Cummins 250 Fuel Injectors

[fuzzytoaster]

I've got a M923 fresh from overhaul that is missing on 2 cylinders, confirmed with a temp gun. I thought I got lucky when I got a box of fuel injectors for a good price through GL but it appears I've hit a snag. NT855 vs NTC855. The heads of the injectors are different though everything else fits perfect. The info on the new injectors shows it's for the M939 series truck and it indeed fits perfect except it's 1/2" taller and doesn't fit with the holding bracket (to wide). Has anyone else had this issue? Solutions? New holder source? Anyone got the correct injectors?

Also any tips on getting the #6 rear injector under the cab/firewall?

 

[wrenchturner6238]

The one you call as new is a top stop injector and your old one is a type D injector and if that is what it has in the engine that is what you should replace it with. As far as I know you can't use 1 in place of another.

 

[machinist75]

I had to replace the #5 liner on mine and I can tell you getting that rocker box of is a pita. If I remember right I removed it to the drivers side, couldn't get it off the passengers side. Putting it back on is a pain in the butt also, getting all the rockers back where they need to go. I didn't seat one of the rockers right and bent one of the push tubes, easy enough to replace but a pain no less. I would do a complete a top set adjustment of all the rockers and injectors, it's not that difficult once you get your brain wrapped around it.

 

[wrenchturner6238]

Just a question. I have only ran the overhead on mine so far and when I jacked up the cab with the jack bolts it seemed to help. Are you taking the cab mounts loose and jacking up the cab as high as you can? It may be better if you would take the center rocker box off as well.

 

[gimpyrobb]

Just a question. I have only ran the overhead on mine so far and when I jacked up the cab with the jack bolts it seemed to help. Are you taking the cab mounts loose and jacking up the cab as high as you can? It may be better if you would take the center rocker box off as well.

This.

 

[56GELOCO]

I know this is an older post, but I'm in the same boat as fuzzytoaster was with the different injectors. No one ever said if the newer ones were useable.

 

[fuzzytoaster]

The injectors could be used in a pinch but mixing the two types would be bad as they actually inject a slightly different amount of fuel into the cylinder and a different "pop off" psi. Replacing the entire set of them shouldn't be a problem as I've pulled both types from the 855 blocks on the 939 series trucks but finding the correct corresponding injector hold downs is another story. If its got one type just replace it it that type - KISS method. Did the truck run with mixed style injectors in? Yes. Any smoke etc? No. I did feel the engine didn't idle as smooth as some of the others and replaced them with a refurbished part for $50 w/o core charge. Again KISS. Hope this helps.

 

[56GELOCO]

Thanks for the fast reply. Long story short, The company I work for has an old 56 model GE locomotive that we use to move rail cars around in the plant and one of the NHC250 engines ate the crank up. We had a 95 model propane generator with 75 hours on it so they had me to tear it down and to convert it to diesel to get the Locomotive back up and running. Everything is new and ordered from Cummins but these were the injectors they sent. Wasn't sure if I just needed the hold downs for them or to send them back.

 

[WillWagner]

Top stop and non top stop can be used together. No "pop off" pressures in them, that is generated by cam lift. You just need to use the outer base circle method to adjust them.

post the p/n on the one on the right and I can tell if they are NHC injectors. Remember, there were big cams in use so the top stop injs you have could be for a 400 BC


3054071 is for ntc400 bcII

 

[56GELOCO]

The injectors I received from Cummins are like the ones on the left, part #3046281PX. The injectors on the right are like the originals. The only number I can find on them are 185138 and 185139, which I can only match up to the injector body.

 

[simp5782]

Use non top stops 3054250 (PX) Prior to serial # 11246663

Use top stops 3046281 for units after serial 11246663