The Charter Yacht Show was very successful with 105 yachts ranging in size from 62 ft to 296 ft. In addition there were another 40-50 yachts in Falmouth Harbour which were not in the Show.

Mike Prado and Nils Nelson, from Deerfield Beach, Vice President/General Manager, Brian Vesely, from Seattle, and Tom Gerker from NL Distributor Parts & Power visited vessels on Falmouth Harbour Marina, the Yacht Club Marina, the Dockyard Marina and the Catamaran Marina.

They found many of the yachts had Northern Lights products on them, both generators and Lugger propulsion engines. In most cases they received nothing but favorable reports from Engineers and Captains. A few vessels had questions or problems on their equipment that the team was able to address. In many cases the NL representatives found a recurring theme that they had discovered at previous shows. Many of the NL customers simply needed advice on how to maintain their Northern Lights equipment, and where to go to get information. In some cases, issues that Engineers and Customers were having in the field were recorded by Brian so he could make changes in Production at the Factory to make Northern Lights products even better.

They found that, in some cases, customers were overhauling their generators prematurely. Because they had owned competitor’s products in the past who recommended overhauls at 10, 15 or 20,000 hours, they felt that they had to do the same on their NL product. Several customers had done overhauls or repairs at 10 or 15,000 hours to find so little wear that they questioned the value in having done the work. Brian and Tom recommended using oil analysis and valve adjustment measurements to monitor wear, as many Northern Lights generators run well past 30,000 hours with nothing but routine maintenance.

Northern Lights were, once again this year, the only engine or generator manufacturer who attended the show. They have been attending the Show for over 15 years, to meet their customers and get feedback on the performance of their equipment. Customers who attend the ACYM typically own generators that run for extensive periods of time, and are more often than not in distant locations far away from a repair facility. So their generators must run reliably.

Having the new General Manager at the show allowed Brian to hear the Voice of the Customer in order to make changes and improvements to the current product, and get an idea of what customers were looking for in future products.

NL M1066A1 generator on board MY Odessa
NL M1066A1 generator on board MY Odessa
Vice President/General Manager, Brian Vesley, with Chief Engineer Dan O’Rourke
Vice President/General Manager, Brian Vesley, with Chief Engineer Dan O’Rourke
SY Marine with 2 x NL M1064A generators on board
SY Marine with 2 x NL M1064A generators on board
Various yachts at the show
Various yachts at the show
Various yachts at the show
Various yachts at the show

SUMMER TIME IS ANNUAL MAINTENANCE TIME FOR YOUR NORTHERN LIGHTS GENERATOR

Summer time is the off season for many in the Caribbean, whether you are a cruiser sitting out Hurricane Season or a Charter vessel taking a well-deserved break.  Before you put the boat up on the hard, or leave it at the dock for the summer, do your diesel engines a favor.  Before you leave your hard working Northern Lights generator for the summer, be sure to change the oil.  The oil is the life blood of your engine.  It holds all the dirt, acids, soot and by products of combustion in suspension.  That contaminated oil sits on all the surfaces serviced by your oil and expedite corrosion if left for prolonged periods.  In addition, oil oxides when left exposed to the air, reducing its effectiveness at lubricating your engine and holding contaminants.

So do your engine a favor and change the oil before you put it in storage.  While you’re at it, why not do your Annual Maintenance?

Annual Maintenance?  What is Annual Maintenance?

If you look at your Operator’s Manual, you will notice a section that says “Every 12 Months”.  Everything in there is due every year.  Generally this includes: Oil Change, Valve Adjustment, Air Filter replacement, Fuel filter replacement and Injector Testing.  Check your manual to see if there is anything else included, but the above are fairly common with most diesel engines and Northern Lights generators.

We discussed the oil change.  Even if you don’t have the 200 or 250 hours dictated by the oil change interval, remember that oil oxidizes even if not being used.  So changing oil makes sense, but why check the valves?  Besides making sure that your engine is “breathing” properly in terms or air in and exhaust gases out, it also can pick up signs or engine wear.  If the valve clearances are narrow, that can mean that the valve in question is wearing the valve seat.  This may be a sign that your engine is getting ready for a top end overhaul.  If caught early, this is fairly routine.  If caught too late, the repair could be far more costly.  You could be looking at a new cylinder head, or a “dropped valve” which can be catastrophic.

