DN2M / DN4M engine experts, a Q about stuck rings.

[Digger556]

My first generator was a 802a I snagged off CL for $800. It's older, a 1994 model, but low hours (221 hrs) and decent shape for its age.

However, its always been slightly down on power and based on cold start, full load performance, blowby, etc, I would guess it's lost some compression. My first thought was stuck rings, but I was curious if there was an outward of determining stuck rings from broken rings?

Honestly, it's probably fine being a backup unit, but it would be great to get it in top running condition.

 

[Scoobyshep]

My first generator was a 802a I snagged off CL for $800. It's older, a 1994 model, but low hours (221 hrs) and decent shape for its age.

However, its always been slightly down on power and based on cold start, full load performance, blowby, etc, I would guess it's lost some compression. My first thought was stuck rings, but I was curious if there was an outward of determining stuck rings from broken rings?

Honestly, it's probably fine being a backup unit, but it would be great to get it in top running condition.

Stuck rings typically can unstick and improve, that's about the only difference I can think of

 

[Digger556]

Stuck rings typically can unstick and improve, that's about the only difference I can think of

That's what I'm hoping to get out of this. It's not bad enough to tear the engine down.

Would stuck rings burn more oil or have lower compression than a broken ring? (given other conditions remain the same)

One other bit of information, when a large load is applied, the engine smokes a lot (black), but slowly subsides as the heat builds. I've been assuming this is because the piston is expanding and closing the gap not covered well by the rings.

 

[98G]

That's what I'm hoping to get out of this. It's not bad enough to tear the engine down.

Would stuck rings burn more oil or have lower compression than a broken ring? (given other conditions remain the same)

One other bit of information, when a large load is applied, the engine smokes a lot (black), but slowly subsides as the heat builds. I've been assuming this is because the piston is expanding and closing the gap not covered well by the rings.

What's the longest you've ran it above 75% load?

 

[Digger556]

1-2 hours at a time, every 1-2 months.

 

[98G]

Any signs of wetstacking?

 

[Digger556]

No signs, exhaust is dry with soot similar to my 3 other units.

 

[Ray70]

Do you get any light colored smoke for the first 30-60 seconds at cold start?
Or just the normal quick 2 second puff of black at start up while the governor adjusts itself?
If it smokes a little light gray/blue for 30-60 seconds, that's another indication of stuck rings = lowered compression.
You can also put a small piece of paper over the oil fill cap opening while running. A normal engine will tend to pull the paper against the opening while stuck rings will blow it away from the opening.
I know a couple guys who swear by Hot Shots stiction eliminator added to their oil to clean up dirty diesel rings, I've also poured ATF into the cylinders through the injector hole and left it for a few weeks, as well as ATF in my fuel.

 

[98G]

Do you get any light colored smoke for the first 30-60 seconds at cold start?
Or just the normal quick 2 second puff of black at start up while the governor adjusts itself?
If it smokes a little light gray/blue for 30-60 seconds, that's another indication of stuck rings = lowered compression.
You can also put a small piece of paper over the oil fill cap opening while running. A normal engine will tend to pull the paper against the opening while stuck rings will blow it away from the opening.
I know a couple guys who swear by Hot Shots stiction eliminator added to their oil to clean up dirty diesel rings, I've also poured ATF into the cylinders through the injector hole and left it for a few weeks, as well as ATF in my fuel.

My experience has been that 802s tend to have positive crankcase pressure even without stuck rings.

 

[DieselAddict]

Broken rings and stuck rings can have similar symptoms for a while. Long term broken rings will do a lot more damage.

I'd recommend pulling injectors and doing a borescope inspection. See if you have any vertical scarring on the cylinder walls that would point to a broken ring.

Edit:
If you have no scaring then play around and see if you can get them loosened up. Worse case you pull the pistons and fix the problem.

 

[Digger556]

Do you get any light colored smoke for the first 30-60 seconds at cold start?
Or just the normal quick 2 second puff of black at start up while the governor adjusts itself?
If it smokes a little light gray/blue for 30-60 seconds, that's another indication of stuck rings = lowered compression.
You can also put a small piece of paper over the oil fill cap opening while running. A normal engine will tend to pull the paper against the opening while stuck rings will blow it away from the opening.
I know a couple guys who swear by Hot Shots stiction eliminator added to their oil to clean up dirty diesel rings, I've also poured ATF into the cylinders through the injector hole and left it for a few weeks, as well as ATF in my fuel.

