300+ rebuild

[fjh]

27 minutes ago, Joey Mack said:

I was taught the same thing.  Mack would only cut the journal that needed cutting. To this day i look at all the counter weights, and bearing numbers.. i dont assume. And Mack bearing kits are not always packed in the correct order.  I was blessed to have a cranky old Man take me under his wing... Earl Harnden was his name.   Maine Mack, 299 Warren ave. ,Portland M.E.   

I had to post his name.. He went home a couple years ago..  

RIP 🙏to him Joey ! Bless some of these guys we worked under !  Grumpy  or not  For their knowledge! Best we can  do is pass it on here! What goes around comes around! Grumpy is sometimes a good way to learn shit ! Sometimes there’s a reason! The biggest takeaway is PAY Attention ! None of this is written in books!

[Joey Mack]

Amen.. 

[BOBWhite]

On 7/12/2025 at 12:34 PM, Geoff Weeks said:

The tip turbine and Low Flow cooling were both attempts to better charge cooling without have to re design the front of the truck for enough room for an CAC cooling radiator (Air to air).

once trucks were being redesigned anyway, the reasons for the tip turbine and low flow systems went away. Having the charge cooler in front of the radiator give the best cooling, and what has become the std today. 

At the time, Mack tip turbine was revolutionary, both Cat and Cummins were still using water cooled aftercoolers, and low thermostat temps, to walk the fine line between good block temp and enough cooling for the charge air. 

 After Macks success, Cummins used the low flow system to run the "super cooled" multi-pass radiator coolant through the aftercooler, before sending it the engine. Cat never did and opted for the cooler in front of the radiator, which meant that their engines above 400 hp could not be fitted to many trucks. Cat engines below 400 hp still had the old water cooled aftercooler.

I didn't know that about the Cummins low flow engines. I know that they were mostly hated around here in tractors, they seemed to go through fan belts frequently and you'd have to keep the radiators sterile to keep them cool. The weird oil thermostats they put on Cummins later weren't much liked either

[steve s.]

13 hours ago, Freightrain said:

Not sure of year.  Only thing I have is serial on motor.

EtAZ673C 7S8762. If that means anything.

I

E- Mack diesel engine. T- trubocharged. A-single stage aftercooler. Z-maximum 10 grams per bhp/hr emissions level. Certified in California 1975-1976. 673- approximate engine displacement. C- variation of the basic engine unit, or(obsolete) emissions standard.

Your engine was rated at 295 HP and governed at 1800 rpm. If there was a B in the engine number it would indicate a Dynatard engine brake.

Edited 7 hours ago by steve s.
more info

[Freightrain]

Thanks Steve.  What I need to know is the serial number after the Etaz673c, does that correlate with anything?

7S8762 ??

[steve s.]

8 minutes ago, Freightrain said:

 What I need to know is the serial number after the Etaz673c, does that correlate with anything?

7S8762 ??

Sorry Larry, I don't have any information on your serial number. The Mack Museum could probably tell you more.

[mowerman]

That’s very interesting I thought 285 and 300 plus were 676????

[Freightrain]

I think the 285/300 were 676(maxidyne).  The 300+ isn't the same.

[mowerman]

it seems like its the same size as my block,,bob

[terry]

1 hour ago, mowerman said:

That’s very interesting I thought 285 and 300 plus were 676????

The 237 was a 675, and the 285 was 676, not sure on the 300+   terry

[fjh]

24 minutes ago, terry said:

The 237 was a 675, and the 285 was 676, not sure on the 300+   terry

Me thinks just different fueling! Comes down to gearing again Need gears for the 300 plus!285 not so much!

[Freightrain]

49 minutes ago, fjh said:

Me thinks just different fueling! Comes down to gearing again Need gears for the 300 plus!285 not so much!

Yup, from what I have read.

[Freightrain]

1 hour ago, mowerman said:

it seems like its the same size as my block,,bob

It is, just fuel and timing is different.

 

The "673" denotes a Thermodyne(multi gear trans) and the 675/676 was Maxidyne(5spd).

[mrsmackpaul]

1 hour ago, fjh said:

Me thinks just different fueling! Comes down to gearing again Need gears for the 300 plus!285 not so much!

Im fairly certain 285 Maxidyne is a air to air intercooled tip turbine job

A 300 Maxidyne is series air to air, so water cooling and tip turbine intercooled  job

A little more fuel and a more efficient intercooling and 300 Maxidyne was produced after 285 

In the Thermodyne it was the same and 320 went to 350 hp

We never had the range of motors, transmissions and backends etc that was available in the U.S.

So I have never heard of a 315 or a 295 hp motor 

Even gear boxes  5, 6, 10 and 12 speed 

None of the other numbers you blokes mention

 

Paul

 

[mrsmackpaul]

And even before the Maxitorque box was around, pretty much everything had a quad box and very occasional duplex

I have never seen or heard of triplex or simplex (think that was the name of Mack 5 speed) in Australia 

Paul

[mowerman]

duplex and triplex,,were very common here

[fjh]

19 minutes ago, mrsmackpaul said:

And even before the Maxitorque box was around, pretty much everything had a quad box and very occasional duplex

I have never seen or heard of triplex or simplex (think that was the name of Mack 5 speed) in Australia 

Paul

Odviously things are done differently down under! Paul! Couldn’t get 650 v8 here ever I would like to have seen one! With a vmac pump! Very interesting! We were able to at one point order the cam and turbo here through the Mack system we did two trucks up with the Aus turbo and cam with the pump jacked up they pulled like know body’s business!