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Nhc250 valve injector overhead adjusting

WillWagner

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Just a bit of advice here. DO NOT use a screwdriver that has magnetic changeable bits. The bit will fall out and go down into the pan. The bit in the pan isn't an issue, the issue is that if the tool DOESN'T make it to the pan and gets lodged behind the cam follower lever. That will cause the cast iron housing to BREAK when the follower is pushed upwards by the cam. use a normal #3 flat blade screwdriver like this...I have one like this here at home and a Snap-On one like this but better at work.
A screwdriver adapter. Forgot, this isn't an N14. I will look for an image and put that up...my bad.

Here's a link,
https://store.snapon.com/Flat-Tip-S...lat-Tip-Standard-Industrial-3-8--P631912.aspx
 
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Zoidsfan77

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Mr. Wagner,
Just to help clarify in my own head. The injector actuation is pushed down or "closed" for most of the duration of the camshaft and the actuation is lifted or "raised" for the actual injection of fuel into the cylinder. I read your post a few times and that's my take-away but I want to be sure before I run the rack on my 250. It makes sense to me so far but I have another question. How does the injection system take the 170 to 200 psi of fuel and spray it at injection pressures required to make a diesel run? I always had it worked in my head that the injector was a "positive stroke" driven by the camshaft but instead, the camshaft holds it closed until injection is called for in this scenario. Help me understand. I think I need to go through mine as it smokes quite heavily at idle. Quite a bit can be attributed to the 50/50 centrifuge filtered waste ATF/Diesel mixture but I think a good overhead adjustment would give me piece of mind. My Deuce ran the same mixture and never smoked at idle but I am aware that it had a much higher compression ratio which would account for the cleaner burn of the fuel mixture.

Respectfully,

Joseph
I found this video a while ago that explains the Cummins PT fuel system. The video, along with Wills words of wisdom, helped me understand what is going on and how it works.

https://youtu.be/KzuwdxEJfQA

The short section about the AFC can be ignored, our non-turbo engines don't have one.

I highly recommend anyone looking to set their overhead whatch this video in its entirety. Hope it helps friend!
 

WillWagner

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Mr. Wagner,
Just to help clarify in my own head. The injector actuation is pushed down or "closed" for most of the duration of the camshaft and the actuation is lifted or "raised" for the actual injection of fuel into the cylinder. I read your post a few times and that's my take-away but I want to be sure before I run the rack on my 250. It makes sense to me so far but I have another question. How does the injection system take the 170 to 200 psi of fuel and spray it at injection pressures required to make a diesel run? I always had it worked in my head that the injector was a "positive stroke" driven by the camshaft but instead, the camshaft holds it closed until injection is called for in this scenario. Help me understand. I think I need to go through mine as it smokes quite heavily at idle. Quite a bit can be attributed to the 50/50 centrifuge filtered waste ATF/Diesel mixture but I think a good overhead adjustment would give me piece of mind. My Deuce ran the same mixture and never smoked at idle but I am aware that it had a much higher compression ratio which would account for the cleaner burn of the fuel mixture.

Respectfully,

Joseph
You are gonna have a hard time running the rack on your NHC, they don't have one, now a Detroit, they do. In a nutshell, positive END of injection is when the injector plunger is fully seated in the cup of the injector. if you watch the injector lever when you bar the engine over, the cam pushes the push tube up, this starts the nose of the injector lever downwards. When the lift of the cam stops the downward motion of the injector lever, that is the positive end of injection, or it is supposed to be IF is set correctly.

The PT system is not a pintle type system. When the rocker lever comes up, the cam on it's inner base circle, the low pressure fuel from the pump fills a chamber in the injector. As the cam starts pushing the lever down, transition to the outer base circle, a notch in the plunger is closed off and traps fuel around the plunger...this is for cooling, and in the cup. The plunger continues downward travel and forces the trapped fuel through 7 real small holes in the injector cup. This is the injection.

