Newly rebuilt engine (why rebuilt something let go ) so the old oil coolers used or new ones installed ? and or restricted oil coolers (water side or oil side ) or oil coolers too small and lack enough cooling for the motor oil ?

Nobody is going to ask clearances and what oil pumps? I would look at that, then go from there... I personally am a fan of loose clearances, HV pumps and 20/50...I see 80 PSI under way even hot... and the lowest I ever see is 30 hot at idle... mains are .003-.0035 and rear is .004

This thread is eye opening and also making me a bit nervous with my motor

I don't believe the 300 degree oil temp hurt the bearings That being said I have build circle track engines for many years and have seen many of those engines well over 300 degrees and no bearing problems.

I would say debris and tight clearances may a good place to start.

You said it was line bored I Not a fan of just line boring main lines should be finished with an align hone period.

most say boring but it's usually a hone,its just happens.

Ok, couple of things, if you have any of the oil left from the engine get it analized for fuel contamination, as Mike said does not take much fuel in the oil to kill bearings in a hurry...I found out the hard way. If that is good, and you did not want to go there but could have been bearing clearance and or the cranks/rods not being round, all of this needs to be checked, have had great engine builders miss stuff before.
the factory oil cooler/lines/fittings on a 502 are a joke on anything but a stock one, all of the pieces need to be trashed, block adapter, filter adapter, cooler, lines, if you look at the merc stuff you will see why. My guy feeling is that the it was/is rich enough to have fuel kill it..

with 90 hours on it i doubt it was a clearance issue or a pump issue.not knowing what the oil looked like when the failure happened we are all guessing a this point. i don,t have a clue as to who the builder is but with 90 hours on the engine i would say he did his job correctly and the failure might have been caused by a parts failure or some damage that started when the oil temp was in the 300 degree area.

what is it that makes you nervous with your build?

OK, to try to answer several of these posts: The mains clearances were set at .0025, r at .0027. This builder has been in business for over 30 years so I'm not going to argue with him about where to set the clearances. Theses are fuel injected so I've checked the a/f with a FAST wideband dozens of times- mid 12's at idle, mid 11's in the 2000 rpm range where it spends very little time, and consistently in the mid 12's at 3000+ rpms. As mentioned rods and crank were factory new (Scat) but the rebuild sheet lists "checking" rods and crank. Oil pump is listed as 601-1050 but I'm not sure of the brand. They did recheck the pickup placement and it was correct, 1/2" (I think) from the bottom of the pan.

Everything to from the remote oil filter is 1/2 inch and stock Merc parts. I removed all the lines after the season and having a guy here on OSO to make me up some new ones. Have never seen pressure above 50 psi and figured it was just my gauge. Also been noticing some lower pressure late in the season, so bought a mechanical gauge to check pressure in spring

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