XM817/NHC250 Valve adjustment

[mckeeranger]

I’m going to be replacing the injector seals and adjusting the valves in the XM817. It has the Cummins NHC250, normally aspirated. I have only found one other post about it, 8/5/2005, but there was no real information or pictures.

If anyone is interested in seeing it, I'll post pictures. If I get it right, you will get to see what is involved in the job. If I get it wrong, and toast the engine, you will get to see what is involved in the job, and get to see a grown man cry.

Either way, it should be informational.

 

[98hd]

I’m going to be replacing the injector seals and adjusting the valves in the XM817. It has the Cummins NHC250, normally aspirated. I have only found one other post about it, 8/5/2005, but there was no real information or pictures.

If anyone is interested in seeing it, I'll post pictures. If I get it right, you will get to see what is involved in the job. If I get it wrong, and toast the engine, you will get to see what is involved in the job, and get to see a grown man cry.

Either way, it should be informational.

Please post up when you do, I was thinking about doing mine eventually.

 

[Pappa-G]

When I did my valves I closely followed the steps laid out in TM 9-2320-260-34-1 Task 3-38 on page 3-244. E-Z, just take your time and don't put your toe through your radiator. When you get finished with the adjusting roll the crank around twice (with the fuel OFF) by hand making sure nothing binds up. Good Luck

 

[jwaller]

I paid $70 to my local big truck shop not to have to mess it that chore. best 4 I ever spent.

 

[dozer1]

Reviving a thread here. I couldnt have entitled one much better. XM817/NHC250 Valve adjustment . OK here goes. First off I know how to read the TM. The problem is there is a difference between how the TM tells you to set the crossheads and how a lifelong Cummins mechanic that I know has always done it. The TM says to turn the adjusting screw until it touches the stem, then go .020 - .040 more as measured with a dial indicator, then tighten the jamnut. TM 9-2320-260-34-1 PAGE 198 section 3. The mechanic says to turn the screw in until it touches the valve stem, then tighten the jamnut. No need to go that extra .020-.040, His civilian Cummins manual backs his method. His method makes sense. You would want both those valves opening at once and the same amount right? SOMEBODY PLEASE EXPLAIN TO ME HERE WHY I SHOULD BELIEVE THE ALMIGHTY TM HERE. Mechanic has no Idea why you wouldnt want them even. I dont either. Any comments?

 

[dozer1]

TM 9-2320-260-34-1​

3-63. CROSSHEAD INSTALLATION
THIS TASK COVERS:
Installation
INITIAL SETUP
APPLICABLE MODELS MATERIALS/PARTS​

All Lubricating oil (Appendix C, Item 21)​

TOOLS REFERENCES (TM)​

General mechanic’s tool kit
(Appendix B, Item 1)
TM 9-2320-260-34 P-1
Torque wrench, 3/8-in. dr.
(Appendix B, Item 4)
Dial indicator (Appendix B, Item 11)
Wire gage (Appendix B, Item 94)​

Installation​

Loosen adjusting screw (2) one full turn.
Install crosshead (3) on guide (5) so crosshead (3) touches valve stem (4) on side opposite adjusting
screw (2).
Turn adjusting screw (2) until it touches valve stem (6).
Position dial indicator over center of crosshead (3). Zero dial indicator.
Holding crosshead (3) down lightly, turn adjusting screw (2) until dial indicator reads 0.020-0.040 in.
(0.51-1.0 mm). Tighten jamnut (1) 22-26 lb-ft (30-35 N•m).
Using wire gage, measure gap (7). Measurement must be a minimum of 0.025 in. (0.64 mm). Loosen
jamnut (1) and turn adjusting screw (2) clockwise. Tighten jamnut (1) 22-26 lb-ft (30-35 N•m).
Repeat step 6 until gap (7) is correct.​

Remove dial indicator from cylinder head (.

 

[mckeeranger]

I think the reason for this procedure is to ensure the crosshead is perfectly vertical on the crosshead guide. Especially on a worn engine, the crosshead could be slightly racked at contact with the second valve stem, resulting in binding and/or uneven wear between it and the guide. By making this adjustment, you are "leveling" the crosshead and making it "plumb" with it's guide. I'm sure the "0.020-0.040 in." in the TM is based on the clearance between the crosshead bore, and the crosshead guide diameter.

I realize there is not much play between the crosshead and guide, but these are precision parts where thousandths of an inch can make a difference. With this in mind, I would follow the TM.

The only reason I can see for a discrepancy between the TM and civilian book, would be they figured out it's not that big a deal.

I think a better question would be how step 5, adjusting the gap using a dial indicator, is still accurate if step 6 is making an adjustment to the same gap (if necessary) with a feeler gauge?

On another note: I apologize for not posting the promised pictures, the camera battery died.

 

[dozer1]

I think a better question would be how step 5, adjusting the gap using a dial indicator, is still accurate if step 6 is making an adjustment to the same gap (if necessary) with a feeler gauge?

That indeed could be a great question but I havent stumbled upon it yet, as I am awating many internal engine parts before I can install the heads and set the valves. At this point I got my heads back from the shop and just figured I would set the crossheads up in them on the bench. I did it as the TM says and went a step further. I went with .028-.030 for a range as it is in the middle of there rather broad range. Thanks for your input on setting the valves. My cummins mech insists on using the torque method of adjusting the valves as he has done hundreds of engines that way. He is the one who wants to know why they want you to screw in that adjuster an extra 20 to 40 thousanths. He cant imagine why you wouldnt want them to open at the same time and the same amount. Thats alot in precision measuring terms. Dean

 

[WillWagner]

You mean torque method on the injectors. The reason behind going the extra .020 or so is that on a used engine all the parts wear, x-head guide, x-head, valve stems, x-head adjuster screw. The amount given is incorrect in my opinion because the stuff doesn't wear uniformly. The way to set a cross head is actually by feel and to watch what it does during the adjusting process. Kinda hard to describe. Put pressure on the center of the guide with your thumb if on the bench or with an un adjusted and loosened valve lever and downward pressure on an assembled engine. Loosen the x-head jamb nut, back it off 2 or 3 truns and back the screw out. With pressure applied to the x-head as described above, gently turn the x-head adjuster in until you feel it touch the valve stem, then, with a bit more force, and keeping pressure on the x-head, continue turning the screw in and watch the x-head. You will see the x-head spin to the right and feel the adjuster come to a positive stop. Keep pressure on the x-hard with the lever or your thumb, spin the jamb nut down and snug it with a wrench. Then adjust the valve. Do the injector adjustment first...it loads the rocker shaft..then the valves. From a running engine back to a running engine, maybe a half hour...w/o engine brakes.

 

[dozer1]

You mean torque method on the injectors
right on
thanks mckeeranger and willwagner for those answers. I have to go along with the "wear compensation" answer. I went on to read the section of the TM "injector and valve adjusting torque method" and they adjust the x-head there without the extra .030 or so. For my application, that is what I am going to do as the engine was new in '85 and only saw 2029 miles. Very little wear, just was stuck in the cyl's from sitting.

 

[Floridianson]

and get to see a grown man cry.[/COLOR].

Sorry your so far away I would let you use my dial set up for these motors I got from GL. I do not use the TM's for this but use the instructions that came with the tools. I feel the dial set up is the only way to go but you need more than just a dial indacator you need the hard wear that allows you to hook and pull all the slop out of the system to get the correct reading on the dial.