Posted for "Frederick Moreno" <frederickmoreno@bigpond.com>:

 I have attached a summary report on pistons resulting from of a few days of
 research done by me and a friend with a lot of engine experience.  The
 expansion coefficients for aluminum silicon alloys was hard to find, but
 when I finally found it, it became real clear why forged pistons have larger
 expansion coefficients than cast ones.
 
 
 
 Credit the folks at ECI who diagnosed Steve Colwell's engine.  Steve then
 put me on the right track.
 
 
 
 Several have asked: do all the 10:1 Performance Engines have this problem?  
 
 
 
 I think not.  
 
 
 
 Stuart Featherstone acknowledged that two had suffered this problem out of a
 fleet of 60-70 IO-550 engines with 10:1 pistons (which are forged).  I think
 it was caused by a simple screw up of assembling the engine with the wrong
 cylinder clearance specifications - cast pistons use less clearance, and
 forged pistons need a lot more.  Make a mistake, and I do not see how you
 avoid the type of problem that both Steve and I found, and it happens very
 early, in the first 40-50 hours.  I suspect the pistons rub on the first
 engine rub on the test stand, but it takes a while for the ring grooves to
 subsequently pound out wider which leads to the ring flutter problem.
 
 
 
 Diagnosis method for ring flutter: Run some Polyflow tubing up the breather
 line to where it hits the tip of the dipstick, and then back through the
 firewall and into the cockpit.  Connect it to a spare airspeed indicator
 pitot port.  Put the static line from the air speed indicator through the
 firewall to the region below the engine baffling to measure "static"
 pressure.   This way you are measuring the pressure difference between
 breather line at the top of the engine and the ambient below the engine
 where the breather would normally vent.  
 
 
 
 Normal readings are around 30-50 knots.  I found these at idle, take off,
 climb, and cruise.  But reduce power below 18-19 inches for descent, and
 suddenly the pressure skyrockets.  Actually in our case, it went up for a
 moment, and then the air speed indicator which has been wiggling a lot (to
 be expected) suddenly held the needle still with no wiggles.  We were
 scratching our head when a few seconds later we could see oil coming up the
 line from the engine breather toward the airspeed indicator my buddy was
 holding in the right seat.  It gets your attention.  
 
 
 
 We determined that the fittings on the back of the air speed indicator were
 not fully tight, and leaked a tiny bit.  When the pressure soared as the
 rings started to flutter, oil pushed up the line killing the sensitivity of
 the instrument.  Upon landing, oil was all over the engine compartment
 splattered out the breather hose outlet since we had removed the air oil
 separator.  
 
 
 
 Ring flutter has special characteristics all of its own.  If you think you
 have the problem, try the experiment.   The crankcase pressure rises only
 during lower manifold pressure with cruise RPM.  It is very distinctive.
 And expensive to fix because the pistons are scrap like the Performance
 Engine warranty, it seems.
 
 
 
Fred Moreno