What hole needs to be drilled Mr G? I've been running a mosh bosh of uppers/lowers with varying oil hole configs. All I have been doing is plugging the oil hole in either the upper or lower, which ever didn't have a mate. Is there an additional step I should be taking?

I was told the the front oil hole was an attempt by Mercruiser to solve some Drive Failures on higher HP setups and it didn't really help.....So plugging the upper on a newer drive and using the "pre 90" lower is ok .... As MG stated ...

We will see you next week right offthefront? Let me know the location where we meet up.

Dave

10-4 ...... I10 and 301 prob .... we'll set it up ....m

BT, if you look at an old upper case that doesnt have the oil transfer passage, you can see that there is a hole drilled in the front part of the cavity where the vertical shaft goes into the upper. I have drilled that hole, because that was the way it was done before the hole in the lower was designed.
The theory is that the lower gears act as an oil pump and push oil up to the pinion bearings and it flows over the pinion gear teeth. If you run a bravo with the back cap off, you can see it happening.
Without a hole in the lower, that cavity that supplies oil to the pinion bearings is closed off.. But I am not sure how the added hole affects this process. Just know they had it on the uppers for years before they changed it.
Dick

I think I get it Dick. If you run a newer upper having the tranfer hole, with a lower with no hole, you have to plug the upper transfer hole automatically. So to get the oil rotating (convecting) into the upper part of the upper you need to cross drill into the oil galley. I'll check that out, thanks for the info.

Dave

Yeah, that's it, the hole is on the front side of that cavity that the vertical shaft goes up into the upper ( not sure how to describe that tunnel ) and it is drilled on an angle, if I remember correctly.. a 3/8" hole, but I would have to verify that.. Been a while..