Great low cost oil….but not s
as good for flat tappets anymore. They where the lsst holdout when the formulations had to change.

The OP has flat tappet lifters and oe stamped steel rockers.

I’m willing to bet these motors have an okling issue. Galley plug, cam bearing clocking? or ???

SB yea I'm not following all the oil stuff. Prob Wal mart oil would have suficed if oil flow was right.

Did someone mention oil galley plugs. I know that all the magnum engines that Mercury puts out there are 2 small tiny holes drilled in the oil galley plugs which is located on the front of the block on top of the cam shift behind the top timing gear. These plugs are to reinsure oil getting back to the oil Pan fast as the boat goes up-and-down over waves. This is what a Tech Support mercruiser service rep told me years ago. They don't want to wait for the oil to come down from the head they want to make sure it returns to the oil pan as fast as possible.

Drilling holes in the oil galley plugs has nothing to do with returning oil back to the pan quickly. That makes no sense. You are making a bleed point just to drain it back?

Those holes are too oil the timing chain.

In another thread the 4 plugs under the lifter valley pan were accidently left out on a gen 6 block causing low oil pressure, if thats what your are asking ?

Hopefully someone doesn't have the infamous restrictors in the galleys.

Roller rockers will fit under the stock Merc valve covers used on Gen V and IV engines. You just need to grind off the drip tabs which is what Merc does this on the blue engines. Not sure it will work on your Mark IV valve covers

And air purge that side of that galley to help keep hyd lifters from noise on start up.

the Mercury poly locks are about a 1/4 to 3/8 shorter than the ones that come with a new set of rockers

Did you ever see how much oil comes out of those 2 oil galley plugs when you start it up with no timing chain cover I can't believe it's just for the chain. Years ago at a mercruiser dealership they had a problem with a 454 and they started it up and that oil shot out of those plugs about 15 feet
and that was at idle for a few seconds. Either way that oil is getting back to that pan fast. Whatever you say it does, air bleeds for lifter galley, lubrication for timing gear chain, etc a mercruiser high performance tech person told me they want the oil back in the pan. period...his words