Exhaust temperature, bad injectors, and an old Cummins

Hi everyone, here's a question for you...

I have a small-bore, small-cam, non-turbo NHC 250 that ate a piston and cylinder due to a bad injector.

I replaced the liner and piston etc. and got rebuilt injectors for the two cylinders underneath that cylinder head.

The engine runs much better now But it still smokes a lot and kind of farts around until it is right up to 180 degrees water temp.

With an infrared thermometer, I measured the temperature of the exhaust manifold while the engine was warming up in front of each cylinder and found that the two cylinders with the new injectors were running about 20 degrees C cooler than the other four cylinders. That is, they were at 80 degrees C rather than 100.

To set the two injectors I replaced I just kind of guessed at the preload by comparing it to the other four injectors, so there is a chance that the new injectors aren't set properly.

However, it WAS a bad injector that overheated and melted the piston I replaced. And when I jazz the throttle with the hood open, all the rattling comes from the four cylinders with the old injectors whereas the two jugs with the new injectors are nice and quiet.

What do y'all think? Are my two new injectors adjusted poorly, causing poor combustion until the engine is hot? Or do I have four old, faulty injectors that are in the process of overheating and destroying the other four pistons?

I realize this is all conjecture, but I want to know what you have experienced. Thanks for your responses.

Cheers,
Phil

 

I just need to find one that goes down to 6 inch-lbs. THAT'S my problem.

 

So then do I simply rotate the engine to the proper position to set the injector and crank the adjuster in until I get 55 in/lbs?

 

Alright! Thanks for the help again, Stranger.

Phil

 

Hi everyone,

To continue flogging this topic...

I'm setting the injectors right now, and so far, the old injectors I have set, I have had to turn the adjuster in 1.25 turns before I get 55lb/ft. The one new injector I have set took 1.5 turns to get 55lb/ft.

When I am turning the adjusters in, the adjuster moves quite easily and then abruptly gets stiff and I get the torque value I need. Moreover, there isn't much adjustment left at all...I have the big lock nut backed off as far as it can go (until the threads start interfering with the flats on the adjuster nut head), and I only need to screw the lock nut in a turn and a bit before it tightens down.

Is the resistance I am getting on the adjuster nut the way it is supposed to be, or is this the same kind of resistance as you get when you stick a Q-tip in your ear? Am I going to wreck my injectors/bend the links the first time I try to start it, or was it just way out of adjustment before? Thanks again.

Phil

 

Thanks, my engine does have the VS notches, which I was able to figure out. However, the quote you produced isn't accurate in that you really can't set the valves AND injector on a single cylinder at the same time. For each VS notch for each cylinder (on the appropriate revolution for that cylinder) the injector needs to be set for a different cylinder.

I noticed that after setting the injector on 3 cylinders at the 55in/lbs, the engine seemed harder to turn over, which is what was making me wonder whether I'm bottoming the injectors

However, now that I have a benchmark for adjusting the injectors (i.e. the point at which the adjustment gets stiff) to work from, I can adjust them all equally, and since 2 of the old injectors were set exactly the same way, which was tighter than the new injectors, I think I'll just turn everything back to the 1.25 turns OUT from when the adjuster gets stiff.

This actually makes sense with my initial question about the 2 cylinders with the new injectors running colder and quieter at idle. If the new injectors weren't as tight as the old ones, then they would be running slightly retarded, which would make for cooler and quieter running. Hope it works...