When you set the overhead...not a rack, each injector is controlled individually by a cam lobe and push tube, not by a common rack...you are torquing the positive end of injection seat between the plunger and cup in the injector. Too little torque or a gap will let combustion back into the injector cup and makes soot on the plunger resulting in poor high pressure injection. Too tight and you run out of physical space in the component stack up and will first break a crimp...the process that joins the top half and lower half of the plunger, and continued operation will wipe out a cam.

The deuce uses a Bosch system, a pintle type injection, meaning that it relies on spring tension in the injector to positively stop injection...the pump builds pressure, enough to overcome the tension of the pintle spring, un seat it, inject and then the pressure falls off allowing the pintle spring to force the pintle closed causing positive injection end. There is very low return flow, almost nothing. The NHC is a pressure timed system. Flow and pressure are increased with rpm, the fuel is used for cooling, lubrication and injection. There is LOTS more that goes on, but that' it n a short story.

Whew, that deserves a beer, it has been a while since I had to splain that. My fingers are tired.
If you need help or wana chat, PM me.

Oh yeah, Mr. Wagner is my Dad, He's passed. Me, I'm Will ;-)
 
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WillWagner

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That's funny, I ain't seen that video for ages! But I don't remember the dude having a Brit accent.

Don't go messing with the pump, IF you screw up, it can be expensive. But YOUR stuff ain't mine.
 

WillWagner

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I just watched this...This guy is confused. The injectors are NOT top stops, NEVER do IBC on these type.

Well, I guess you can do what you want, but what he said to do will cause issues.
 

Ajax MD

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Will,

How do we know if we have top stop injectors or another kind? Did the 809 series stick with a single type of injector throughout production or did it vary?
 

WillWagner

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Most had non-top stop. The way you can identify it is just like in the video above. You can see the spring. You can physically pull the spring and plunger out of the injector. A top stop injector has what looks like a giant 12-point nut on the top of it and the only thing you can pull out of the injector is the link. The link is a small push tube that's got like a mushroom top on it. Non-top stop links are about 5 inches long, tops stops or about 4. Thier is not much of the injectors sticking up out of the head for non top stop, top stop injectors stick out of the head about an inch and a half
 

m925a1dmax

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So I have the top stop injectors. Am I gonna adjust the injectors using 6in lb or 68-72 In lbs.

Also do the top stop injectors have tip gaskets. I haven’t been able to find any so I’m assuming not.


Sent from my iPhone using Tapatalk
 

simp5782

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So I have the top stop injectors. Am I gonna adjust the injectors using 6in lb or 68-72 In lbs.

Also do the top stop injectors have tip gaskets. I haven’t been able to find any so I’m assuming not.


Sent from my iPhone using Tapatalk
No.

Top stops are 6 in lbs
 

WillWagner

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Correct Simp, but do NOT do valves and injectors on the same cylinder. A= I-3, V-5, In .011, ex, .023
 

Jcoffman84

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There are two ways to set the overhead on an 855. One is the outer base method and the other is the inner base method. The inner base method can ONLY be used on top stop style injectors. The accessory drive pulley is marked differently for the IB method, TDC1-6, A, B, C.
Most of the NHC's that I have seen are marked TDC1-6, VS1-6, 2-5, 3-4. That is used for OB method.

A little schooling first. The base timing for the engine is done by aligning marks on the crank and cam gears. The injection timing is done with shims under the cam boxes by measuring the positive end of injection, (or beginning, I've had instructors tell me both), when the piston is at .203 BTDC. The pumps don't need timing on these, but, the part that drives the pump does. That would be the accessory drive. The accessory drive can be removed and put back into an engine that runs fine w/o timing it to the cam. Nothing physically changes when that happens, it will run the same, however, the next time that someone needs to go into the overhead, they'll be screwed. The pulley that has the marks on it for the overhead set is pressed onto the shaft that needs to be timed to the base engine..the accessory drive shaft.

