Hoping to find an old cummins guy. seems like they are getting few and far between. Have an 89 freightliner with a Big cam Cummins NT855. It started knocking the other day. I listened for a minute and determined that it was in the front of the engine. Pulled cover and Jake body on Cylinder 1/2 and the #1 injector push rod was knocking with a pretty good space between it and the rocker. with the engine running, I can touch the rocker and I mean almost no pressure and it quits. I pulled the push rod and it was bent. replaced it with another and it still has a pretty good bit of slop even with adjusting screw bottomed out. My question is should I automatically assume the cam is "lobed?" or should I look elsewhere first. Apears to have top stop injectors. I am unfamilliar with these injectors and engine and am curious if this can happen if the injector spring is bad? any help would be great.
Well If the adjuster is sunk into the rocker with a straight pushrod the cam is rounded. You can pull the oil pan and visually see to confirm. Do you have a ESN# Is the fuel pressure turned up? More than likely.. Everybody thinks cummins had "soft cams" The problem is if you increase rail pressure you must reflow your injectors otherwise pushrods bend and cams round.
I do. ESN is:10658811 I am going to have to pull the pan I think. We have had the truck for 8 years or so, and never had a problem. We have never turned up fuel pressure. I am leaning really heavy towards rounded cam, but was hoping for something easier. With these injectors, I am currious, is there a return spring? Just wondering if it is even a possability that the injector is not all the way up? just wishful thinking? Thanks for your response. I am going to keep checking and will post here if I find anything else.
I've heard and loose adjustment on the Jake brake will do that also.
The Cam followers can wear out also and the shaft the follower runs on.
If you have a dial indicator. Set up the jig on the bad hole and a good hole. Measure the travel of the rocker on the injector side. You should have .224 travel unless its a BC4 that has .266 Yes the injectors have springs in them. I ran the ESN and this is what came up...??? Marketing Model Name Service Model Name EPA Model Name NTC290BC NH/NT 855 Not Available Shop Order Build Plant Build Date SO18696 CEP - Columbus Engine Plant 20 Jun 1977 Warranty Start Date ECM Code Fuel Pump Part # Not Available Not Available 3004188 Fuel Pump Calibration Marketing Engine Configuration # Technical Engine Configuration # 3114 Not Available D092244BX02 CPL # Customer Number Customer Name CPL233 Not Available 01401
Set up the dial indicator and check travel. Check your oil and see if it is over full, possibly a stuck injector. When you bar the engine over, check and see if the injector comes up about the same as #2.
Set up the dial indicator and check travel. Check your oil and see if it is over full, possibly a stuck injector. When you bar the engine over, check and see if the injector comes up about the same as #2.
I talked to my boss. I guess he put that engine in about 10 years ago, before I got here when the original crapped.
I am going to measure the rise in the injectors right now. Thank you for all of the Resopnses. I will update when or if I find the problem.
Update: Problem Solved. Pulled injector, Plunger was broken and injector jammed. link was damaged and rounded. Had to wait over a week for a replacement (Thus the reason it took so long to update this) when the new one got here I measured the max upward travel. broken injector was at .434, new one was .332 that is about the gap I had to begin with. replaced the injector and ran the overhead again. So far it is working like a champ. Thanks for all of the help!