Merc 496 lifter oiling issue
 

What could be the cause of stock Merc 496 lifters (some/not all on left bank) all of a sudden clattering loudly after a WOT run? The engine/lifters has ~300 hours and is modified but the lifters are original stock. The engine now has a high volume oil pump that produces 50 psi oil pressure at idle with Mobil 1 15w50 silver cap after the the WOT run noted.

Usually if your lifters are clattering they're in need of oil. I don't mean oil pressure, I mean actual oil. How big is your oil pan? And, is your oil level good? I would check the dipstick if I were you. You might want to try filling to the top of the dipstick or a hair over and see if it helps the problem.

The pan is 10 quart, oil is on the full mark and like I said there is plenty of oil pressure which would have to drop if there were insufficient oil in the pan. Something else is going on. What is it?

Do you know what causes pressure? Resistance. Just because you have good pressure doesn't necessarily mean you have good oil flow/volume.

I understand/agree. I was only saying that there was plenty of oil in the pan or I would not have 50 psi pressure.

I am looking for insight/personal experience as to what has disrupted oil pressure/flow to the lifters in the past or other causes that produce lifter clatter after a run where lifter were quiet prior.

you stated the engine is modified,has this problem been happening since the mod,or is it something new,also,does it have oil restrictors,if it does get RID OF THEM.what mods does the engine have.

The Merc 496HO engine is now an HP3 Gen II except with all forged bottom end and stroked (521ci) for 70 hours/2 seasons. ~300 hours total on engine, 70 since the full rebuild. The stock oil bypass valves were replaced with 30 psi units and high volume oil pump then. This lifter clatter began after a WOT run just after the Crane rocker arm studs were replaced with ARP (a stud broke on the right bank) and replaced the old Comp 929 springs with new. Found a few of the old Crane studs slightly bent which is believed to have occured during prior shipping of heads and be the reaseon for the stud breakage. The lifter clatter is from the left bank. I also reversed the oil flow direction through the 3" Hardin thermostatically controlled oil cooler so as to flow counter to the sea water flow just prior to the WOT run noted.

Based on everything you've said up to this point, I'd pull that intake, rockers and push rods and have a good look at everything. All the speculation does not answer anything. Fun to talk about when you're bored and locked in doors but I wouldn't run it anymore until I had an answer. I don't believe there is anything you could do at this point to make it go away without getting the hands dirty...

Good luck!

i dont think the origional studs got bent during shipping.it sounds like you had some contact with piston&valve.was piston to valve clearance checked by the engine assembler?also,is the rocker arm geomatry correct.i think it,s time to take it apart&check everything.:party-smiley-004:

Oil starts at the back lifters and goes around each to the next lifter in line moving toward the front of the engine. For some reason (like a jammed lifter) oil is not making it all the way to the front of the engine. The lifters after the oil flow obstruction (or massive leak from a lifter that came apart) are pumping down and tapping. I would do as the others have said and pull the intake to check the lifters on the offending bank.

Bt