You might think that, because your engine is clean, you don’t need to change your air filter.  Many Northern Lights generators have foam air filters which, not only filter the air, but aid in noise dampening.  These filters deteriorate with heat and over time.  If not changed, they will start to turn into powder and fall apart.  The foam will not hurt the engine but we have seen cases where large pieces of the air filter were sucked into the intake valves. In such a case, the engine loses compression (because the intake valve will not close completely) and will not start or run.  This is not only difficult to troubleshoot, but requires the removal of the cylinder head.  So the $20 spent on a new air filter is a very good and wise investment.

Not everyone checks injectors every year.  If you are not putting a lot of hours on the generator, it starts quickly and is running clean, you might be able to skip this.  But the service interval on injectors can be as low as every 700 hours (or once per year).  In addition, an injector nozzle that is “squirting” rather than “spraying” can melt a piston in a very short period of time.  So if you have a shop that can test the injectors, the process can offer great peace of mind.

Take the time to review your Operator’s Manual or discuss its maintenance with your local dealer.  Your generator was an expensive investment.  If given reasonable maintenance and operated properly, your Northern Lights generator should give 20,000 hours of operation or more.  But we’ve seen improperly maintained units struggle to provide half that life.  Doing your Annual Maintenance is a good way of assuring that your generator will give you the reliable life expectancy Northern Lights customers have come to expect from their product.

Noise reduction for Generators

sound_enclosure1

 

When I set out to write this blog piece I thought it would be a simple matter of writing about sound enclosures, construction materials and noise reduction. However, when I started researching these areas I quickly realized there is too much material for a single blog to be meaningful. This is therefore the first in a series of blogs on the topic of noise reduction for generators.

Part 1 – Noise

With the continued and expanding use of diesel generator sets there has come an increased focus on controlling the noise these generators create. Whether generator sets are located in enclosures outside a facility or home, inside, on the roof or even on a yacht, designers are making more efforts to control generator set noise and vibration in order to reduce the effects on neighbours and building occupants alike. Whether generator sets run continuously in prime-power applications, intermittently in demand response applications, or occasionally in emergency standby situations or testing, their operating sound levels nearly always require remediation due to market requirements.

In order to understand the solutions to reducing noise from generators, it is first necessary to understand noise. Therefore this blog provides a simple summary of noise and its characteristics, and the sources of noise created by generators.

What is Noise?

 

Vibrating objects induce pressure waves that travel through the air, reaching our ears as sound. Noise, by definition, is simply undesirable sound. When the amplitude of the pressure waves becomes too high, the amount of sound becomes uncomfortable. In addition to being annoying, excessive sound can cause permanent hearing damage. The following diagram explains the physiology of what happens when sound reaches the human ear.

 

fig22

 

 

The human ear has such a wide dynamic range that the logarithmic decibel scale (dB) was devised to express sound levels in a convenient way. The ratio between the softest sound the ear can hear and the loudest sound it can experience without damage is approximately a million to one. By using a base-10 logarithmic scale, the whole range of human hearing can be described by a more convenient number that ranges from 0 dB (threshold of normal hearing) to 140 dB (the threshold of pain).

chart

There are two dB scales used to describe sound: A and L.

  • The dB(L) scale is linear and treats all audible frequencies as having equal value. However, the human ear does not experience all frequencies the same way. Our ears are particularly sensitive to frequencies in the range of 1,000 to 4,000 Hz, and they are less sensitive to sounds in lower or higher frequencies. (This is why dogs often start barking for reasons humans don’t understand – dogs have the ability to hear sounds of a much higher frequency than humans)
  • To adjust the sound pressure levels to more accurately reflect what the human ear perceives, the frequency-weighted dB(A) scale has been adopted as the official regulated sound level unit.

It is also worth noting that the db(A) scale represents an “absolute” value. For example, stating that a generator produces 98 db(A) of noise isn’t particularly meaningful – remember by definition it can only be noise if it is undesirable to the recipient. Standing alongside a generator generating 98 db(A) of noise is completely different to standing 500 meters away (where it probably couldn’t be heard).

