That is a grease cup and lubricates the distributor shaft. The "knob" is removed and filled with grease. Than with every chassis lubrication (every 1000 miles ) it is screwed down a turrn (see shop manua). If shaft is not lubrivated it can siese up in the distributor housing. Chassis grese may be used.
The adustment for the octane selector is made by slightly loosening the bolt just to the left of the distributor in your picture and advancing or retarding the timing. The line in the block casitng is the zero line and if you clean up that area you will see A + or - and graduation lines that indiacte how muchm the distributor has been rotated thus changing the timing. Should be advanced as far as possible with out causing the engine mto turn over hard due to too much advance.
I was going crazy trying to figure out what that part was!
I also noticed that advancing my timing made my car run much better. I had a local mechanic do my points and condenser and he set my timing to zero and it was hestitating and stumbling on acceleration.
They always ran better with the timing advanced as much as possible. In 1948 they would "ping" if advanced too for but with todays 87 octane gas it is next to impossible to make them ping.
Gene and I have shared posts about advancing timing on these engines. We agree they definitely run better with lots of advance. I also agree that it is almost impossible to get them to knock on 87 octane fuel.
Remember that the timing ball on the flywheel is at 5 degrees before top dead center (BTDC). If you set the octane selector at 0 and turn the distributor to fire when the pointer and the ball align, the engine is running 5 degrees advance at idle.
If you move the octane selector 5 notches (each notch on mine is 2 degrees) you are now running 15 degrees BTDC.
My '37 does not knock at that setting but it is harder to start. So I have moved the octane selector back to 4 notches which gives a total of 13 degrees BTDC. Runs great and starts pretty good when hot.
