24v 5.9 Cummins - Winter Project

[Sask466]

Cylinder #1 is the the worst.  The rest look heavily glazed and very little scoring.  Some light scoring on 1 (looks worse in pic) and it has some ring ridge.  
 

Pistons are next, maybe later this week. 

[Sask466]

Also, observations of a IH DT guy:

It’s amazing how much power these modern (20+yrs old now) 24v 5.9’s can make, when you compare them to the construction of a 466.

For example, the intake port design must be terrible for flow, if you ask me.  The way the air has to bend around that intake plenum seem odd to me.  

 

[Gearclash]

Now you know why, at some point in the pursuit for greater horsepower out of a B series Cummins, the intake plenum is cut off and replaced with a bolt on fabrication with much better flow. 

[Sask466]

4 hours ago, Gearclash said:

Now you know why, at some point in the pursuit for greater horsepower out of a B series Cummins, the intake plenum is cut off and replaced with a bolt on fabrication with much better flow. 

Really?  I did not know that!  Otherwise it seems like an easy enough/straightforward motor.  It’s sure nice and compact compared to other ag/indutrial diesels in the 6 to 8L range.

[Sask466]

#1 is below.  #6 ring is in many pieces as well. 

 

The rest of the cylinders top ring is in 2 pieces:

 

[dale560]

4 minutes ago, Sask466 said:

#1 is below.  #6 ring is in many pieces as well. 

 

The rest of the cylinders top ring is in 2 pieces:

 

 An you post pictures of the rings. Did they break coming out or were they broken in engine? That is more common than you think. Also is pickup got a tuner. That one piston looked to have a star in piston top. That is definitely warranty void in other models.

[Sask466]

Those rings were broken in the pistons - they came out in pieces as we pushed them out.  

This truck has never had a tuner as far as we know - original owners.  The injectors are likely dirty if that affects pattern not sure - it hadn’t run for a few years very much.  

The star pattern you refer to, I dont totally follow - I will post more pics of pistons in a bit.  

[dale560]

56 minutes ago, Sask466 said:

Those rings were broken in the pistons - they came out in pieces as we pushed them out.  

This truck has never had a tuner as far as we know - original owners.  The injectors are likely dirty if that affects pattern not sure - it hadn’t run for a few years very much.  

The star pattern you refer to, I dont totally follow - I will post more pics of pistons in a bit.  

They will break as they hit the ridge on top. I think I can see the soot buildup in the ring groove on one piston. You really have to look at the rings. If they were broke and ran or broke on the way out.

the star pattern is faintly visible on top of one piston. It comes from fuel spray out of nozzles. On hopped up engines it will burn a nice pattern. Most mfgs have a guideline to deny warranty on any engines displaying that pattern. Google tulip or star pattern. The 6.0 land 6.4 power stroke had those issues always when chipped

[Sask466]

Regarding the rings item - I looked at the ends - they are shiny and smooth, so they look to have broke some time ago to me.  We were also pretty gentle with removal - I scraped all the carbon off with a razor prior making removal low-violence. 

I will do more digging on the spray patterns.  Not an area I am well versed in.

Thanks for the input!
 

[dale560]

8 hours ago, Sask466 said:

Regarding the rings item - I looked at the ends - they are shiny and smooth, so they look to have broke some time ago to me.  We were also pretty gentle with removal - I scraped all the carbon off with a razor prior making removal low-violence. 

I will do more digging on the spray patterns.  Not an area I am well versed in.

Thanks for the input!
 

The spray pattern on yours isn’t a big deal. Barely visible but just enough is why I asked if it wa chipped. About 10 years ago in the trade magazines they would have pictures of chipped power stroke pistons in for warranty. They would have a blue to purple tulip in them. Can’t find a picture though.

[Finney]

i have owned 3 24 valve trucks and still own 2. The 2,000 is my welding truck with 358,000 miles on it. I bought it on Ardmore OK with 2,000 miles on it in 01. It is stock with marine injectors.

The 2001 used to be a welding truck but is now a toy with twins and P pump. We melted the piston tops after turning the screw out a tad too much.

The 2nd 2001 was replaced with a Duro-Junk and still got it. (bad move). The Duro rides and drives better but costs a lot more yearly in operating and maintaining.

After figuring out the VE pump didn't like the low sulfur fuel and adding 2 stroke oil all problems stopped. I like the VE pump. 

