Not a big surprise to me.  My TSIO-550 has slightly more hours on it, and last year the compression on the 3 left bank dropped to 50/80.

 

The hissing could be heard from the exhaust pipe, also.

 

Upon pondering and pondering, I decided to try something new, after all, I bought the engine in '96, and Continental would probably do their hat-dance if I complained, regardless of their terrible history with this problem.

 

So, I pulled all the plugs and sprayed about a half-pint of Kroil Oil in each cylinder.  Every day for two weeks I propped the engine to massage the cylinder walls and rings.  At the end of two weeks, I sucked out the Kroil Oil, changed the filter and the oil in the sump, put the plugs in and flew it.

 

Result-the cylinders jumped up to 68/80.  Stayed there, too.  So, what is happening in this engine?

 

In my case, I think the rings got coked up with combustion products and got permanently stuck in the choked compressive position.

 

In case you do not know what Kroil Oil is, you need to buy some of it and try it on various rusty, corroded tools.  If you put a drop of it on a bench top, it will creep out into a large circle for days.  It is marvelous stuff.  I use it all the time to release nuts from threaded parts.  Makes WD-40 look reallly bad by comparison.

 

The choice is ten bucks worth of Kroil Oil or a $9000 top end.  Worth trying?

 

David Jones