4.0 OHV break-in...

[35Remmy]

OK so the new 4.0 is ready to start in a couple days. The paperwork that came with the engine says to run at 1800 RPM for 30 minutes, then run from 30-50mph not too easy but not too hard from 30-50 MPH...stopping quickly. It says to do this at least 10 times in order to build compression and load the rings to the cylinder wall ensuring adequate break-in. The machine shop from the last motor I had rebuilt said to do the same thing from 30 to 50MPH but to just let off the gas to build compression and load the rings. Is one method more correct than the other? It also says to just use the manufacturers recommended oil for break-in...I'm just using plain 'ol Valvoline 5W30 and and the good 'ol FL-1A filter.

 

[Snoranger]

The paperwork that came with the engine says to run at 1800 RPM for 30 minutes,<-- This is to break in a flat tappet cam, your roller cam does not need it.

then run from 30-50mph not too easy but not too hard from 30-50 MPH...stopping quickly. It says to do this at least 10 times in order to build compression and load the rings to the cylinder wall ensuring adequate break-in. The machine shop from the last motor I had rebuilt said to do the same thing from 30 to 50MPH but to just let off the gas to build compression and load the rings. Is one method more correct than the other? It also says to just use the manufacturers recommended oil for break-in...I'm just using plain 'ol Valvoline 5W30 and and the good 'ol FL-1A filter.

I usually just warm roller cam engines up to operating temp, watch for leaks, adjust timing/carb (if necessary),etc. Then drive it. Dont baby or beat on it, just drive it normal. Vary the RPMS (2-4k), dont get on the highway and cruise at a constant speed. Change the oil at about 500 miles.