[dale560]

Been looking up probable causes of your broken rings. A lot of information out there on places. First it seems the 5.9 likes to break rings on 1 and 6 sometimes cyl 5 also. A good explanation of this was posted on another forum. The injectors or drivers in ecm fail. Leading to poor fuel injection this causes some issues with cylinder running drier as some of the preburn fuel and after injection cycle fuel is needed to lube top rings. The oil control package is pretty good to control emissions so oil doesn’t get to top rings as older engines. The rings then break from ignition residue and other processes. Cummins had a ring material redesign in 2005 to help with this but is not mentioned in many places. 
So the consensus is on the 100,000 mile engines with ring failure it was either tuning chip or failing injector that caused the problems.

[Sask466]

Thanks for this info - we plan to send injectors with fairly reputable place on the west coast - test and either rebuild/replace.  The drivers in the ecm going bad is something I hadn’t stumbled across yet, I will look into that more.  Maybe it can be tested?

#1 and #6 rings were the ones in pieces - the rest of the cylinders were “only” broke in half.  My gut feeling is #1 and #6 may have already been broke for reasons you mention, pre-overheating. The rest may have broke as a result of heating.  

This truck is manual, and she used to pull a big horse trailer all over the place (California/Florida from the prairies) .  I wonder if it had been lugged a fair bit. I bet it may have been.  Nobody would have told her not to I’m sure, and these motors don’t have an EGT gauge.

I have also read some folks go to a marine piston, as they may have a more robust ring and ring land design - these truck 5.9’s were a compromise in piston design for emissions reasons possibly I gather. 

I find it’s hard to research this stuff now - Google pushes AI answers and seems to hide actual information.  

We have some good rigid hones we have been using, as well as a bore gauge.  They bores are cleaning up to a point they will be okay I think.

[Sask466]

Getting better:

[Gearclash]

Lugging a 5.9 in a pickup is not a good idea.  I have a pyro on my 1999 5.9.  I can run the engine as hard as I want and have a very comfortable EGT -- provided the engine speed is kept up.  Really need to be at or above 2000 RPM for safe maximum power.  This is a manual and if I kick it up to 5th gear at 900 RPM and put the narrow pedal to the floor on a wet gravel road up hill the EGT will be in the red shortly.  Pulling a loaded trailer at 60 MPH, going from 4th to 5th means the EGT will go up about 150-200*F.

To the OP, I would be suspicious of injector problems on the more damaged cylinders.  Common rail fuel systems are unforgiving of bad injectors.  Seems to me also that the early Cummins common rail systems did not have a tight enough fuel filter.

Also read this tidbit about the common rail 5.9 -- don't rush engine warmup.  Apparently if warmup is too rapid, cylinder #6 can be too hot before the thermostat opens enough. 

[dale560]

2 hours ago, Sask466 said:

Thanks for this info - we plan to send injectors with fairly reputable place on the west coast - test and either rebuild/replace.  The drivers in the ecm going bad is something I hadn’t stumbled across yet, I will look into that more.  Maybe it can be tested?

#1 and #6 rings were the ones in pieces - the rest of the cylinders were “only” broke in half.  My gut feeling is #1 and #6 may have already been broke for reasons you mention, pre-overheating. The rest may have broke as a result of heating.  

This truck is manual, and she used to pull a big horse trailer all over the place (California/Florida from the prairies) .  I wonder if it had been lugged a fair bit. I bet it may have been.  Nobody would have told her not to I’m sure, and these motors don’t have an EGT gauge.

I have also read some folks go to a marine piston, as they may have a more robust ring and ring land design - these truck 5.9’s were a compromise in piston design for emissions reasons possibly I gather. 

I find it’s hard to research this stuff now - Google pushes AI answers and seems to hide actual information.  

We have some good rigid hones we have been using, as well as a bore gauge.  They bores are cleaning up to a point they will be okay I think.

Just for a tip. I follow some of the Dave’s auto center stuff. He always talks about the 5.9 and 6.7 they give it 2 thousands extra clearance on 5 and 6 because of cooling system issues.

[Sask466]

Awesome stuff - thanks to all (and specifically Gearclash and Dale) for all the help.

Merry Christmas All!!!!

[Diesel Doctor]

On 12/16/2025 at 8:23 AM, Gearclash said:

Keep us posted.  I have the CDC version of the 5.9 in a CIH tractor that I may have to pull apart this winter.  It has a massive amount of blowby, such that it will blow its engine oil out at the rate of a gallon an hour.  Adding a second blowby vent has stopped most of the oil loss but the underlying problem still exists. 

5.9s don't take kindly to being overheated severely while under load.  My brother had a 5.9 in a tractor take out a couple cylinders because the cooling system was underfilled due to an air pocket after radiator work.  Tractor was on a mixer wagon so there was no one watching the temp gauge when it was first loaded up. 

