Big Cam 3 Jake brake install

[JDirt]

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?

 

[mekanik]

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?

 

[59 North]

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.

 

[mekanik]

The NTA400 was a small cam it used the model 25 Jake Brake.
The big cam used the model 30 Jake Brake.

 

[JDirt]

The kit came with wider crossheads, in the installation instructions it says to reuse the locknuts off the old, non-jake crossheads.

 

[JDirt]

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.

 

[Truck Shop]

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.

 

[JDirt]

I don't remember a pin in the crosshead adjuster, I'll have to pull one back off and take a look

 

[Truck Shop]

The slave piston pushes on the pin which opens the the single exhaust valve.

 

[JDirt]

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?

 

[Truck Shop]

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

 

[Truck Shop]

pin would be longer than the hollow screw?

Correct-It should also be the same valve bridge/crosshead as the intake.

 

[JDirt]

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.

 

[JDirt]

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.

 

[Truck Shop]

So the truck is running, today we're going to drive it, try out the jakes

Good on you.

 

[JDirt]

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.

 

[Truck Shop]

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.

 

[oarwhat]

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.

 

[mekanik]

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.

 

[Truck Shop]

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