On an engine that uses top stop injectors, (top stops have a barrel and jamb nut that sets the travel of the injector to match the cam's outer base circle, you can't see the spring on these injectors), an easy way to check to see if the accessory drive is in time is to align the pointer and A on the pulley. The overhead set for top stops goes like this;
I V
A 3 5
B 6 3
C 2 6
A 4 2
B 1 4
C 5 1

Hang an overhead wrench on Injector 5, and bar the engine over while watching the wrench, don't watch the pulley. When the wrench starts to move, ramping up to the OBC on the cam, STOP. Look at the mark. It should be within a 1/2 inch of the pointer...either way...the acc drive is in time, GTG with setting the overhead.

On an engine that uses non top stops, you can check this from the get go, but not as you go through the tune up steps if the engine has been apart. Non top stop injectors have no barrel and jamb nut to set the travel. That's why the overhead set is different. The injector is set on the outer base of the to a specified torque sufficient enough to load the push tube and seat the plunger so the compression in the cylinder won't go back into the injector after positive injection ends. It also plays with injection timing. A loose setting and injection starts later, (slow timing), and a tighter setting starts injection sooner, (fast timing). The same can be done when setting top stops, NO performance gains can be made here. If you wanna mess around with timing for power, smoke, etc. it needs to be done at the cam boxes. The only thing a loose setting does is carbon plungers and tight...too tight... of a setting bends push tubes. Back to acc drive timing. The OBC of the cam is roughly 60% of the lobe, so when the pointer and VS1-6 are aligned, the injector lever for 1 might very well be down, but you have no idea where it is in that 60% of OBC. When any of you attempt to do anything in the overhead, use the above outlined method of checking the timing BEFORE you start disassembling things. If for some reason it isn't in time, PM, e-mail or call me and I can walk you through re marking the pulley.

The overhead set on the NHC for the OBC method goes like this;

A 1 or 6
B 2 or 5
C 3 or 4

Set the valves and injector on the same cylinder, in firing order, setting the injector first to load the rocker shaft,

We'll start with A being cylinder 1 and first in firing order. The injector lever should be down, the nose of the lever pushed down toward the injector. Both valves need to be loose. You can use a click or dial type torque wrench, just make sure it is a known good wrench. The screw shouldn't move much if you are just tuning up, but, if the engine has been apart or you put another injector in it, the screw and injector lever will move quite a bit. You will need to torque the injector screw to 68-72 INCH pounds. That isn't much, but the injector spring tension will be overcome by it and, again, if the engine has been apart, the plunger and nose of the injector lever will be pushed down into the injector, that is what you want, remember you are setting the injector on the outer base circle of the cam..in it's farthest downward position. Lock the jamb nut down...IIRC 40 ft lb and move on o the valves. .014 intake, .027 exhaust. The cross heads are adjustable also, but we'll keave that for another time. Bar the engine over to the next mark, VS2-5, 2-5, sometimes they are marked different, and go through the steps again. 68 to 72 INCH pounds on the injector and .014 and .027 on the valves. Bar it again and repeat. If for any reason it gets hard to bar over...other than trying to overcome the engine compression STOP, something isn't kosher. Loosen things up, regroup and start over. You'll know if the difficulty in barring is from compression if it gets hard and you stop and wait a few seconds and you can continue on and it's easier. You'll also hear a "hissing" noise coming up through the push tube cavities as each piston is brought to TDC on the compression stroke.

I'll see if I can dig up some books with pics, scan them and put them up in the 5T section. I'd make a vid of it but I don't see this stuff at work any more. If anyone by me wants to do a tune up, we could do one here, go through the motions on R&I ing an injector, checking timing and tuning up and put it on digital so it can be posted here as a sticky.

Hope that doesn't confuse anyone. If you need help, you know how to find me. :beer:
Did you ever find those pics to post? I’m about to attempt this with my truck.
 