Ray,

It's light grey for ~3 minutes on startup or after additional load is added until the engine gets hotter. When I say additional load, my typical MO is to start the unit, let it warm up unloaded for 5 minutes or until coolant hits 120°F, then I add ~50% load (3kW) until the coolant is at operating temp (195°F), then I step up to 5kW for an hour.

Even at operating temp, jumping from 3kW to 4kW results in light grey for ~3 min. At 5kW it lightly smokes all the time. My good units do this too, Im at 5280 ft ASL, so we have less air up here

This one also has noticable pressure from the crankcase compared to my other 802a's.

I'm thinking its probably stuck rings and the next easy action would be pouring ATF into the cylinders.

 

[Ray70]

Interesting, never really thought much about differences in performance based on altitude, but makes sense.
If you go the AFT route, just be aware that the center of the piston is a big giant dish, so you need to add enough ATF to fill and overflow the dish in order for it to get into the rings.
If things don't work out with the ATF, pulling the pistons out is really not that big of a job, it's actually pretty easy.

 

[Guyfang]

Keep in mind, that after waiting how ever long you are going to wait, after pouring ATF, (or anything else for that matter) into the jugs, that you need to cover the injector holes with a rag, and turn the set over a little bit. Because there will be some fluid left in the jug. The rags will keep your ceiling clean.

 

[Digger556]

You guys are awesome as usual!

I'll pull the injectors and scope the bore to start, but probably will end up using ATF. How long do you typically let it set? This unit is a backup, so being down for a while is not a problem.

 

[Digger556]

Interesting, never really thought much about differences in performance based on altitude, but makes sense.

For N/A engines, you reduce power output by 3% for every 1000 ft of elevation. The LPW2 (DN2M) fixed speed version at 1800 rpm is rated for 12.5 HP cont / 13.7 HP int (fuel stop power) per ISO 3046

Based on calculations using BSFC, fuel consumption, known HP and electric load, I estimated the conversion from shaft power to electric output to be 76% for an 802a at 100% load.

So a 6.25 kW load at 1.0pf would require ~11.0 HP. The 802a is rated at full output to 4000 ft. At 4000 ft, max engine output would be exactly 11 HP. After that, the 802a is derated 3.5% per 1000ft and rightfully so. At my altitude, the engine can only make 10.5 HP, so max cont output would only be 6 kW @1.0pf. The manual says 5.97 kW @1.0 pf, so pretty close.

A unit at sea level would only be at 84% of max engine load at 6kW, but I would be at 100% with the same load. So I get a little more smoke.

 

[2Pbfeet]

For N/A engines, you reduce power output by 3% for every 1000 ft of elevation. The LPW2 (DN2M) fixed speed version at 1800 rpm is rated for 12.5 HP cont / 13.7 HP int (fuel stop power) per ISO 3046

Based on calculations using BSFC, fuel consumption, known HP and electric load, I estimated the conversion from shaft power to electric output to be 76% for an 802a at 100% load.

So a 6.25 kW load at 1.0pf would require ~11.0 HP. The 802a is rated at full output to 4000 ft. At 4000 ft, max engine output would be exactly 11 HP. After that, the 802a is derated 3.5% per 1000ft and rightfully so. At my altitude, the engine can only make 10.5 HP, so max cont output would only be 6 kW @1.0pf. The manual says 5.97 kW @1.0 pf, so pretty close.

A unit at sea level would only be at 84% of max engine load at 6kW, but I would be at 100% with the same load. So I get a little more smoke.

Do you know that for your Lister DN2M engine specifically? There should be a data plate on the enclosure.
The data plates that I have seen for other DN2Ms were not yet in derate at 4,000' and 95F, and only to 4.3kW at 8,000'@95F. So, a guesstimate derate would be closer to 4.7kW. (6% @ 6,000' and 95F).

Regardless, +1 on ATF in the cylinders for a while, and yes, do as @Guyfang recommends before starting. After that, I would treat this as an engine that needs to be broken in and I would run the unit fully loaded to seat the rings. If you have renewable diesel (not biodiesel) available locally, it combusts better than standard diesel, and will have less of an altitude derate. Plus, it should smoke less.

