When it comes to performing a compression check on a TCM engine one would do
well to carefully review their latest Service Bulletin (SB03-3) that covers
this subject. You can view it at

http://www.tcmlink.com/servicebulletins/index.cfm

A critical part of the compression check is to do the check on the
compression TESTER using the proper calibrated orifice tool. Without doing
this the lower number (i.e. the "60" in 60/80) is meaningless. Read the
bulletin for details.

One might assume (meaning making an ASS out of U and ME) that just because a
product is certificated that it in effect has the Good Housekeeping Seal of
Approval. Sadly not true. What it really means is that it meets the minimum
standard.

Take the GTSIO-520 engine found in the C-421. I've spoken with a variety of
operators flying these birds and don't know of any that made it to TBO
unscathed.

My recommendation would be to take a representative cylinder and have it
critically examined by a knowledgeable engine shop and ask them to make a
determination of the wear and/or failure points. Then check the replacement
cylinders for those same weaknesses and correct them as necessary. If the
valve to guide fit, seat grinding, etc. isn't up to snuff it won't matter
too much how nicely you treat your engine.

I will be attending an engine operating seminar in a few weeks.
http://www.advancedpilot.com/explore_001.htm
If I learn something revealing I'll pass it along.

One of the instructors will be John Deakin. He has written a few articles
(some of which are pre-class assigned reading) that you all may find
enlightening.
http://www.avweb.com/news/columns/182146-1.html

Jim ..... Please keep us all informed as your saga continues.

Ted Stanley - A&P-IA