Good Morning Continental Engine Owners,

During my annual this year (TSIO550E, 235 hrs, four years old), I found my Cyl #5 had a lower compression.  While all other cylinders were high 60's to low 70's (over the referenced 80 psi), Cyl #5 was 58 (warm).  After the oil was changed and the engine started and warmed up (but not with CHT reaching 300-350), retest of the compression was the same.

Reference the very important Service Bulletin document:

        http://www.tcmlink.com/pdf2/SB03-3.pdf

And then reference the Savvy Aviator explanation:

        http://www.avweb.com/news/savvyaviator/188758-1.html

Using the compression method described in the TCM service bulletin, with cylinder at BDC, pressurize 20 psi, bring to TDC, pressurize to 80 psi, then check leak down, the results were similar.  Important to this discussion is the reference Master Orifice reading, which was 44.

The next VER IMPORTANT step is to borescope the cylinder in question, looking for evidence of wall or valve damage or burns, moving though a full and complete cycle to inspect around the valve edges.  This was done and the cylinder was pristine.

Additional details: the engine has 235 hours of LOP operations, the plugs were excellent, the oil sequential analysis was unchaged, oil consumption was unremarkably normal (low), and EGTs were even across all cylinders.

I spoke to TCM Continental, who explained how this works.  If a cylinder shows low compression, you should run the engine (up to >300*F CHT) for 45-plus minutes and retest the compressions.  You must do the compression test as described in SB03-3 (abbreviated: BDC 20psi, TDC 80psi, etc) and also record the reference Master Orifice reading.  If the low compression is above the reference Master Orifice reading, borescope the cylinder and look for damage.  If there is no evidence of any damage, scorch, wall scores, etc, zip it up and go fly.  Check compression at the next 100 hr inspection.

I did get the impression that if the compressions were below the Master Orifice reading, the cylinder will probably show internal damage and will probably be pulled.

That's right...no damage on borescope equals no failure issues happening...do not remove the cylinder jug.

There are many reasons why a static cylinder can have low compressions but function perfectly fine while running strong and without any impending doom.

In fact, they recommend borescoping every cylinder at inspection, regardless of what the compressions do, since damge will be visible BEFORE compressions are effected.

Wow.   I told a friend that I will be watching cylinder #5 carefully, but it's problably the things I don't now that will kill me, not the things I know about.

This "borescope and don't remove the cylinder if visual inspection is fine" is different than the classic teaching, much like ROP vs LOP folklore.  TCM with their SB03-3  (March 2003) is trying to prevent the many expensive but unneeded cylinder repairs of the past.  Also notably, the reassembled cylinder is not guaranteed to be without fault after reassembly.

Of course, TCM says that I can recheck the compressions at any more frequent interval before the 100 hours (what ever I like), but it's not necessary (even if it will provide me some added piece of mind).  Like a physician, I will check in 10 hours, then maybe another 30 hours, and then another fifty hours.

I thought I'd share some of this hard earned tutorial with the ListServ members.

Jeff L

LIVP