All the best,

2Pbfeet

 

[Digger556]

Do you know that for your Lister DN2M engine specifically? There should be a data plate on the enclosure.
The data plates that I have seen for other DN2Ms were not yet in derate at 4,000' and 95F, and only to 4.3kW at 8,000'@95F. So, a guesstimate derate would be closer to 4.7kW. (6% @ 6,000' and 95F).

Regardless, +1 on ATF in the cylinders for a while, and yes, do as @Guyfang recommends before starting. After that, I would treat this as an engine that needs to be broken in and I would run the unit fully loaded to seat the rings. If you have renewable diesel (not biodiesel) available locally, it combusts better than standard diesel, and will have less of an altitude derate. Plus, it should smoke less.

All the best,

2Pbfeet

The 3%/1000 ft derate is universal for normally aspirated engines, ignoring engines with tuned intake runners which this engine definitely doesn't have. I didn't make it super clear, but I was comparing this universal way of altitude derating an engine to the official way the 802a is derated on the name plate:


The 802a isn't derated at all until 4000 ft, but this is a result of the engine having some power in reserve at sea level. When showing the official derating above 4000 ft, I did the math and found it to be 3.5%/1000ft from 4000-8000ft. The results closely mirror the universal way of calculating derate, but the universal way is more accurate if you understand what HP the engine is actually working with at sea level. I pulled that data from Lister's website.

Good to know on the renewable diesel. I will check around town. Do you know how it compares to conventional diesel for long term storage?

 

[2Pbfeet]

The 3%/1000 ft derate is universal for normally aspirated engines, ignoring engines with tuned intake runners which this engine definitely doesn't have. I didn't make it super clear, but I was comparing this universal way of altitude derating an engine to the official way the 802a is derated on the name plate:
View attachment 933128

The 802a isn't derated at all until 4000 ft, but this is a result of the engine having some power in reserve at sea level. When showing the official derating above 4000 ft, I did the math and found it to be 3.5%/1000ft from 4000-8000ft. The results closely mirror the universal way of calculating derate, but the universal way is more accurate if you understand what HP the engine is actually working with at sea level. I pulled that data from Lister's website.

Good to know on the renewable diesel. I will check around town. Do you know how it compares to conventional diesel for long term storage?

I agree with you on the derate; I have had other engines that weren't tuned and didn't derate until over 10,000', which I think had to do with the ability of those engines to ignite well in lean atmospheric conditions at sea level. I tend to be on the trust, but verify page...

Renewable diesel is a fuel made by fully hydrogenating vegetable oil, so it doesn't oxidize. (In the US it is only made by Neste at the moment, AFAIK.) It is still somewhat hygroscopic, but less so than Dino diesel or biodiesel. Because it has no aromatics, and is fully hydrogenated, as far as I can tell from the chemical analysis, it should be better than regular diesel for longer term storage. However, I would still keep it in sealed tanks, if possible. (I use NATO Jerry cans, though I'm considering a Type S FuelCube, which it is pricey, but secondary containment and legal transport is worth a lot to me.)

All the best,

2PbFeet

 

[Ray70]

How long do you typically let it set? This unit is a backup, so being down for a while is not a problem.
[/QUOTE]
I'd let it sit a week minimum, the more the better.
Not sure of your machine's overall condition but being a 94' you should consider replacing the 3.5mm fuel return lines while you have the top cover off, since you will be right there with the injectors already disconnected.
Cheap insurance against the inevitable future fuel line leak!

 

[2Pbfeet]

I'd let it sit a week minimum, the more the better.
Not sure of your machine's overall condition but being a 94' you should consider replacing the 3.5mm fuel return lines while you have the top cover off, since you will be right there with the injectors already disconnected.
Cheap insurance against the inevitable future fuel line leak!

Noted thank you!

The machine is in really good shape for its age. Ignoring the faded control panel and slightly weathered paint, it looks as good as my late-model units. I'm not sure why the rings are stuck, but the engine shows all signs of being healthy. Oil pressure is 60 psi cold/50 psi hot, it fires up easy, crankcase is clean, etc.

I replaced the 3.5mm lines, but of all my units, this one had the least issues with fuel lines. My newest one, a 2011, had the most rotted lines. Sorta ironic.
[/QUOTE]
Long periods of non-usage and/or cold use could easily do it, especially if that was preceded by low load usage.

JP-8 is quite hard on rubber, so it would not take much JP-8 exposure to do a number on the fuel lines.

All the best,

2Pbfeet