WillWagner

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Nope, that stuff faded away faster than milk writing on parchment. Easy enough, pull the lids and determine what injector you have....the data plate on the accessory drive ear should tell you if it is still there....then just follow the above for which injector you have. If when you look down at the injector and see a spring, non top stop. If all you see is the link going into the top of the injector, top stop. Top stop, injector on 3, valve on 5 when on A. Non top stop, make sure both valves are loose on 1 or 6 when A or VS 1-6 and the injector is down, adjust the injector 1st using the torque method then the valves on the same cylinder.

A tip, if it doesn't need it, don't mess with it. Smoke will be your clue. white smoke at idle/low load, black smoke loaded means an overhead set is in order. And, If the thing has been running loose, you can make way low power after an overhead set. Carbon on the plunger will be forced into the injector cup and plug the holes.

68 -72 INCH lbs! Ft lbs will f things right on up!

Continue on....
 

Jcoffman84

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Nope, that stuff faded away faster than milk writing on parchment. Easy enough, pull the lids and determine what injector you have....the data plate on the accessory drive ear should tell you if it is still there....then just follow the above for which injector you have. If when you look down at the injector and see a spring, non top stop. If all you see is the link going into the top of the injector, top stop. Top stop, injector on 3, valve on 5 when on A. Non top stop, make sure both valves are loose on 1 or 6 when A or VS 1-6 and the injector is down, adjust the injector 1st using the torque method then the valves on the same cylinder.

A tip, if it doesn't need it, don't mess with it. Smoke will be your clue. white smoke at idle/low load, black smoke loaded means an overhead set is in order. And, If the thing has been running loose, you can make way low power after an overhead set. Carbon on the plunger will be forced into the injector cup and plug the holes.

68 -72 INCH lbs! Ft lbs will f things right on up!

Continue on....
Well it doesn’t have any smoke coming out of the stack at all. I just don’t know when the last time was that it’s been done so I was thinking about doing one on it. Local shop said minimum $500.00 to do an overhead
 

WillWagner

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And, as to the typewriter comment above, MOST of the time it is the crosshead that makes the noise. I do not believe that I have covered the adjustment of those because it is a feel/visual thing. Maybe one day I can do a video of how to set them up and/or adjust them.
 

msgjd

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There are two ways to set the overhead on an 855.... A little schooling first.....
WillWagner, that detailed post of yours from 07aug11 is irreplaceable.. Using it and the TM, I was able to do the overhead in less than a day. This included a lot of study time the same day, never done a 855 cummins before.. The TM is tricky and as someone mentioned, one of the charts is incorrect... I also noticed within a certain awkward part of the TM's wording structure, it is easy for someone to use the wrong torque specs. The paragraph starts out with setting non-top stops and then throws top stops in there, it jumps around a bit with that curve ball.. Perhaps that is why one of my "direct from the army" M818's had only 5 inch-pounds on it's non-top stops instead of the 72 the TM calls for .. A #6 skip brought me to the task, and discovered a clogged injector inlet screen. Some OMS yoyo in PA used teflon tape on the post-PT fuel line to the head... TM does not say, but things go a lot better with the power steering pump moved out of the way, especially when the accessory drive pulley marks are heavily painted .. Had to sand much of it down to find the notches and numbers. Luckily, the Acc Drive was in register with the rest of the engine .. Thanks for the tidbit about checking the register first, since the manual says nothing of the sort as you know, Truck runs like a top now. Thanks again
 
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WillWagner

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Thank you. Many moons ago, on Saturdays, a guy I worked with and myself would go out to a warehouse in Santa Fe Springs and do nothing but tune ups. $150 w/o jakes, $200 with. We would average 24 overhead sets for the day, unless the majority were cab overs. Right around 30 mins w/o brakes and 40 with., again, unless it was a CO. We did no advertizing, they just showed up. That was some easy and good money for the less than a day work. It was fun!

Teflon tape has no place in a fuel system just for that reason. Teflon sealant is ok, but it is not fuel resistant and can leak. Permatex #1 works best, dries hard, won't drip/sag when it gets hot and is fuel resistant
 
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