We bought a 1979 Freighliner tri axle dump truck. We have worked out most of the issues including one bad injector at Crosspoint Cummings. The last remaining issue is oil comming out the breather when the Jake Brake is applied. My first thought is rings? Other than that it is a good working truck. N14 Red Head engine, 15 speed with two low holes.
Jake brake runs off oil pressure, sounds like you have a blown seal in one of the jake assemblies and it's dumping oil into the top end faster than it can drain out. Watch the oil pressure gauge see if you get a drop when the jake comes on.
Run it with the valve cover off and have a look see. I've had a gasket upside down and it opened the oil passage to the rocker box before. Check the head you did the injector on.
You say 1979 with N14? What's the oil pressure at idle hot? Should be 20-22 psi and at 1800 rpm 40-44. If it's belching that much oil under the valve cover you should see a pressure drop with jake on like lantraxco mentioned. Do like Doyle said run it with covers off, could be a bad or leaking jake solenoid too. The top of the solenoid where it's crimped can get loose and gush. I have taken more than one oil bath . Truck Shop
Thanks all we have a starting point.
Never did find out if it got fixed.
I'm more curious if he has a n14 in a 79
There are lots of computer repowers out there, and just as many misprints.
NT, NHT N14, turn em upside down, they all look like sisters.
Two axe handles wide.
My n14 in a 1965 is one of them