steve s.

Your engine is an EN 377. Serial number 4365.  Bore and stroke 4"x5", 377 cubic inches.  Almost all Mack gas engines of that era called for a point gap of .022", you're real close. Are you looking for any specific information?  With any old truck that has been sitting for some time, you have to suspect some crap in the fuel system will cause you trouble. But in the other hand, it could be any number of things making it run rough. Good luck.

Air ride would be nice, but it will cost more, take more time, and never look like it belongs under your B model. The choice is yours, but if you want to save time and money while keeping your truck looking original, just go to a spring shop and buy the leaf (leaves) that you need.  I needed a main leaf for a 56 H model, and the spring shop had one on the shelf !

VIN numbers did not exist before 1969. Your truck has a serial number. That is the number you will need to use when asked for a VIN. The number should be on a plate at the lower side of the passenger door. It is also stamped into the frame near the rear spring hanger for the right front wheel.

I have a very nice driver side 3 hinge door . It is either NOS or completely restored.  I also have an NOS 2 hinge door skin for the passenger side if that would help you. It could easily be adapted for 3 hinges. Steve

If John Chalmers is not able to help, here is another possibility: When I overhauled my 673 engine, no "set" of piston rings could be found. The Mack service manual had specs on each of the ring sizes and types. I took that information to a Hastings website and ordered the rings individually to make my own set. The price was very reasonable, in fact it was a bargain. Like so many things you encounter with an old truck, you sometimes have to be creative to get the parts you need. They are usually out there somewhere. Might be worth a try.  Steve

If you added a transmission  with a .75 overdrive, and changed nothing else, you could run 60mph at just under 2100 RPM. Simple.

You have a 4 speed transmission with fourth gear direct. Changing to a transmission with a fifth gear that is overdrive would be a good way to gain road speed. Changing your tires to 10.00x20 (or radial equivalent) would gain you a bit more. I am not familiar with the CR25 single reduction rear axle, but it is quite possible that another series of differential might fit in your axle housing, giving you more gear ratio options. Start with the 5 speed.

The 4 things that affect road speed are engine speed, transmission ratio, rear axle ratio, and tire size. You can't do much about your maximum engine speed. Does your transmission have overdrive? If not you could change to a transmission that does, or you could add an auxiliary trans that has an overdrive ratio. You can probably find a faster gear ratio for your rear axle, or change the whole axle to something with a faster ratio. The larger the diameter of the tire you run, the higher your road speed will be, but the change won't be great.  So, what transmission and which rear axle  do you have? They are probably your easiest places to make an improvement.

I had a B61 with the engine tilted to the ditch side. It was not the original engine . I have no idea why someone did that, but it was a pain in the neck to work on at times. In order to pull the back cylinder head, I had to drill a hole in the firewall to remove the last push rod. Trying to use a torque wrench at that odd angle from underneath was awkward to say the least. The engine must have come originally in an MB or some other cab over, as the engine number is on the back of the block, under the cylinder head. 

I took the engine out, changed the flywheel housing and water pump housing, and put it in a different B61 standing straight up. I like it much better this way.

Julie, thank you for telling us about your father. I have been following his posts here for years. He always added something of value to the conversation, and there was no doubt that he knew what he was talking about. He spoke with an authority that only time and experience can give. I am thankful that folks like your father take the time to share their knowledge with the rest of us. We will miss him around here.

Here are a couple pictures to help clarify things. The red truck has what some call the winter/summer air cleaner. it is the one with the cable on the dash . I think it was more or less  standard equipment in colder climates, but that is only my opinion.  The green truck has a Donaldson air cleaner. I have usually seen these on trucks with turbos, or Cummins engines, although I would bet you could have ordered one on any B model. The Donaldson has a larger capacity . The bolt pattern on the cab is the same and either one will bolt up. The Donaldson has some different brackets inside the cab, and the air tube that goes though the cab to the firewall is different , too. The tube through the cab is some type of fiberglass or plastic. The air cleaner from the red truck is available. Steve

I have a winter/summer type air cleaner set up if you could use it. It does not have the separate bracket.

It is more likely that your timing is retarded than too far advanced.  When the spark occurs late, fuel can still be burning as it makes its way out the exhaust. Maybe you could set your timimg with a vacuum guage.  Or do it by ear. Just advance the timing as far as you can without getting spark knock under load. The timing marks don't seem to be helping any.  I doubt that the carburetor is the problem unless it is the wrong one for your engine. Pulling out the choke to make it run cooler is strange. Drilling your jets is not a normal repair for anything. The alcohol/water injection is a good idea, and will allow you to advance your timing more, but you really shouldn't need to add it. Another thought is that your cam timing could be off. Good luck

I installed a Garwood winch, the same model as Swishy's, on my B61. My transmission is a Quadruplex and I used a PTO with forward and reverse to drive the winch. An extra gear was needed to reach in to the pto drive gear in the transmission.  The pto drives two # 80 chains to the winch. It could have been a fairly easy job, but I got carried away and made the whole thing more complicated than it needed to be.  One of the things I didn't like was that the pto shifter, if mounted straight up through the floor, would have been right where a passenger's leg would be. I spent quite a few evenings making linkages to move that pto shifter over next to the 5-speed stick. I have not yet run the truck; it is still a work in progress.  Steve

Truck has been sold.  Thanks for looking.

DC Weasel, I have a 1966 B61 that was built with a 673C engine. It has a rotary injection pump and a pressed steel intake manifold. There are many differences in this late production B model compared to earlier B's I have noticed. 

The Quadruplex weighs 815 pounds.

Anthracite Auto Parts in Scranton PA has an L model with the 510 for sale. It is a straight truck with a long wheelbase and an oil tanker body. Pretty complete and worth saving.

Thank you MrsMackPaul. It's very nice of you to recognize our nation's birthday from the other side of the world !

 Steve

It would help to know what type of suspension your truck has, and what kind of road surface you were driving on. An unloaded Hendrickson walking beam on a concrete road will give the ride you describe. It's hard to imagine that tires with flat spots would perform any better at a higher speed. Good luck.