To touch on sb's comment of running the oil the bearing clearances dictate, the stock sealed 500's I've had apart were right @ .002 rods and .0020-.0022 mains. Pretty tight imop to run 20w50

Valid point. But (there is always a but right..lol) Merc suggests their 25W-40 right ? If cannot be found, 2nd choice straight 40w if over 50*F as next choice?

I agree with the above, but heck, one of the most popular oils to run for years with merc 500's, and similar, was Mobil 1 15w50. I don't think anyone had any oiling issues with it.

Fwiw, out of my Merc HP service manual

800sc Mains 1-4=.0025-.003 , #5 .0035-.004 ,Rods .0025-.003

600sc Mains 1-4=.0013-.0025, #5 .0024-.004, Rods .0025-.0035

HP500 Mains 1-4=.0013-.0025 #5 .0024-.004 Rods .0009-.0025

Thats production specs. Service specs, are a bit looser than that.

In this merc manual, it states that a 20w50 is recommended, or , a straight 40 weight if operating over 50 deg F. If operating between 32* and 50*, a straight 30 was recommened. . It covers the 525sc, HP500, 600sc, 800sc.

My own experience with morel link bar lifters is they are finicky to set. I can build 2 engines side by side, set both at 7/8 turn down (mid plunger travel), one quiet on start up the other slight cold chatter with 15-50 mobil 1. In every case I've been able to add 1/8 turn to the engine that has slight pre oil temp chatter and make it quiet.

Funny how everyone treats merc blue motors like the jewel of the Nile, I know my clearance tolerance is a lot closer than that. That manual reads like that of a gmc truck dealer.
Might as well say "as long as it spins, but doesn't wobble you're good"

Mercury racing might not be the jewel, but how often do their engines melt down with spun bearings, or oiling issues with 20 hours on them.

^^^ Mine & Joes are right there or a bit looser.
Rather have em looser than tighter.
Merc motors last, I would say they`ve probably done some research on that.

hp500 mains .0013 .0025.to me .0013 seems way to tight..0025 to .0035 is how i roll.i doubt ANY hp500 was ever built that tight.also .0009 rod clearance just plain scares me.

Runem loose! When I first starting with engine builds I was anal about going by the book on everything and then I woke up one day. All that is for ref and general information. Colder the oil temps the more the clearance.. This is a case where it's ok to NOT hit the side walls as long as your crank bottoms out. Little Friday humor. Ha

My last builds were .0035 and they ran forever.