Blow by on fresh rebuild?

Blowby happens under a load, it doesn't happen sitting and idling,

 

No, this is backwards. Blowby is compression gasses that get past the piston rings and into the crank case. This happens at idle because there is not enough cylinder pressure to force the top piston ring out tightly against the cylinder wall.

 

was it just an in-frame or was it a full-blown overhaul? Pistons, rods, connecting rods, crankshaft vibration dampener liners, crank shaft bearings?
if just an inframe and they didn't do anything as far as new in the guts of the motor on the bottom pulling it out overhauling it completely then anything's possible it's very game

 

My truck has some blowby at idle. Detroit 60

 

My Detroit pushed oil through the rings, didn’t notice much blow- by, basically the same thing though, if not worse than his blow-by. Once the rings wear into the sleeves, and get matched up good and seal up it should go away.

 

Omg. So much scewerd info in this thread.

Diesel engines have blowby at idle because there is no tension on the rings as stated. Keystone rings dont seal very good till there is cylinder presuure. This is why you need to work them hard when just inframed or rebuilt.
Now then some engines are worse then others at idle. Series 60s always have had more blowby at idle then most but perfectly normal.
To say they dont have blowby while under power is false also. Depending how worn out your engine is you will have blowby under power . Cat accerts have a ton of blowby when pulling because of the high boost they produce. They even have catch cans to catch the oil out the tube factory. So you can have blowby at idle and pulling depending on the condition and make of your engine..

To answer the OP question. Sounds like you have to put some more hard miles on your engine as others have stated already.

 

You’ll have to hear some expert opinions on the subject. But I can remember heavy haulers used th run a winter front after Overhauls. In order to let it run hot and seal up rings quicker. Running it hard puts more fuel, thus more heat. Makes sense to Me anyway