Posted by: BobP on 22:51:08 12/05/14 Fri
Its pretty clear from Jabiru Australia comments on the CASA engine reliability concerns that they do not have a clue as to the reliability issues that the engine has, and more particularly as to which modification states/engine serial numbers have particular reliability issues. I have always believed that the Jabiru engine design is good but that certain ranges of engines have adverse reliability due to a few original weak points; the introduction of ill-thought design "improvements"; or because of the use of batches of defective/substandard components.
No doubt LAA will at some time take an interest in Jabiru reliability issues and, in the absence of definitive reliability information being available elsewhere I wondered whether we (all UK Jabiru owners) might be able to work with LAA to determine which groups of engines have particular reliability issues, and then go on to determine an appropriate inspection/upgrade regime for those engines to minimize the risk of in-flight failure / improve reliability. It seems to me that if the known (but never admitted to by Jabiru) problems were to be addressed, the underlying reliability (and credibility) of the engine would be re-established.
So my proposal is that a group of us with particular expertise/experience should get together and produce a detailed survey questionnaire. The questionnaire would then be reviewed and agreed with LAA and then circulated (via LAA if possible ) to all UK Jabiru engine owners.
By collating the results of the survey it should be possible to identify whether/what additional checks/modifications are appropriate to which engine groups, rather than draconian rework instructions being imposed from "above" in a knee jerk reaction. Innapropriate global edicts might be totally ineffective/inappropriate and even reduce rather than improve the reliability of some groups of engines.
For example my gut feel ( although a detailed survey could well prove me to be wrong) is that:
1) Aircraft fitted with wooden propellers and which have never had any prop-strike have a very low risk of flywheels falling off.
2) Loctite on flywheel bolts may be counter-productive
3) The batch of engines with grossly over-bored valve guides account for the majority of valve failures
4) Engines supplied before the batch with defective undersized through bolts carry minimal risk of through bolt failure, and so the risks associated with their replacement (breaking of the seal between crankcase halves and risk of subsequent oil pressure loss and/or fretting) would decrease rather than increase reliability.
5) Requiring the CHT sensor thermocouple to be in the head (rather than on a tag in the breeze) so true head temperature is measured and a meaningful maximum CHT can be defined (rather than some arbitrary measurement dependent on the exact location and trimming of the baffles (different for every engine ever installed)).
6) Requiring the oil pressure gauge to be located in the gallery to measure true oil pressure (with new limits defined).
7) Engines with the original economy jetting may be more prone to early failure.
Please post your thoughts on the above (for and against). If you would be interested in helping to develop a questionnaire please contact me at jabiru(curlyAsymbol]panth dotCOdotUk