JoeH

Just to clarify, is it a Mack Dynatard or a Jacobs engine brake? I'm not familiar with the solenoids of either one, but I believe they're fairly different. Good news on the valve lash check. Generally a failing exhaust gasket will have a chirping sound. There's 6 individual gaskets, and to replace you can loosen all the studs and take off the manifold/turbo assembly or if you're by yourself and can't lift that much weight you can leave a couple nuts on and cut notches in the new gasket bolt holes so you can drop them in from the top. If one is leaking you'll have black soot around it, and with engine running you'll feel air puffing there. Our e7 exhaust manifold rusted the mating surface on #6 and hydrolocked, fortunately didnt break anything, had to take the manifold off go weld/grind it back up. Our '79 endt676 over the years always needed the exhaust manifold nuts tightened periodically, and one time broke a stud! Annoying, but it the threads in the head spun right out by using a broken drill bit spinning backwards. I may have had to center punch it in a few places to give it some texture for the bit to grab. I also have a steel dash R model with a 237 endt675 that has a head gasket that's been chirping for maybe 10 years? Its a truck that gets used about 3 times a year here at the yard.

My dad times the old ENDT676 motors with a snow plow pump. Helped him do it once a few years ago, dont know what the process is for the E7. Fill the plow pump with diesel, hook it up to the injection pump. I think the plow pump relief valve needs to be set to around 700psi. The book says to use some special pump to do this process, so he just used a plow pump because that's what he had.

Took me a few minutes to remember the systems name: Puff Limiter.

Doubt anyone set up the pump, the fuel pump has a slave cylinder that governs fuel until intake pressure from the turbo jumps. It is tied into an aneroid? valve on top of the intake manifold on the rear head. These fail and get deleted, resulting in full access to fuel regardless of boost pressure. Rolls coal til the turbo catches up then it clears right up. On this engine the pyrometer should say Downshift at 1125° so you're fine at 1100. If it keeps pushing passed 1125 then change your air filters. This engine setup uses 2.

Don't think so. This spare is a 1981 endt676, same year and engine he's working on.

Pairs on the damper are 1-6, 5-2, 3-4. In 2 rotations you'll hit the whole pattern in order. I'm hoping your spare engine can donate a timing pointer.

Had to take a screenshot of the picture to get it to load.... You can barely make out a 4 | 3etched in where the yellow marker is. That's what you're looking for on the damper wheel. The firing order 1-5-3-6-2-4 is cast into the block above the rear tappet cover.

We mark our engine dampers with yellow marker 1 | 6 , etc, where the | marks that the pair is at TDC. Each pair is 120° (1/3) apart from the next pair. You check the valve clearances in the firing order. If you get one rocker that's got too much Freeplay then you need to pull the pan and check that lifter. All it costs you is an oil pan gasket and an oil change to pull the pan. No you cannot see the cam from the tappet covers. Valve covers (which are a nightmare of plumbing to remove) and oil pan. For reinstalling valve covers, do it BY THE BOOK! Dry, no silicone, no gasket adhesive. DO NOT overtorque valve cover bolts, it makes the sides flare out, and you'll have leaking valve cover gaskets.

The marks on the damper wheel are etched in, you have to wire brush it to see them. Pointer should be on the timing cover, around a 10 o'clock position as viewed from front of vehicle.

Sounds like you have a bent pushrod. I'd be checking valve lash on everyone. Common problem on these engines is the carbide faces on the lifters breaking and then what remains shaves the lobe right off the camshaft. Berry Cams I think can weld and grind a new lobe onto the cam for you if you don't have a spare cam. You'd have to come up with a new lifter tappet, and replace the bad pushrod. Truck could have weak valve springs that allowed the pushrod to come loose and get bent in a high rev situation. I'd drop ol pan, look for tappet face it there and get eyeballs on the cam from underneath. Valve covers and oil pans show you a lot of what's going on in there.

Sideways torque arm? Rubber doesn't have as much resistance to keep spring packs straight, so your axles will tend to wander more. We have a truck with 38k rubber bushed camelback and the tires will wander as much as 6 inches out of alignment backing up in turns. Truck doesn't take long to hit this point after putting new bushings in.

Gas engines have valve seals because when you slam the carb shut it creates vacuum pressure that can suck oil down passed through the valve guide. Diesels are fully open intake all the time, so no jump on vacuum pressure when you get off throttle. People more familiar with these engines can chime in, but it's my understanding diesels don't really need valve seals.

Did the truck have wedge brakes originally?

Lol I was reading service upside down, it looked blurry to me. Somehow I got DOT AV30 out of it... I'm going to take another stab and say Holding Valve.

Looks like it says DOT AV30 on it, so google provides an air volume control. Where was it mounted? Did it have lines going anywhere? What was this truck before?

Tractor protection valve?...

We bought a 1/4 cow last year and put it in a chest freezer. Was about $5/lb hanging weight, we dealt with the farmer who worked with a local butcher. Ground beef at the grocery store is cheaper, but where you save the money is on the roasts and steaks. Local small butcher shops I expect could put you in touch with a local farmer, but maybe the butcher environment is a little different here in PA.

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Our 79 r686 has about 6 inches of wander. It can get bad enough the slack adjusters can hit the frame rails...

There should be a sideways torque arm from the right frame rail to the rear differential. The eyes on these wear out, but if the truck is acting this way from new I'd wonder if someone forgot to install it... Reread, you stated it's missing the transverse torque arm. There's your culprit. I assume all your other trucks have it. For shits, go to your dealer parts dept, and run the trucks VIN and ask for that torque arm. If it comes up as a part on the truck then I'd tell the dealer to file a warranty claim and install it on Macks dime, citing that it never had it from new so they must have forgotten it at the factory.

You'd blow up the motor at 14,000 rpm! Change your fuel filters (2 I expect) when they clog they become a restriction point and act like a governor.

I think you're overthinking it. Its thin wall metal, and gets softer the more you heat it up. I'd think the pipe would give before anything else. My '79 endt676 is rigid pipe off turbo, down along transmission, and below frame. It then has flex pipe before heading to the muffler. Pyro says downshift at 1125 degrees, and it's factory rigid.

Its not an expansion joint, it's a flex pipe. You're fine on rigid pipe until you make the transition to the frame mounted muffler stand. That transition will need to be flex pipe. Never used the bellows type. The engine and transmission can rock sideways in the frame a good bit under load. Especially if your transmission bolts work loose.... 🙄

Heck, I'd be fertilizing my pants on those inclines! My truck runs a V box type body that is about 11'6" overall height at 73,280 lbs so I get nervous at any kind of angle.

Drove a Peterbilt once that had an air piston to raise/lower the passenger window via a switch on the dash. I thought that was slick. Driver side was hand crank. On those steep inclines I'd be a bit nervous on light springs. I'd want heavy springs to a) create less lean angle between frame and wheel alignment, and b) more safety factor to offset overload fatigue on the downhill side.