When rebuilding the engine in my dump truck, I decided to add jake brakes. 855 cummins cpl 625. Jake brake is 401b. I downloaded the installation manual and followed it to the letter. I got the jakes from a salvage yard, they seem to know about it, all the parts needed were in the bag. I first ran into a problem with the adjustment screw that goes in the injector rocker. It was too short, turns out there was a longer screw available and the guys at the salvage took care of it. Now I have the engine running and am ready to adjust the jake to exhaust valve clearance and these adjustment screws are also too short. This time neither the folks at Cummins nor the guys at the salvage know of any different screw. Looks like the problem is either the screw on top of the jake or the screw in the crosshead is too short. Anybody got any ideas?
My memory is fading. The 401 series Jake operated one exhaust valve through a pin in the adjusting screw in the exhaust valve bridge if I remember correctly. You replaced the bridge adjusting screw with the proper Jake part?
Whats the year on the engine? Don't know if it will help, just a thought as working from memory here, back in the mid '80's I worked with a 1975 truck that had an NTA 400 with Jakes, and for some reason I recall the NTA had a different number (25B?) for them, than on an NTC engine. I don't know if there is any difference or what it might be. Would have to research. Hopefully someone here can confirm or correct.
The NTA400 was a small cam it used the model 25 Jake Brake. The big cam used the model 30 Jake Brake.
The kit came with wider crossheads, in the installation instructions it says to reuse the locknuts off the old, non-jake crossheads.
I have a cummins/ jacobs application chart, it shows 3 different jakes compatible with my big cam 3, one of which is the 401b, it is in the column "original brake", also the instructions start out identifying compatible engines (dual volute turbo is one requirement for the 401b). I'm sure it's a compatible brake, talked to Cummins, they agreed.
First off the 401 series jakes-there are Zero-0-parts available. Second the 401B uses a dual entry turbo the 401C used a single entry turbo. The lash setting is .018 except for a few cpls like 796 which set at .021. The Kenworth outside salesman that calls on my shop just went through a exhausted search for rebuild kits for the 401 series. The exhaust bridge is the same as the intake bridge. The exhaust bridge adjusting screw that incorporates the single pin for jake is not available according to him. I had two that I gave him to help him out. I just got done going through a set of 401C jakes on a engine I just rebuilt. I was lucky and knew a place that had what I needed, the last they had. The updated jake to use is the 425 model.
I don't remember a pin in the crosshead adjuster, I'll have to pull one back off and take a look
The slave piston pushes on the pin which opens the the single exhaust valve.
Ok, I pulled a jake back off, there is a solid adjustment screw in the crosshead looks just like the one in the old non-jake crossheads. Am I right in that the one that should be there is hollow with a pin that goes through it? The pin would be longer than the hollow screw?
NTC---N=4 valve, T=turbo, C=custom rated, which is worthless. NTA------"------- T------"------ A=Aftercooled NTA400P=P industrial But with Cummins never stamp the same thing twice approach the engine tag could be stamped- NTC 400 BCIII or NTA 400 BCIII or NTA 855 BCIII HP 400
Correct-It should also be the same valve bridge/crosshead as the intake.
They sent me some wide crossheads with the jake hardware. I went back and read my installation manual again, looks like you're right, I should have reused the crossheads and replaced the adjustment screw, and reused the locknut. I did come up with a part # for that adjustment screw/pin assembly: 013555 I'll call the salvage back tomorrow, I hope they can find some of these.
I got the correct crossheads and adjustment screws, put it all back together over the weekend. Turned out I couldn't get the wider crossheads out because they hit the side of the rocker boxes. Had to pull the rocker boxes off, run the overhead again, I do everything the hard way. I bet I've barred that motor around 30 times. So the truck is running, today we're going to drive it, try out the jakes, check for leaks, put the hood back on, and hopefully put her back to work.
Good on you.
Truck runs and drives but has a miss, low power, called a friend who knows more than me, he came over and tracked down a dead #2 cylinder. Hopefully one of my new injectors is the culprit. The injector rocker adjuster won't take the slack out.
What procedure did you use to adjust the overheads {valves and injectors}. Did you set them starting A valves on #1 injector on #5 B valves on #5 injector on #3 and so on--or did you set valves and injectors at the same time on each cylinder? I would look at your injector push tubes to make sure none are bent, just a thought.
I'll second the idea of bent push tubes. Happened to one of ours as the young mechanic didn't know the procedure. His boss set it properly but it didn't run quite right. Two tubes were bent.
Sometimes when you lift the rocker housings off the push tubes lift out of the camfollower sockets. Look down there with a light and make sure there all in place.
Correct procedure for big cam. inj 6 inch lbs--valves intake .011 Exhaust .023 A valves #5-injector #3 B valves #3-injector #6 C valves #6-injector #2 A valves #2-injector #4 B valves #4-injector #1 C valves #1-injector #5
Yes, we checked for bent pushrods, ran the overhead as Truck Shop described, and made sure the pushrods were in their sockets. I sent the #2 injector back to Cummins, I should have another one tomorrow.
It has been years since I tuned a NTC series engine, but when doing the injectors, I always "exercised" the adjusting bolt. I would tighten it to 10-12 in/lbs and back off before doing the final setting. I would do it a couple times before the final set. My logic was that I was pushing any oil or other out of the threads to get the most accurate setting. Could have been nuts for doing it that way, but it made sense at the time.
I did/do the same.
I ran the injector screws down before final adjustment as well. So we exchanged the injector, the one in question must have had a broken spring or something, the plunger sat down about 3/8" lower than the new one. Truck starts easily and no miss. Today we hooked the trailer on, loaded the 953 and went for a drive. Seems about like 300 hp to me. Almost no smoke at all. Surely a fresh engine, new injectors, fresh fuel pump (supposedly built to cpl 625 + 15%) should be more powerful than the worn out turd it had before. Am I missing something?
Did you change cam/injector timing? Was it a 625 cpl to begin with? Does the turbo match the 625 cpl? Did you replace the fuel lines from tanks to pump plus return line?
Did not change timing or turbo, the tag says cpl 625, everything that came out of and went back in were the correct parts for a 625. When I sent the pump off, I gave them the engine info and told them I would like it to have a little more power, when it came back, I was told it was built to specs for that cpl (400 hp @2100 +15%) Surely at 460 hp it would make considerable smoke?
What type of fuel hoses are in it now? original? Is the return hose/fuel line braded hose? If it is remove the hose at engine and see if it is swollen inside. Check flow on return hose at tank.
The air fuel ratio control may be set too low. The adjustment is under the plate at the throttle shaft. You need boost to get fuel pressure and you need fuel pressure to get boost.
I talked to the shop that worked on the pump, he says stock settings for cpl 625 + 15%, with a #25 button. Also said I could change buttons if wanting more power, but should install a pyrometer with a #15. I was also wondering about turning the screw for more pre boost fuel.
Bend the plate and loosen the lock nut and turn the screw out 1/2 a turn to start. Go a 1/4 turn at a time if you need more.
A good pump shop/experienced will automatically set air fuel ratio 10% over the turbo lag. But most if told to set pump up 10% will only change fuel button. Yes it produces more smoke because of turbo lag but better throttle response.
We had an old Oshkosh snowplow with a rebuilt 350 Cummins. Just gutless. Adjusted the air fuel and wow what a difference. Don't go too far. It'll run like a raped ape and smoke like a chimney.