Nhc250 valve injector overhead adjusting

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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-Standard-industrial-3-8-quot--Socket-Driver-Flat-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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Mayo, MD
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

I'm the dude, man!
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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
 
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