More useful therefore is to state at what distance from the generator the noise level is experienced. As a result most generator manufacturers state sound levels in terms of db(A) @ x meters, for example 85 db(A) at 1 meter. This in turn presents challenges in terms of measurement, but that is a topic for a later blog.

Sound produced by generator sets

The principal sources of noise from generators are described below.

1 Engine mechanical noise

With the advent of high-pressure common rail fuel injection, advanced turbocharging and better combustion control, manufacturers have significantly reduced overall mechanical noise from diesel engines. The amount of sound varies with the size of the engine and its load, and can be as high as 110 dB(A) measured at one meter. Engines with more cylinders have more power strokes per revolution and therefore deliver a smoother flow of power with less vibration. Smaller engines tend to be harsher in operation and produce more noise and vibration for their size.

2 Exhaust noise

Engine exhaust is a major contributor to overall sound levels. When measured without an exhaust silencer noise can be 120 dB(A) or more depending on the size of the engine. The sound level can be reduced by up to 40 dB(A) depending on the silencer employed.

3 Cooling fan noise

Sound emanates from turbulent air as the cooling fan moves air across the engine and through the radiator. The amount of sound varies with the speed and volume of air being moved as well as with the design and distortion of the fan blades. The amount of sound can be as high as 95 dB(A) at one meter.

4 Alternator noise

The alternator has an internal cooling fan, and the combination of cooling air movement and brush friction produces noise. However, the sound level is always small compared to the driving engine.

5 Induction noise

Current fluctuations in the alternator windings create mechanical noises that add to total noise when load demand changes.

6 Structural/mechanical noise

This is caused by mechanical vibration of various structural parts and components that is radiated as sound. Isolators between the engine, alternator, controls and other components help to reduce the amount of vibration that gets converted to noise. Anti-vibration mounts can also be employed to reduce noise propagation through the ground or hull where the generator is located.

Summary

In this first blog we have introduced the definition of noise, described its impact on human beings and highlighted the sources of noise from generators. In the next blog we will discuss methods for attenuating these noise levels.

 

Images courtesy of http://conocimientosamplifiersfr.blogspot.com.

NORTHERN LIGHTS 5-20 KW HEAT EXCHANGERS

I was helping a customer the other day who requested a heat exchanger tube stack for an M753K.  This is a 10 year old generator, but I was still shocked that he needed a heat exchanger.  In our experience, the only thing that can cause a heat exchanger tube stack failure on a 5-20 kw generator is very poor maintenance.  When I looked up the part number for the tube stack I noticed that we had sold 3 in the last 12 months.

There are, conservatively 300-400 of these generators in operation in the Caribbean, so that works out to less than a 0.75% failure rate.  Most of our competitors would be envious of such a low failure rate, but we still feel that is too high.  The only reason that these tube stacks are failing is because of poor maintenance practices, or using the wrong coolant.

We need to educate our customers that the only proper coolant is Distilled Water, or a 50/50 premix ethylene glycol mix.  If our customers want to use 100% ethylene glycol, they need to dilute it with 50% Distilled Water.  Most of the water we get in the Caribbean comes from Reverse Osmosis, and that often leaves too high a mineral (including salt) content.  Even with proper coolant, sludge, scale and corrosion build up over a period of time.  So we recommend that our customers drain, flush and refill their cooling system every year as part of their annual maintenance.

If the customer wants to extend the coolant change interval, they should purchase a pack of coolant test strips (part number 20-00005) and test their coolant every 6 months past the 1 year anniversary of the last coolant change.  The coolant strips cost $15.  A tube stack costs nearly $500.

In addition to the tube stack failing, poor coolant quality can cause water pump failure, and the core plugs (water jackets) to corrode from the inside out.  Made of a thinner, less corrosion resistant material, the core plugs can often be the “canary in the coal mine”.  If they start to leak, the customer knows he has a problem.  A bigger problem is that some of these core plugs can be very hard to get to in order to change them.

So we need to emphasize to our customers that it is a very good investment to change their coolant every year, even if they need to hire their local dealer to do so.  It can save them a lot of money down the road.

