I Just cant Resist
Having fixed a few and flown a few here is my two bobs worth.
Jabiru engine failure modes,
1. Through bolts.
In the older solid lifter engines the tolerances would change often (for reasons I will expand on further in the next point) and unless you got the engines temperatures stable the user would have to constantly adjust the valve clearances so Jabiru decided to dumb the engine down by fitting hydraulic lifters. The mass of the solid lifter is tiny in comparison. Ergo large mass smashing back and forth pounding the thru bolts and they break.
2. Various Top End Failures.
The material chosen to manufacture the heads is ductile so that it can be CNC machined. The material has a higher plasticity when heated in comparison to the likes of a vacuum cast head such as Rotax uses. Jabiru finally recognized this when they started experimenting with vacuum cast top ends some three years ago but looked to me have made the same mistake as the coarse finned heads and didn't have enough surface area to transfer heat. Valves moving around in the guides and the seat as well as ladies waisting the valves from exhaust gases (stretching the valve in the exhaust flow, probably from insufficient diameter and surface area to transfer heat to an already hot guide) are all a result of heat retention and the ductility of the parent material.
3. Cooling problems Various
I have mates of mine who have persevered with Jabiru engines and now have many thousands of hours of reliable service from them. Anyone who knows will tell you to keep the CHT's below 110 C and the heads are a heap more stable. Then the solid lifter engine stops drifting in the valve clearance and presto no more tinkering there. Suddenly the through bolt tensions stop changing as well. These temps are easily achieved by opening the nostrils and putting extensions on the bottom of the cowls, careful checks for air leaks etc, no zoom climbs, all standard air cooling stuff.
4. Fuel Distribution
I am not going to expand on this because it is common to all aircraft engines and is the same old story, fit the engine analyzer now. In Jabiru's case they should just inject the engine, either electronically or manually.
In summary people should get of Jabiru's case. They have made some remarkable achievements on a shoestring budget using ingenuity and hard work. The air frames are a great product! Aircraft engine development is the holy grail and the big boys engines still f**k up all the time and at a much higher cost. However Rod Stiff needs to abandon the shoestring budget mentality (however altruistic) and start looking at more sophisticated production techniques and more custom parts rather than robbing cheap parts in mass production and working around them.
PS Don't bother arguing with Jaba on engines you will loose