Lancair Friends,

During my annual inspection, I found six cylinders with low compressions (20-30 over 80).  Yes, Master Orifice and all the right techniques.  We should know by now that BORESCOPE is the important step, and this was done.  Exhaust valve seats were eroded and pitted, causing leakage.  Valve face had mild thermal changes and stems were good.  A repair was planned.

Cylinders were pulled and inspected, confirming exhaust valve seats were the problem, and replacements were planned.  Further inspection showed some mild corrosion on some rods, wrist pins, even the cylinder barrels.  Evidence of moisture in the oil was apparent (more on this below).  I decided I would get the ECI Nickel+Carbide coating (CermiNil process).  The turn around time would have been four weeks minimum plus further reassembly and shipping, or I could get ready to go refurb'd compete cylinders, already coated and reassembled, immediately.  Hence, a complete Top End Overhaul.

Discussions regarding why this 2006 fast build TCM engine (flying since 2007, now out of warranty) was having this problem revealed several illuminating tidbits.  One custom engine shop said "those cylinders are doomed from the first time you run the engine."  Others explained that these engines are assembled with factory-style production, not custom production, and so parts are placed and efficiencies taken to improve production.  Another explained that the valve seats are pre-reamed rather than post-reamed after installation, creating an opportunity for poor interaction with the valve edge, malposition and wobble, leading to early failure.  This appears to be a common issue for the engines around my 2006 era.  It's not confirmed, but there is rumor that their practice of using pre-reamed guides ended after they finished using up their inventory in late 2007.

The moisture in the engine is presumed to come from the hanger's humidity, a result of poor pitch of the asphalt, seepage under the hanger door/edges, trapped moisture inside the hanger.  I fly once or twice a week, oil gets to 200*F typically before I open the oil door).  I have not opened and vented the oil filler cap after flight (and I will now).  I may add a dehumidifier in the hanger, and/or engine dessicator (ex, from Tempest) (comments welcomed).  I will see about moving hangers or more effectively sealing the perimeter of my hanger floor.  Other ideas are welcomed.

I have Chelton and full engine monitoring.  The engine's CAUTION warnings come on at a conservative 380*F CHT, REDLINE at 400*F, and only twice has CHT on two cylinders reached 412*F.  Oil consumption has been low.  Engine oil analysis every 50 hours has not been revealing.  I fly LOP and do the "Big Mixture Pull" shortly after take off, with 19 gph, 34"/2500 being a typical climb climb setting, occasionally keeping this in cruise vs 31.5".

Just sharing my recent experience with an expensive engine problem that's happened too early.

Jeff Liegner

Sparta, NJ