After quite some time attempting to determine exactly what conditions led to
the situations that I experienced the syndrome I related it back to two
events...
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What causes the lifters to initially make noise is very simple.
The lifters have a hole in one side for oil to drain out and lube the lifter
bore.
The lifters are lying on their side and they will drain off the oil.
The situation isn't as pronounced in a V8 or I 4/I 6 because the lifters
still hold most of their oil.
New lifters will still make some noise but there are some rare circumstances
that they don't click on startups.
I find after the initial start up my lifters are quiet for subsequent
startups throughout the day.
If you have low oil pressure it might take a little longer for the lifters
to get quiet, hence the 29/50 or 15/50 oil is a help.
As for the Marvel Mystery oil, I think it cleans the sludge out of old
lifters and helps to build presure quicker without the sludge.
I've heard that steel and iron filings along with other new engine breakin
debris can get captured in lifters and impair their operation. (I've never
found any in lifters that I've taken apart.)

Stan Wilder
www.engineceramics.com