Originally Posted by ezobens
I am in the process of replacing the bearings in my Olds 455 powered jet boat.
It appears that the previous owner put the Mondello main bearing restrictors in mains 1-4. Has anyone used these before?
I'm questioning if the restrictors have been pressed far enough into the galleys.
I enlarged the upper bearing oil holes to 5/16" but the restictors still don't line up with the holes in the bearings and I am concerned if I will have enough oil flow to the bearings (see attached photos).
Since I'm replacing the bearings due to apparent oil starvation on the #4 main, I want to make sure I don't run into the same problem again.
Any suggestions or advice would be much appreciated.
One can see the restrictors are not placed properly and the worst is #3 where the restrictor has cut off flow from the pressure drilling to the bearing.
The Olds flows from the main galley via a drilling to each main bearing. It then taps drillings for the lifter galleys and the cam bearings using the back side of the bearing shell to close the passage.
Most main bearing inserts don't align the that bearing's feed hole to the crank journal depending instead of flow around the shell to the other distribution holes to suffice as a feed to the mains. I always considered this arrangement weak in terms of flow and similar to Cobalt, I align the feed hole in the bearing shell with the feed drilling, I prefer using the Dremel with a stone bit for the fine finish it leaves and minimum disruption to the actual bearing surface adjacent to the new hole. Left to my own devices I don't use restrictors as in my opinion they are a so-so fix aimed at the real problem which is the hole location in the bearing shell doesn't match the feed hole, depending on fluid transfer in that small slot to feed the bearing and the other two holes. The restrictor is an attempt to force more oil into the bearing at the cost of the upper end. These wild theories about drain back get sold to sell these parts, but as you can see with main #3 the feed to the bearing is greatly compromised by the position of the restrictor.
Boat engines always work hard compared to an automotive installation, the high volume oil pump is a good investment with the boat motors.