I have just finished replacing this plug and wanted to post the details that seem to be lacking in other posts on this topic.
First here are the details of what I have been doing to this engine so you can get a better picture of the situation. I have replaced the pistons, rings, bearings, timing set, oil pump and oil pump drive on the 428 in my F100.
Ok now for the interesting part. After I had finished all of the above work and double checking it all, I wasted no time in dumping oil in it, installing a new oil filter and priming the engine before starting. Well just as I have done many times before I was using my drill in reverse to turn the oil pump. Only a small amount of drag on the drill was felt. Well, as the drill kept on spinning I started to hear a strange noise like I hadn't heard before. It was oil squirting out of this little hole in the distributor shaft hole. Some of you already know that this is the lifter oil galley hole which is supposed to be plugged. Of course as my luck goes this plug is gone.
Now for the details that I could not find that deal with this.
The plug that worked just fine is a 7/16 which I measured with a micrometer at .446 and gives around .009 of interference.
For those who say that if you install this plug too deep it will block off an oil passage, well it isn't an oil passage, it is a lifter bore. If you do somehow manage to get a plug to drive that far into this oil passage you will know it when you try to install the engine's left front lifter. The reason is simple, the lifter will matter of factly just refuse to go into it's bore. For my engine and I am sure many others, it would be very difficult for this to happen because of the ridge in this oil passage near the lifter bore.
The type of sealer I was instructed by a machine shop to use is the hard setting gasket sealer by permatex.
After I finished installing the plug I waited several hours for the sealer to cure. Then I used the drill to spin the oil pump again and no leak. It sure did make me feel good to get that problem solved. I felt even better when I checked to oil pressure gauge and saw a much better reading than when the plug was missing. I can't wait to see the improvement in the running oil pressure. It has been on the low side for quite a while. The factory gauge has been showing a low pressure which I confirmed with two different manual gauges. They both had read 10-12 psi at idle with a cold engine. Don't ask about the hot engine oil pressure.
Anyway, I had never ran into this problem before and it seemed to be a little covered problem, so I just wanted to clarify a few points.
I did get my 428 running today and it ran ok except for a backfire through the carburetor and blowing the power valve. But, the great oil pressure that the engine has now compensated for that. I now have close to 28 psi even with a crappy idle rpm. The rpms are fluctuating a bit so oil pressure is hard to nail down right now.
The dash gauge for oil pressure has changed from just barely in the normal range to being near the O in oil. All of the hard work payed off and I couldn't be any more pleased with the results.
I was really not looking forward to installing this plug, but it turned out to be no big deal. I had almost the entire engine apart anyhow. It also gave me an excuse to replace the timing set.
I made a punch from round stock and coated the plug with sealer before driving it into place. Yes, I cleaned the oil galley hole untill it almost shined. It took an entire 10 seconds to install the plug. Now that I have had a machine shop installed plug blow out I will not allow the machine shop to do it again. It won't matter which machine shop either. After reading all of the bad experiences with the pressed in plugs I will probably go with all threaded plugs next time.
AH yes....the infamous dizzy plug. I found this little monster one time after a rebuild on race car motor(428). Here most times the shop would replace all the plugs, but maybe the screw in plugs in valley. He'd hand them to me and have me screw them in. Ok. Well this time HE forgot the dizzy plug and I did not KNOW he took it out. Same situation, though mine was ALL together IN the car!!! Couldn't get hardly any oil pressure at all. With some serious head scratching I made the call. He said "did you put that little plug in the front??". "What plug, you did them all, right?". So, off comes the timing cover, timing chain, in goes plug and put it all back together. Perfect!
Never have forgot to check for that stupid thing AGAIN!!!