NHC 250 Valve adjustment problem

I've read the sticky on this, and following that got 3 of the cylinders adjusted easily. My problem is when trying to adjust cylinder 3. I have the pulley in the correct spot, and know I'm on cylinder 3 to adjust, but the exhaust rocker has no play. I've taken the adjustment screw completely out of the rocker and there is still pressure on the rocker. I'm wondering if I need to adjust the crosshead to get things working properly. Any help appreciated.

Backstory: Always had trouble starting this engine and one year in the fall I tried and could not get it to go (I think a fuel issue is the cause of the poor starting). I left it for about 9 months before trying again and the engine was stuck. I left it that way for about 5 years, and last year I pulled the rocker boxes and injectors, added some atf and got it spinning nicely. I got everything back together and just need to set the valves and injectors to button the engine back up. I did pull all of the push tubes, but numbered them and got them back in the same spot they came out of. Rocker boxes are all back on the same cylinders they came off of as well.

Accessory drive timing could be off, could have a beat in seat or a dropped seat. With the adjuster back in the lever, are there about the same amount of threads sticking out of the exhaust as the intake when the lever touches the cross head? If you remove the cross head, is one valve higher than the other...on the exhaust.

WillWagner said:

Accessory drive timing could be off, could have a beat in seat or a dropped seat. With the adjuster back in the lever, are there about the same amount of threads sticking out of the exhaust as the intake when the lever touches the cross head? If you remove the cross head, is one valve higher than the other...on the exhaust.

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I was thinking the accessory drive timing was correct as I was able to adjust 3 other cylinders just fine. I also watched the #3 exhaust rocker and at it's highest point of travel there is still no slack. Not quite sure what you mean about the threads sticking out of the lever.

I too was concerned about possibly having a beat in valve seat, I sure hope not. I will try to remove the crosshead when I get back to the truck, and see if the valves look about the same height, but that won't be for about a week and a half.

I may just have to loosen up the rocker box and get the push tube back out and adjust the crosshead per the TM. If I still have problems, I'm not sure what it could be other than a messed up exhaust valve/seat.

How to check accessory drive timing. When you can go through 1/2 of the tune up process and the engine locks up, it usually means the timing is off or you have done it incorrectly.

Top Stop, Adjust A, Inj 3, Valve 5. Put a socket with a 6 inch or so extension on it on the #3 injector jamb nut. Bar the engine and watch the extension. When you see it start to break....start moving to the exhaust side of the engine...stop. Look and see where the mark on the accessory drive pulley is from the pointer on the cover. It should be within an inch or so from the pointer.

Non top stop, adjust or set the pointer at A, easier to do A 1-6. Put the socket/extension on inj 5 jamb nut and bar the engine while watching the socket. When it stops moving, you should be close to the pointer like above.

OP, if when the engine ran last, you heard no popping in the intake...air filter, or out the tail pipe, 90% no dropped valve, BUT, a WAY out of adjustment cross head can sound like a seat issue. Be careful adjusting cross heads, if you do it wrong, it can lead to a dropped valve or worse.

I had a similar if not the exact same issue with a rebuilt by someone 250 we used to repower a M4 high speed tractor. It was hard starting so we replaced the pump which fixed the starting problem. We then pulled the injectors and had them tested and maybe rebuilt, I can’t remember. When we went to set the rack the same thing happened. We couldn’t adjust it past the 3rd cylinder. It turned out it was the procedure we were using that was the problem. It has been quite some time so I cant recall the adjustment procedures we tried and finally used but I do recall that there were a couple ways to adjust it depending on the rack or injector setup you have and different index marks to use. the instructions I had didn’t give a good enough step by step for me so I was missing a something and ended up stumped where you are now. We ended getting a mechanic to come out and show us how to setup the rack. The problem ended up being we weren’t setting the rack on the right part of the cycle. Hope this helps.

There's your issue, Cummins has no rack!

WillWagner said:

How to check accessory drive timing. When you can go through 1/2 of the tune up process and the engine locks up, it usually means the timing is off or you have done it incorrectly.

Top Stop, Adjust A, Inj 3, Valve 5. Put a socket with a 6 inch or so extension on it on the #3 injector jamb nut. Bar the engine and watch the extension. When you see it start to break....start moving to the exhaust side of the engine...stop. Look and see where the mark on the accessory drive pulley is from the pointer on the cover. It should be within an inch or so from the pointer.

Non top stop, adjust or set the pointer at A, easier to do A 1-6. Put the socket/extension on inj 5 jamb nut and bar the engine while watching the socket. When it stops moving, you should be close to the pointer like above.

OP, if when the engine ran last, you heard no popping in the intake...air filter, or out the tail pipe, 90% no dropped valve, BUT, a WAY out of adjustment cross head can sound like a seat issue. Be careful adjusting cross heads, if you do it wrong, it can lead to a dropped valve or worse.

Click to expand...

I will double check the timing before going further, but I can turn it over 360 degrees and my #3 exh. lever is still pushed tight against the push tube w/o the adjuster in, so something else is still off. Don't recall any bad noises when it ran last, but it was so long ago who knows.

Threads sticking out of the lever. Normally there should be 2 to 3 threads protruding past the jamb nut. One valve, In or Ex, I forget which one, does have more protruding than the other, but all cylinders will be the same. If you have one cylinder with 5, 6, 8 threads on the adjusting screw protruding past the nut, there is an issue there. If something got dropped down the push tube cavity and landed in the follower cup, it will give you the result you have on the cylinder with the push tube tight against the lever. If you had the push tubes and or rocker boxes off and when you went back together, a valve and inj PT could have gotten mixed up, injector is longer IIRC, the PT could have jumped out of the socket on the follower and is sitting between the valve and inj followers...not in the cup. I'd pull the box and have a look see.

Well, the fix was actually quite simple. The #3 exhaust push tube came out of the lifter cup. What had me stumped was that the rocker moved when rotating the engine before. This was due to the push tube touching the camshaft lobe. Hopefully the cam is still fine. Got everything adjusted. Next time up will try to put some fuel to it and see if it fires.