HAI/ZAC NOBLE
be removed and found to be a good, unaffected part. After completion, the work could be signed off as per- formed and everyone would be happy. But that’s not what happened. The through-bolt was
removed, but even though the engine had been running well and hadn’t presented any signs of possible prob- lems, the part was indeed inaccurately engineered, as seen in the photo at right. (The bolt pictured on the right is the defective one.) The bolt’s center dowel section, which keeps the engine case from vibrating and chaffing during operation, was about half an inch out of position, potentially depriv- ing one of the case halves of the dowel’s support, thereby allowing it to vibrate. This, in turn, could have led to aluminum fretting and allowed the crankshaft bearings to slip, resulting in oil-lubrication and cooling problems. The end result could have been a loss of engine power.
Whose Guidance Are You Following? Back to our question of whether complying with a ser- vice bulletin is required. I hope you answered with a hearty YES. If you didn’t,
I hope you at least think it’s a good idea. Allow me to ask another ques-
tion: If you’re not following the manufacturer’s guidance, whose guidance are you following? Consider your answer carefully. Bottom line: Follow the manu-
facturer’s recommendations for maintenance. They have the expertise to issue the correct guidance. If that guidance comes in the form of a service bulletin, make sure it doesn’t pertain to your aircraft or appliance before you disregard it. Service bulletins are intended
to inform aircraft owners of prob- lems the manufacturer has identified with their product, or of enhanced ways to care for one’s machine. Ignore them at your peril. Fugere tutum!
The part on the right (above) was improperly engineered, with its center dowel section out of position.
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DECEMBER 2021 ROTOR 65
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