Try the easy fix first

[ftcaruso]

I have a distinct disadvantage when compared to you all.  I did not do my Jabiru engine installation, and I was never all that mechanical in the first place.  Therefore when my #5 cylinder began indicating a 30 degree higher temperature than my next highest reading cylinder  (putting it into the “red” and very close to the maximum allowable limit),  I knew that I had some trouble shooting to do.  Having not flown the plane since mid February, as I had to get back to my spring time work projects, I could not understand why this sudden unaccounted for surge in temperature. However, during my condition inspection last month, I discovered that the original CHT ring sensors had a washer located between it and the spark plug port which I was  told was not a proper location.  I moved the washer back behind the ring probe and thought that maybe the original washer position might has acted as a “heat sink”, bleeding off some of the heat before it reached the probe.  This would mean that all of the cylinders would have always been running warmer, but not properly indicating same because of the washer position.  However, this overheating seemed to be isolated only to the #5 (right rear) cylinder.  

I followed Gary Weaver’s advice and moved the small metal “V” shaped head deflectors  from above to below the cylinders.  I nibbled away at the #5 cylinder air deflector epoxied to the top of the cooling shroud to allow for a greater air dispersal over that cylinder.  I changed the Bing carburetor main jet to the next larger size to allow more fuel flow, thus better cooling and a lower EGT. Steve Collins  thought that I should add a “lip” to the bottom of the firewall to better extract the air entering the cowl. Gary Weaver suggested that I cut away some of the lower cowl to allow a larger air egress area.  I even toyed with the idea of adding a $200 prop hub extender to the engine to allow better air flow through the cowl ports.  All good, although expensive, solutions.  

Today I had the epiphany that this problem had not manifested itself until I played with the positioning of the CHT ring probes.  On the chance that it may have become damaged, I changed the position of the #3 and #5 probes and went for a test flight.  Low and behold, the overheating was now showing up on Cylinder #3.  About the same 25-30 degree increase in indicated temperature.  It seems that all that I had was a bad probe sensor.  I ordered a replacement from Dynon and it should be here by Friday.  I will change it out, but how much easier would it have been had I tried this simple test first.  I told you that I am not very mechanical.

Frank

[Gary H]

Glad to hear you found the problem. What prop are you swinging and size? I'm having a little trouble not getting full RPM on take off. I put the aero carb on. Got to get it set right. The dang thing is really touchie and hard to set.

[ftcaruso]

Gary

I am using the Sensenich ground adjustable composite prop that came with the 3300.  I actually don’t know its length, but have it adjusted, right now, to provide about 2900 RPM at take-off.  I had reset it during my condition inspection last month to provide the 3300 max. RPM at full power, but that is when my overheating problem manifested itself.  I backed it down from my originally set 3000 RPM to that 2900, thinking that maybe the additional power might be accounting for the hot cylinder.  On Monday, when I head back to replace the defective CHT ring probe, I will re-adjust the max. RPM to about 3200, which is probably a good compromise.  This is a very easy adjustment with that prop.

Frank