Cummins NHC 250 with dead cylinder...need some experts on the old engines

I just picked up a new liner, piston, wrist pin, gasket kit and rings today. Injectors should be in by friday.

This engine has no sneezers or turbo...less to go wrong, I suppose. The piston was the opposite of seized...it just pushed right out, it was so worn.

If I can figure out a setup to get the old liner out, getting back in business shouldn't be a big deal.

Does anyone know what torque my connecting rod bolts should be?

Is there some way to bleed the fuel system on this engine once I get it back together, or does it look after that itself?

How careful should I be for break-in with an engine that is only 1/6 rebuilt, and only the cylinder and piston at that (no bearings)?

 

Oh yeah, what clearance to I adjust the pushrods for the valves and injector to? Thanks.

Phil

 

Well that is interesting. I can't see any wear on the cam or follower...they both appear to be in excellent condition. Clearly, I had a bad injector as evidenced by the localization of the erosion of my piston.

The guy at the parts place wondered if my engine had been dusted; all the scuffing of the piston. It probably has, but the dark areas on the bottom of the skirt indicate that the heat damage to the piston was likely from hot combustion gases flowing down around the piston.

This old thing won't put on 100hrs a year, I hope it will last a couple of years.

BTW, these are aftermarket parts I got...Cummins (via. my local Navistar dealer) said they would only sell me complete inframe kit since they didn't know whether my engine had original pistons.

The parts store guy seemed reasonably sure that what they brought in was equivalent to what I took out. Time will tell. For $350 vs. $2200 I'll risk it this time. Maybe I'll learn somthing. I'll keep you all posted.

 

Hi there, seeding is done and I can finally get back to work on the truck. All the big stuff is done, and I'm trying to adjust the valves and injectors. I'm using a book for a Big Cam IV, most of which seems the same, but I can't find anything pertinent for adjusting these old style injectors.

The only procedures in the book are for "top stop" injectors and "STC" injectors. I'm positive I don't have STC, and I'm quite certain that I don't have top stop. How do I adjust the injectors? At the top of the injector there is just a spring with a metal cap through which the link protrudes.

Do I just adjust the injector for zero clearance, or do I need to preload the spring with some kind of tiny torque wrench? Thanks for the help.

Phil

 

I think what you are referring to is the procedure to check for leaking injector seals. You bottom the injector plungers and torque to 60lb/in then put the air gun on the fuel inlet at the rear head and pressurize the fuel gallery to 30psi then look for air bubbles up the injector sides.

I don't think much changed on Cummins engines from 1950 to about 1994.

You have to set the valves on one cylinder while setting the injector on another. And after you're done, you must check the injector settings on cylinders 2,3 and 5 (I think) to "account for any camshaft deflection that happened during the setting sequence."

If you have an old book, I'm sure it will say the correct way, and it isn't that difficult. I have the setting marks all figured out on my accessory drive pulley, I just don't know what to do with the adjusting screw

Thanks,

Phil