Replacing a NHC 250 with new drop in engine

[jaws4518]

So, I ignored a high oil pressure reading for 6 months because I thought I had a faulty gauge. There was a period of time were the gauge was not reading then it came back to life many running hours later. This whole scenario started a year before I lost my engine back in October 2025. I'm going to say two years ago I started hearing this pinging sound during a hot engine idle. It pinging sound got a little worse over time. I concluded with others that it was the dampener failing. I got a new dampener to replace old one with last summer. Somewhere last summer I started having high oil pressure reading but the engine was running fine. The day I realized something had happened there was a shutter going down the Hwy, not much more than that. When I got to my destination about 10 minutes later there was a horrible knocking at idle. At a higher rpm you can't hear it. When I got back to the yard, I checked the oil. It was Milky. Got radiator fluid in my oil that I just changed. A gallon of Lucas to boot. I just spent $250 on oil change and I have blown engine. Thankfully it is not seized otherwise it will be very difficult to pull.
So, I have a new replacement in the container. It will need hand turning and some maintenance to get it ready. I have some retired military mechanic support who worked on 800/900 series trucks, but they are so busy. I have the equipment and facilities to pull and replace but I would appreciate any advice or experience that a someone has to offer. The brand new engine has been sitting in the container for 15 years.

The old engine has only 540 hours. It had only 17 hours on it when I acquired the M929-A1 dump. I took it from a break-in to its demise. It has been strong engine all the way... Very sad! It's not just a blown head gasket, it sounds like a rod bearing...? Who knows? Maybe this has something to do with the pinging sound that started 2 years ago? Cavitation? Hole in the block or sleeve? I have had no sign of radiator fluid in the oil up to the engine failure. The engine will start, but it sounds like it wants to through a rod.

 

[jaws4518]

I hope some member out there has experience with a drop-in? It would be nice to hear someone's success or failure comments. I will be searching the forum for engine replacement threads. Will be looking at the TMs too.

 

[WillWagner]

Where did the "new" engine come from? A spun bearing will not usually cause coolant in the oil unless the rod contacted the liner and it broke, if that happened, usually a ventilated block happens.

Most likely happened the other war round, coolant in the oil, loss of lubrication, then spun brg.

BUT the knock you hear COULD be a scored piston which will give you a knock and put coolant in the oil. The "ping" you heard could have been a failed injector, but that is usually accompanied by white, black, heavy grey smoke. PT injectors can blow the tip off of split the cup.

Have you jacked with fuel delivery?

Cut the oil filter open and see what type of metal is in it, that will point you in the right direction for repair. Easier to repair in chassis, if a bearing isn't out of it, than swing an engine, especially an engine that has been sitting and you don't know its history.

 

[Superthermal]

I have a good engine in my rig that might be a good trade for someone down the road, that is other than it seems wimpy/gutless for the M813 of mine that it is in LOL.
I have hoped to do a big cam swap for mine... just dreaming here.
Best wishes on what you do for the fix or swap. I know a guy from California with an 8 series dump that did an in-frame with some upgraded pistons and such, basically making a big cam out of his rig. No oilers though for the pistons... He tossed in a turbo and some injector upgrades and it is flying!

 

[jaws4518]

Where did the "new" engine come from? A spun bearing will not usually cause coolant in the oil unless the rod contacted the liner and it broke, if that happened, usually a ventilated block happens.

Most likely happened the other war round, coolant in the oil, loss of lubrication, then spun brg.

BUT the knock you hear COULD be a scored piston which will give you a knock and put coolant in the oil. The "ping" you heard could have been a failed injector, but that is usually accompanied by white, black, heavy grey smoke. PT injectors can blow the tip off of split the cup.

Have you jacked with fuel delivery?

Cut the oil filter open and see what type of metal is in it, that will point you in the right direction for repair. Easier to repair in chassis, if a bearing isn't out of it, than swing an engine, especially an engine that has been sitting and you don't know its history.

I haven't even tried to diagnose yet. I really don't know much as of now. I believe there is coolant in oil but I will verify again and report back. Have "not" jacked with the fuel delivery. I will follow your advice and start with the oil filter. After that we pull the pan and the head, or heads?

The engine in the can came from the depot in El Paso 2010. Got all the paper work on it. Last resort I guess.