I have heard marine pistons may be tougher so what about the Ag pistons?

Is there a better mouse trap out there that can make a more bullet proof engine?

Breaking rings would have me looking hard at the injectors.

[Gearclash]

1 hour ago, Diesel Doctor said:

I have heard marine pistons may be tougher so what about the Ag pistons?

Is there a better mouse trap out there that can make a more bullet proof engine?

Breaking rings would have me looking hard at the injectors.

The Ag versions of the 5.9 were generally the lowest rated HP.  The highest I know of was 180 or a little better in the JCB tractors, all the way down to about 85 HP in a CIH 5130.  In the second gen Dodges, that same engine was running from 215 in front of the 47RE automatic up to 245 in front of the NV5600 6 speed.  Then there was a significant bump again after 2002 when the common rail engine was introduced.  I think the last iteration of the 5.9 in a pickup was running 325 HP.  Even in a medium duty truck those engines were set at 220 HP.  

Best information I can find on the net suggests Cummins set the marine versions of the 5.9 up to 480 HP.

Just for fun.  The general public issue Detroit Diesel 6-71 was set for 238 HP in later non turbo versions.  In marine trim, the 6-71 was taken up to an eye watering 485 HP . . . and I have seen a video of a freshly rebuilt marine 6-71 pulling 515 on the dyno.  The TBO at that HP level is pretty short . . . 

[jass1660]

Marine applications are always the highest horsepower as they have unlimited cooling due to being in boats.

[Sask466]

There is a ton of info on these engines out there, almost as much conflicting info, and a ton of bad info.  I did find a fellow that runs a machine shop on YouTube that seems quite knowledgeable. 

There was also a 305hp version of the 5.9 at the same time there was a 325hp version.  The 305 hp version had a much smaller bowl and seems like a tougher/thicker piston top?  305hp is on the right.

 Also the 305hp injectors were 8 hole with a different spray angle - the 325hp ones are 5 hole.  Swapping to the wrong injectors is another recipe for disaster. 

It’s sort of wild how prevalent this ring issue is, and how highly this engine is still regarded.  This is a $5k to $10k failure that seems to happen quite often.  

*edit - this engine also doesn’t have a pryrometer!  Not even a sender that goes back to the ecm.  So if there is a temperature issue there isn’t anything the driver or computer can do about it.  

[dale560]

25 minutes ago, Sask466 said:

There is a ton of info on these engines out there, almost as much conflicting info, and a ton of bad info.  I did find a fellow that runs a machine shop on YouTube that seems quite knowledgeable. 

There was also a 305hp version of the 5.9 at the same time there was a 325hp version.  The 305 hp version had a much smaller bowl and seems like a tougher/thicker piston top?  305hp is on the right.

 Also the 305hp injectors were 8 hole with a different spray angle - the 325hp ones are 5 hole.  Swapping to the wrong injectors is another recipe for disaster. 

It’s sort of wild how prevalent this ring issue is, and how highly this engine is still regarded.  This is a $5k to $10k failure that seems to happen quite often.  

 

I think the ring issue is common to how that pickup was run. Long trips on interstate , keeping up with traffic so they tend to get high egt temps and they don’t realize it. They tend to run forever with the short trip older slow driver.

[CIHTECH]

1 hour ago, Gearclash said:

The Ag versions of the 5.9 were generally the lowest rated HP.  The highest I know of was 180 or a little better in the JCB tractors, all the way down to about 85 HP in a CIH 5130

Years ago a couple customer manure haulers ran JCB's. We had them tweaked pretty strong, had to play with timing to keep EGT's in spec. 

We've seen a lot of failures of the piston rings as well, most times on #6 cylinder. Fixed bore hone in-frame until they "clear out" then measure, if they are still under MAX bore size we build them back and send em out the door. 

All in all it's still at the top of my list for the "best little engine that could" 

 

[Shell1066]

Wish Ford would have factory installed that engine in their 90 model trucks. While the 7.3 is good , they would have had a very sought after truck now. Fil has a 97 3500 that has over 300000 on the motor from steady hauling cattle and flat bed. It's turned up and has never been rebuilt. Trans has lost 5th half dozen times but that motor keeps ticking. 

[Sask466]

22 hours ago, CIHTECH said:

 Fixed bore hone in-frame until they "clear out" then measure, if they are still under MAX bore size we build them back and send em out the door. 

 

Did your shop have a number on what max piston to wall clearance is?  I can’t find a Cummins spec.