 

THE GOOD AND BAD NEWS ABOUT EMISSIONS REGULATIONS AND THEIR IMPACT ON NORTHERN LIGHTS MARINE GENERATORS

If you mention the words “emissions regulations” to anyone in the diesel engine industry, you will usually detect a noticeable cringing on their part.  It is followed by bad news that is sometimes downright distressing.  Yet the news is not all bad.
As far as the effect of EPA Emissions Regulations on Northern Lights Marine Generators the good news is that the product line under 40 kWw, which constitutes the majority of the product in the Caribbean, remains largely unchanged (IMO has no regulations for engines below 175 hp).  The M673LD3 (5 kW @ 60 Hz) through the M844LW3 will not see any changes for the foreseeable future.  The M944T will be changed to the M944T3.  The only outwardly apparent difference will be a rating change from 38 kW to 40 kw in 3 phase configurations, but the 1 phase rating will remain at 38kW.
The 30 kW (M944W3) is an unfortunate victim of the tightened emissions threshold. The engine cannot achieve emissions regulations at 60 Hz, but the 50 Hz version at 26 kW remains a viable and available product for appropriate applications.  The 25kW-40kW rating gap (at 60Hz) is recognized as being a significant hurdle, and Northern Lights’ product development team is actively seeking alternatives to close this gap and fill out the product line.
Above 40 kW, the news remains largely good for any vessel under 500 gross tons as the Northern Lights product line meets emissions standards without after treatment.  Beginning in 2016, vessels above 500 gross tons will need after treatment (in the form of SCR: Selective Catalytic Reduction) to achieve the NOX levels set by the IMO.  Thankfully, most of us dodge the after treatment bullet until the regulations again change in 2021 for sub-500gt vessels.  After that, any vessel with an engine producing 127 kW or greater will be required to have after treatment for NOX.  However, Northern Lights will continue to stay ahead of the emissions technology curve and is already working to provide a fully-compliant package for the upcoming regulations around the world.
Interestingly IMO is not addressing “soot”, the bane of most marine diesel engine owners.  Despite that, Northern Lights has been addressing soot for many years.  Some may remember the old STARS units (Soot Trap And Regeneration System).  It was very effective for treating soot in exhaust.  It used heaters that doubled as a load bank and also heated the exhaust gas to a level where it could be catalyzed.  Due to problems, mostly dealing with misapplication and maintenance, the product line was discontinued some years ago.  Today’s solution is called a Diesel Particulate Filter (DPF) that does not need heaters.  The DPF does need to be closely matched to the engine though to make sure that the generator Exhaust Gas Temperature (EGT) is high enough to be properly catalyzed. With the benefit of less complicated systems to clean our exhaust, comes the burden to periodically clean the catalytic “brick”.  More maintenance! However, the fact that DPF technology has been widely adopted in both on-highway and industrial applications means that there are a number of outlets for DPF filter cleaning in most ports of call around the world.
So, it could be worse, as they say. Most of us can continue to use our generators in the manner that we have been accustomed to, due to some engineering magic done by Northern Lights.  But changes will be felt by the larger yacht owner and crew.  Years of experience has taught us that as soon as we learn to comply with the new regulations, there will be more on the horizon.  However, the progressive team at Northern Lights will continually strive to keep us ahead of the regulatory curve, no matter what new challenges come our way!

DIESEL ENGINES ARE SIMPLE

A little over a year ago I had spinal surgery.  It was not something I wanted to do and, indeed, did everything I could to avoid it.  In the process, I saw 13 different health professionals.  Of those 13, only 2 agreed on what was wrong and what action to take.  They were both wrong.  Of the other 11, not only did they disagree with the other 10 opinions, but they said that the previous advice was the worst thing I could possibly do.

This gave me a greater appreciation of what I’ve devoted the last 35 years in dealing with: diesel engines.  Although there are a variety of opinions on diagnosis and treatment of diesel maladies, they should not differ that much.

Unlike the human body, diesel engines are very simple devices.  All they need is Air, Compression and Fuel.  If they have that, they will run.  They may not run all that well, but they will run.  Getting them to run well may take a bit of finesse, but they will run.