 

[WillWagner]

Cut the filter open so you can see what type of material is in it. Then drop the pan and look up her skirt. If it spun a brg, no need to waste time yanking heads.

 

[jaws4518]

I haven't even tried to diagnose yet. I really don't know much as of now. I believe there is coolant in oil but I will verify again and report back. Have "not" jacked with the fuel delivery. I will follow your advice and start with the oil filter. After that we pull the pan and the head, or heads?

The engine in the can came from the depot in El Paso 2010. Got all the paper work on it. Last resort I guess.

Maybe it won't be as bad as it sounds. From they way it sounds it is the 2nd or 3rd cylinder. I think the pinging sound that started in 2023 has something to do with this. Yes, major blow-by I guess? That sleeve might have a hole or crack in it? I think the erratic oil pressure reading started around the same time. Everything that I remember seems to be coming together. My oil pressure gauge quit working then month or so later it woke up and was reading normal 40 running and 60+ at startup. Maybe 90 until warm? Like I mentioned, the high oil pressure reading started at the beginning of 2025. It started creeping up to 90 and 100. That went on for several months with limited use. The day it was pegging 120+ gauge was when I felt something and noticed the loud knocking sound at an idle. It has been parked ever since. That would be nice if it is just a

Cut the filter open so you can see what type of material is in it. Then drop the pan and look up her skirt. If it spun a brg, no need to waste time yanking heads.

10/4! I will do that and follow up with this post. Not sure when I will put in the shop over the well, but I can certainly pull the filter canister to see what is there. I hope the damage is minimal but I a prepared for the worst. It will start and run, but there is no need to start again until I know more. I will hook up the tow bar and pull it into the shop.

 

[WillWagner]

High OP will not cause issues. If the engine still runs, damage is done, pull the lids and use a 3/4 socket on an extension on the injector adjusting jamb nut and push the lever down, push the ext. toward the exhaust side, while it is running. The knock should go away when the injector is shorted. That will be your problem cylinder.

Another way to tell where the issue is is to look where the most vapor is coming from, it migrates up the push tube cavity where the failed cylinder is.

 

[jaws4518]

High OP will not cause issues. If the engine still runs, damage is done, pull the lids and use a 3/4 socket on an extension on the injector adjusting jamb nut and push the lever down, push the ext. toward the exhaust side, while it is running. The knock should go away when the injector is shorted. That will be your problem cylinder.

Another way to tell where the issue is is to look where the most vapor is coming from, it migrates up the push tube cavity where the failed cylinder is.

Very good! I will follow this procedure when we pull it into my new shop. I haven't even used it yet. Need to set it up. I built it for MV restorations and equipment maintenance. I will report back with the results.

 

[Mullaney]

Very good! I will follow this procedure when we pull it into my new shop. I haven't even used it yet. Need to set it up. I built it for MV restorations and equipment maintenance. I will report back with the results.

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Nice... Really Nice building!
AND you even have a Pit!!

I started the permitting process here in the great state of Mecklenburg a little over a year ago. Still waiting on permits. Their latest round of hassling me is an 8 foot sidewalk with an 8 foot planting strip with city approved trees in there. Just trying to build a simple 50x100 foot building behind our already existing structure. FUN and Excitement LOOMS ahead...

 

[jaws4518]

.
Nice... Really Nice building!
AND you even have a Pit!!

I started the permitting process here in the great state of Mecklenburg a little over a year ago. Still waiting on permits. Their latest round of hassling me is an 8 foot sidewalk with an 8 foot planting strip with city approved trees in there. Just trying to build a simple 50x100 foot building behind our already existing structure. FUN and Excitement LOOMS ahead...

Thanks! This is out in the country so I only have to get county approval on a septic system. I decided to go without utility infrastructure because I have MEP-003A generator. The pad is on the backside of the building with is facing North. I will install a NEMA gutter box back there. The pad is big enough for 2 generators. It's nice having that harbor freight 13KW generator as a mobile backup. I can move that gen set around if I need too.

Here is the bottom of the mechanic's well. Grate goes over the drain. I can spray wash underneath. See, I haven't even cleaned the well out yet. Got two mummified kittens down there. The concrete dried them out quickly.

Anyway, I will get the M929_A1 in there next month. I will open up the oil filter canister this weekend sometime.