Some one ask so I tried to explain in a PM. Rocker oiling

  1. Here is what I sent him so I copied and posted it here

  2. There is a hole in the block right above the head bolt The head has a hole in it drilled at and angle leading to the head bolt hole.

  3. The factory bolts are narrower below the head of the bolt and above the threads
    So the oil flows up along side the head bolt to the top of the head. Then it exits out of the head bolt hole in the head through another hole drilled at an angle that leads to the underside of the rocker shaft.

    The factory bolt is much narrower then the stud and many times it is not in the exact center. This may close of the hole entrance at the top or bottom.
    That is the reason for putting a passage in the stud. It insures sufficient oil to the rocker assembly.

    Now you will have guys that say they are getting oil. and it is possible if the stud is in the center or on the opposite side of the feed hole. But how much oil flow do they have at RPMs when you need it .

    Notice in the picture above the hole under the head stud ,

    Then in the the picture below the step in the bolts where they narrow above the theads and below the head of the bolt . This allows feed. The longer bolts are the feed bolts you only have one per side that feeds the rockers

    008555_v1_1.jpg

    On the studs pictured below there is no step down at all . So this restricts the flow. That is why we put a passage in the stud.

    Even with the passage in the stud they are still stronger then the Diameter of the base of the thread cut. We had no problem with the integrity.