Cummins 250 injector plungers can go where they don't belong

[70deuce]

While pulling the 2 rear injectors to swap with the 2 front injectors to trace "cold cylinders" (the 2 rear are running way cooler than the other 4 as measured with an IR thermometer), the number 2 injector plunger decided to fall out on me and drop through the rocker box, pinball around down by the cam and drop into the oil pan. Hate when that happens!!. You get to practice changing the oil AND removing and replacing the oil pan. The little bugger landed in the large flat tray forward of the sump section of the pan so there was no chance of fishing it out with any magic wand. Thankfully it went all the way through to the oil pan. Afeter the practice on the oil pan and some $$$$ for 24 quarts of oil I did isolate my cold cylinder problems to the injectors. 1 and 2 and now the cold cylinders so I will be pulling all 6 for rebuild. Oh yeh, you get to practice adjusting the valves and injetors when you need to swap or pull injectors. Just wanted to tell everyone to watch out on dropping anything through the rocker box. There are fairly large openings where all kinds of things can go to the wrong place. Photos included are the culprit plunger and the rocker box that sucked the thing in.

 

[WillWagner]

RE: Cummins 250 injector plungers can go where they don

That is the link, not the plunger. It is an ugly thing to lose one of them down the push tube cavity! If you ever work on an STC engine, gaurantee you'll do it again! The links are only an inch long.
BTW, it is normal for cyls 1 and 6 to be colder than 2 and 5. 3 and 4 will be the hottest.

 

[70deuce]

Will, 5 and 6 were running almost 100 degrees cooler and that has transfered to 1 and 2 with the injector swap. Those 2 injectors aren't doing their thing. I have always felt this motor wasn't performing as it should. Will get these 2 and eventually the rest checked. And I won't be dropping anything else in to that engine.

 

[supermechanic]

After all parts are checked and up to par, do yourself the biggest favor possible and set the injectors by the height method.
Torque setting will get you close, but to get the smoothest idle, and best power, I've always found setting with a dial indicator to be the best.
The TM for this engine has all the info needed to walk a first-timer through the procedure.
You won't be sorry for the extra time spent doing this.

 

[70deuce]

Supermech, that way of setting those injectors certainly must be a better way to set them than the torque method I'm sure. It has to improve consistency across the cylinders hence the smoother idle I take it. I have become well versed in the torgue method but and willl try the height way. I know this motor is down on power even at our 6000 feet altiitude south of Denver and it really shows pulling this trailer. Anything to get some more juice out of this motor is worth it. Thanks

 

[Gamagoat1]

According to TM9 2320-260-34-2 there are two types of injectors in the NH250 Cummins.
The Stop Top and the Non Stop Top.
The Non Stop Top is properly adjusted by the dial indicator method but the Stop Top is not. "Tighten adjusting screw (STOP TOP#3) 5-6 lb-in. (0.6-0.7 N•m)." is the only adjustment figure given for the stop top.(page 3-246) The plunger travel settings are set up on a special machine OFF the engine.
The Non Stop Top's plunger travel is set up on the engine, that's what's being accomplished with the dial indicator.

 

[WillWagner]

With the torque method, the injector is set on the outer base of the cam profile, in other words, when the injector plunger is at it's farthest point into the injector cup. When setting the injector using the dial ind. method, the injector is set with the cam on the inner base of the cam profile. Top stop injectors shouldn't be set using the D I method, let the top stop do it's job. non top stops can be set either way. The torque method bottoms the inj. plunger in the cup. If it has been running loose and the cup is carboned, it will force carbon into the holes in the cup and can cause smoke, rough running and low power. Setting them by the D I method is good, unless the cam lobe is failed..as in pieces parts flaking off of it. Then the injector won't bottom in the cup because it was set on the inner base circle. Both have pros and cons. I prefer the torque method. You get the same set on all cyls and the tune up tends to last a bit longer.

 

[Gamagoat1]

Thanks Will!!

 

[70deuce]

Got the two suspect injectors back and in the motor and what difference! The motor runs much smoother and pulls much better on hills. Set them by the torque metod for now at 60 inch pounds. The local Cummins experts suggest this setting for these motors. Now need to get the other 4 done because it was discovered by the diesel shop who did my work that both injectors I gave them had different and the incorrect tips. One had 6 spray holes and one had 7. 8 is the correct number that came up for my serial numbers on the pump and the engine. One was even pushing fuel out of the top. That one was my "dead" cylinder for sure as measured with the IR thermometer. The shop said I was lucky if I was running on 4.5 cylinders with the two injectors I gave them. At 6500' MSL that puts this motor way down on power. The temps measured on the exhaust manifold are all pretty close now except for one cylinder which is not one of the "new" injector cylinders but I can tell by the off idle response, the consistent smoke flow and the pulling power that all 6 are firing somewhat. The cool one is 50 degress cooler than the rest. I'm going to have the shop go through the 4 other injectors and the pump after the Veterans Day festivities. I will be pulling the 38 foot van trailer about 90 miles round trip this Saturday to the Colorado Springs Veterans Day parade. Will definitley test out the motor then. Pics are attached of the rehabbed injectors.