Banana grooves..
So, first pic shows 2 sets of 273 rocker shafts. The shaft on the right has one oiling hole, and was used for a short time on a 340 hydraulic set up. The single round hole in the first pic would would be oriented so that it would line up with the oiling hole in the rocker during it's cycle. These holes are the same size and location on both shafts, and would provide ball/cup oiling and a little on the shaft in that area.
Pic 2 is where they differ......As you can see on the right shaft, there is definitely wear on the loaded side of the shaft. Since they were used for a very short time, I believe that they would inevitably score due to insufficient oiling. The shaft on the left has addressed this issue. A second hole with a banana groove cut right across the loaded part of the shaft spreading out the oil where it is needed.
I believe that both holes are needed to address ball/cup lubrication, and shaft lubrication when using adjustable 273 rockers with hydraulic pre-loaded lifters. From what I understand (info obtained here), with mechanical lifters, because of the designed lash, one hole is adequate because at certain points of the rocker cycle there is absolutely no pre-load on the rocker/shaft. This allows the oil to move around in the rocker arm/shaft fit clearance.........Just my thoughts!
BTW....Both shafts are OEM 273 shafts.
So, first pic shows 2 sets of 273 rocker shafts. The shaft on the right has one oiling hole, and was used for a short time on a 340 hydraulic set up. The single round hole in the first pic would would be oriented so that it would line up with the oiling hole in the rocker during it's cycle. These holes are the same size and location on both shafts, and would provide ball/cup oiling and a little on the shaft in that area.
Pic 2 is where they differ......As you can see on the right shaft, there is definitely wear on the loaded side of the shaft. Since they were used for a very short time, I believe that they would inevitably score due to insufficient oiling. The shaft on the left has addressed this issue. A second hole with a banana groove cut right across the loaded part of the shaft spreading out the oil where it is needed.
I believe that both holes are needed to address ball/cup lubrication, and shaft lubrication when using adjustable 273 rockers with hydraulic pre-loaded lifters. From what I understand (info obtained here), with mechanical lifters, because of the designed lash, one hole is adequate because at certain points of the rocker cycle there is absolutely no pre-load on the rocker/shaft. This allows the oil to move around in the rocker arm/shaft fit clearance.........Just my thoughts!
BTW....Both shafts are OEM 273 shafts.