I work for Bently, Nevada.
NOTE:
This is not a plug for Bently products!
Our market is large power generation stations/oil refineries, etc.
But the research done at Bently is paralled by none.
www.bently.com

I could go on for hours spewing information and quoting dissertations and
such, but I would recommend reading the ORBIT magazine from the bently
website.
There is always good information machinery diagnostics.

I would also recommend looking at some of the applications for Bently's
recip monitors (most of the monitoring is for rotating machines, i.e.
generators).
There has been a great deal of research in recip recently.
You can read some of the product literature, too.
In particular, read about the 3500/70M, the 3500/72M, and the 3500/77M.
These are recip impulse/velocity monitors, rod position monitors, and
cylinder pressure monitors.

It's probably way more information than your looking for, but it may come in
useful for an article.
It's not aviation specific, but more about machinery theory.
Bently also offers a machinery diagnostics class, which is pretty good.

Adam