Hello guys
I joined a coupla years ago, and have been a happy camper up to now with my wonderful Jabiru JODEL. Reading JSB012-2 got my attention tho, and led me to disassemble the back end of the engine, where I discovered fretting between the "flywheel" and the VP coupling flange, and between the flange and the cshaft gear end. Now I am in the middle of the "flywheel" bolt saga on my solid lifter 2200 SN1757 with no dowel pins nor starfish, 200hrs on the Hobbs, 400+flights.
I am not inclined to remove the engine for the crankshaft dowel pin mod and associated starfish "flywheel" and thicker gear replacement thinking that the problem is mainly due to not enough clamp as you say.
Had not read your thread and intelligent analyses and approaches, but came up with a very similar approach as gregv's, except for the ARP bolts (can't find em in France- do you have a link to a web store please???), and machined hard steel 3mm X 16,5mm O.D. individual washers instead of the big washer. I also did the VP drive replacement spacer out of steel 5mm X 52mm O.D. but added qty 6, 5mm dowel holes between them on dia.44,5mm drill circle which will be reamed for ground pins driven into the reamed 5mm holes in the alloy "flywheel" and new steel spacer. The clamped sandwich will be between steel parts this way with a pinned drive of the alloy "flywheel".
Could you please give me your opinions, as well as the bolt link if possible, and some news of the mod you have implemented. I'm hoping to be back in the air next week.
Also, any comments on crank gear cracking and failure with subsequent wall thickening by Jabiru?..
Seems to me that root cause of all of this is perhaps prop related as Jab states in their litany of reasons. My prop fretted on the prop flange despite Belleville washers, and regular maintenance. (evidenced by brick red powder -iron oxide?-coming out between prop and flange, and fretting marks on flange. My prop maker says Jab prop bushings are too short, and end up crushing the holes in a circular direction, ovalizing them and permitting alternating circular movement evidenced by the fretting. This means the FLYWHEEL effect of the prop is incomplete, and there is a deficiency in rotational smoothing which then acts at the other end of the crank upon the friction drive of the " flywheel" AND produces circular shock loading of the gear which is driving camshaft and distributor shafts with their intrinsic inertias. Perhaps this causes pulsing rotation of the distributer rotor shafts, destroying the rotors, and requiring glueing- huh? suggested by Jabiru...
My prop guy suggested reinforced prop driver holes, longer prop bushings,and going from 1/4 24. Bolts to 5/16 or 8mm, and forget the Belleville washers...
Could this be the answer??
Your thoughts
Pierre
