Oil pump shaft question

A thrust button is used on GM motors or any block that doesn't have a cam retaining plate. On GM motors there is nothing holding the cam from moving front except for the lifters on a tappet motor.
If you take the lifters and the dist. out you can take the cam out with the gear on it. When installing a roller cam a button is installed to keep the cam from moving front. The gear stops it from moving back.

On a chrysler the cam is held by a retaining plate. This is good except it prevents proper chain oiling from the front cam bearing over flow.. This plate which the timing gear rides against prevents the cam from being pulled rearward by lifter rotation. It is also used to hold roller cams in place on later motors. These plates and or tentioners have a oil grove cut in them unlike the early plates.. These should also be used when installing a roler cam. The clearance is designed into the step on the cam behind the plate. You should have at least .003 -.006 no less To much and you may need to shim.

The buttons on GM's are used in conjunction with a aluminum timing cover. If you don't see a aluminum cover in a SBC and they say its a roller motor. They don't know what they are doing and it won't last. The flex of the tin cover will cause roller failure . I have a billet mopar cover and want to use it for a cam button for better chain oiling.

Note the oiling goove in the later cam plate for roller cams