The principles of diesel engine operation was best described to me as Suck, Squeeze, Bang, Blow.  This applies to 4 stroke diesel engines, of which the vast majority of modern diesels are.  The first down stroke happens with the Intake Valve open.  This “sucks” in air.  As the piston starts its second stroke upward the intake valve closes.  This causes the air to compress or “squeeze”.  At or near Top Dead Center, fuel in injected.  The atomized fuel hitting the hot compressed air causes it to ignite or “bang”.  This causes the third stroke downward, or the “power stroke”.  On the upward 4th stroke, the exhaust valve opens and the ignition residue, or “exhaust” is “blown” out, completing the 4 cycles of a diesel engine.

Take one of the 3 elements required away, and the engine will not run.  So let’s review them in order of simplicity to identify.  
Fuel.  To determine if there is fuel, you can loosen the high pressure pipes at the injectors.  You don’t want to completely disconnect it, and you certainly don’t want to get body parts or anything you want to hang onto into the potential spray pattern.  Injection pressures can exceed 20,000 psi on some engines.  By loosening the connectors though, you should be able to see if fuel is coming out.  If there is no fuel, you need to work your way backwards to see where the fuel is being interrupted.  A shortcut to this sometimes tedious process is to determine if it is a “boat” problem, or an “engine” problem.  This can be done by gravity feeding fuel to the low pressure fuel pump.  A simple way is to disconnect the fuel inlet and return lines.  Run both into a gallon jug of known good, clean diesel.  Bleed the air out of the system per the manufacturer’s instructions, then try to start the engine.  If the engine starts, you have a “boat” problem.  If the engine doesn’t start, then you have an “engine” problem.  Now you can troubleshoot with a narrower focus.

Air is the next easiest to determine.  Air not only includes air going into the engine, but exhaust “air” leaving the engine.  So you need to check it from Appetite to Ass…er, Exhaust.  Air In is pretty easy.  If restricted, you usually get warning signals such as black exhaust.  Intake air problems can include a dirty air filter or a plugged after cooler.  Start from the beginning and check everything until you can look inside the intake ports on the head.  If there is nothing in the way, then it is not Air In.  Air Out is more problematic.  We have seen everything from plugged exhausts to collapsed inner liners of the exhaust hose.  We once had a customer who rebuilt his engine three times before he finally looked at his exhaust elbow.  It was plugged with carbon, and its 2” port had narrowed to about ¼”.  Again, start at the beginning and work your way to the end.  It is very common to find the exhaust outlet plugged at the water injection point on the exhaust elbow.  This is especially true of lightly loaded diesels.  Extensive running of a diesel engine to only charge batteries or run a refrigeration compressor spell early death for a diesel engine.

If both Fuel and Air is present, then it only leaves compression.  Compression can only be measured using a “compression tester”.  It requires a gauge, a hose and an adaptor to connect the hose to the cylinder.  A “cannibalized” injector is the most common adaptor.  If you don’t have compression tester, you will need to hire someone who does.

There are no “set” numbers for compression.  The number depends on a lot of variables, including atmospheric conditions (temperature, humidity, and barometric pressure), battery voltage, the volume of space inside the test equipment, and a few other factors.  Diesel engines that have low compression almost never have identical wear on all cylinders.  One cylinder will “fail” first.  It might be a burned or corroded valve, a broken ring, bore wear, bore glazing, or a variety of other problems.  But one, or maybe two, cylinders will fail before the others.  So, when a compression test is done, the examiner is looking for differences in compression between cylinders.  If they are all very close (within 50-60 psi), compression is good.  If all are reading on the low side, a commonly used technique is to squirt oil into the cylinder and do a second test.  If the compression comes up significantly, the problem tends to be rings.  If the compression does not, the problem is most likely valves or, more precisely, the failure of the valves to seat tightly in the head.

So, unlike the human body, diesel engines are pretty straightforward.  If you are getting a lot of different diagnoses and treatment suggestions, you are talking to a lot of the wrong people.  It’s time to seek out someone who has been trained and has experience with your particular engine.   If you can find 2 such people, then get your second opinion.  They ought to be pretty close.  Hopefully they won’t tell you that, what the other guy said, was the worst possible thing you could do.