The plug on the side of the head was how the factory drilled across for oil access to the rockers. On a 55-58 235, the rockers are fed oil via the rear cam bearing. So if you pulled the side cover, you would find a steel line that ran from the back cam bearing boss up to a fitting just below the boss that you are referring. Oil was metered through the head to the copper rocker connector. That oil is supposed to dribble out from the rockers, not spit. Oil dribbles from the dribble hole on each rocker to lubricate the rocker arm adjuster ball and push rod cup, and the spring and rocker arm tip. If it is spitting, it misses those vital parts and hits the inside of the valve cover. It’s not all that uncommon to see a reduction in oil flow to these motors through a combination of a worn cam bearing allowing pressure to bleed off, and a clogged line. The aftermarket came to the rescue by selling little kits that took oil from the oil sender port on the driver side or the output of the oil filter (which dumped the clean oil directly into the pan where it was instantly diluted with dirty oil anyway) and ran it into that drilled passage which is a direct feed to the rockers. The 55-58 rockers have a groove inside the rocker that directly intersects the dribble hole. If you had to replace the 55-58 head with a later 59-62 head, you had to use the drilled bolt and plug arrangement to cut the oil flow to the rockers so that it would not spit but dribble.
For the 59 and up, gm changed the oiling system to create a sort of pressurized system to the rockers . Those blocks do not have a steel line from the rear cam bearing but use a drilled passage directly up from the main feed. The metered oraface for the later head is larger than the earlier head. For these motors, it’s the same issue, the drilled passage gets clogged so you used one of those little copper kits. The rockers are different for 59-62 in that the groove inside each rocker is offset from the dribble hole, and the rocker connector copper tube is pinched off.
Those aftermarket copper line kits were small lines. The reason for the small lines is that with these bypass motors, if you used too big a line you bled too much pressure from the mains starving the main and rod bearings. If you have a an issue with the rockers getting oil, and you want to install one of these kits, and your motor has a bypass oil filter, consider running the line from the output of the filter to the fitting on the passenger side of the head. Running it this way keeps the number of sources tapping oil pressure from the motor to one (as opposed to two, the oil filter and the aftermarket line) which helps keep the pressure up and has the benefit of providing the rockers with clean filtered oil.
Last edited by Dragsix; 01/03/2018 3:22 AM.
