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while working at a Mack dealer early '70's a major construction Co bought 20 brand new DM's . a few had blow by from valve cover vent. wasn't considered a problem. on the other hand, a used truck depending on mileage /hrs ; blow by doesn't always mean a needed engine rebuild. open oil filler cap  while it's running; how much blow-by out the cap vs out the vent.

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one thing I do is put my hand over the end of the tube and just feel the draft.. (I just did this for the ASET-C I just built)  I could feel the puffing of the engine, After I took it down,  #3+#4 pistons had stuck rings, both were the #2 compression rings.  My point here is that if it is not puffing hard it's good,  if its just warm and cuddley, and not puffing into my hand....  It's good..  sometimes just how the steam leaves the pipe can tell you..  If it just drifts away, its probably good.  if it blows to the ground,,  ya got an issue..  Come on Glenn,,  Tell me I'm right???   :)  jojo

Edited by Joey Mack
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 Joey you are a genius it generally means the engine is getting tired most times worn   compression rings  These days rebuild kits  are so expensive and you’re almost better off to find a used engine and I understand Mack  doesn’t sell them anymore for the END series bob

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But if you continue to drive it you risk spinning a bearing or a risk or wrist pin bushing but like Joey said if it’s not puffing that bad you probably don’t have anything to worry about I would be more concerned about exhaust smoke Bob

Edited by mowerman
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