AMGeneral
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Well folks, as trouble free as the 673 Mack engine usually is,every now and then you run into one that has troubles,being that Mr Murphy haunts me ALMOST as much as he does Wreckerman,I have 2 with the same problem.
A little engineering info on the Mack that you'll find under the hoods of some M39 series 5 ton trucks......
673 ci displacment inline 6 cylinder turbocharged diesel
211 hp @ 1900 rpm
611 ft/lbs tq @1500 rpm
2 valves per cylinder vs 4 as in the later Mack engines
it uses a American Bosch APE series inline injection pump and Bosch injectors similar to the Multifuel design.
But it differs from the Cat and Cummins engine designs for the cam followers/tappets,the Mack uses a flat tappet design vs a roller as the Cat and Cummins engines.
Herein lies the problem,whether it is caused by the removal of certain friction additives from engine oil over past years or the fact that the tappets themselves only have a face hardening of .005 thickness,irreguardless it tends to wear out cam lobes at a rapid rate.
I actually have diagnosed 2 of my engines to have this same problem,1 just has a small but noticeable miss,the other has a lesser miss,but a much more pronounced hard rap noticable just above the cam at the tappet level on the right side of the engine. Since I already had engine #1 out for fitting in another truck it seemed the best candidate for teardown and repair.
Upon teardown of the engine and measuring of the cam lobe lift,all were within specs except for #3 intake valve,it measured .021 less lift than the other 11,I also noticed that the valve spring for that particular cam lobe was installed upside down,kind of an odd coincidence. This engine shows a rebuild at TEAD in 1975, with bore at STD and rods/mains at .010 oversize bearings,probably the last time it was apart.
I will post pictures and updates as the repairs/ progress,as of now I am ordering a updated cam and tappet set with hardened faces of .013 thickness.
A little engineering info on the Mack that you'll find under the hoods of some M39 series 5 ton trucks......
673 ci displacment inline 6 cylinder turbocharged diesel
211 hp @ 1900 rpm
611 ft/lbs tq @1500 rpm
2 valves per cylinder vs 4 as in the later Mack engines
it uses a American Bosch APE series inline injection pump and Bosch injectors similar to the Multifuel design.
But it differs from the Cat and Cummins engine designs for the cam followers/tappets,the Mack uses a flat tappet design vs a roller as the Cat and Cummins engines.
Herein lies the problem,whether it is caused by the removal of certain friction additives from engine oil over past years or the fact that the tappets themselves only have a face hardening of .005 thickness,irreguardless it tends to wear out cam lobes at a rapid rate.
I actually have diagnosed 2 of my engines to have this same problem,1 just has a small but noticeable miss,the other has a lesser miss,but a much more pronounced hard rap noticable just above the cam at the tappet level on the right side of the engine. Since I already had engine #1 out for fitting in another truck it seemed the best candidate for teardown and repair.
Upon teardown of the engine and measuring of the cam lobe lift,all were within specs except for #3 intake valve,it measured .021 less lift than the other 11,I also noticed that the valve spring for that particular cam lobe was installed upside down,kind of an odd coincidence. This engine shows a rebuild at TEAD in 1975, with bore at STD and rods/mains at .010 oversize bearings,probably the last time it was apart.
I will post pictures and updates as the repairs/ progress,as of now I am ordering a updated cam and tappet set with hardened faces of .013 thickness.
