- Fri Jul 27, 2018 2:10 am
#404116
Let's share some stories about metal fatigue and the importance of routine maintenance checks.
It's mid-winter down here in Auckland, New Zealand, and there are squalls everyday it seems. I decided to fire up my Mosquito NRG in the garage, just to flush some fuel through the carburetor and keep her turning over.
I have had troubles with the exhaust system and metal fatigue in the past. The new exhaust system is a lot better than the old one. I now safety-wire the two cap screws that hold on the exhaust manifold. I used a 1.5 mm cobalt drill to deal to the high-tensile steel of the bolts. Imagine my surprise when I discovered that one of the bolts had broken in half. The bottom half of the bolt and the offset hex nut were long gone. Only the locking wire was holding the head of the bolt in place.
I decided to replace the other bolt. I found a crack in the offset hex nut. Luckily I had spares from Sweden.
After replacing the manifold blots, I checked the rest of the exhaust and found that the exhaust manifold supporting strap had fractured where it was welded to the exhaust pipe. It was a lousy weld to start with (only one side of the strap was welded to the exhaust pipe).
The gunk all over the exhaust springs is silicone sealer. It's job is to dampen any spring harmonic vibration and so prolong the life of the springs (which are also safety-wired).
Today I picked up my re-welded exhaust. I'll re-assemble everything tomorrow and fire up the engine. Maybe I have a vibration problem? I haven't dropped, knocked or otherwise abused my harness, and I take great care not to strap it down on my car roof-rack anywhere near the engine or exhaust.
The take-home message is to regularly check all parts of your power harness for cracked welds and lose bolts. Safety wire is your friend.
I invite you to share any of your stories about broken things you discovered in your checks of your equipment. I hope we can all fly safer.
It's mid-winter down here in Auckland, New Zealand, and there are squalls everyday it seems. I decided to fire up my Mosquito NRG in the garage, just to flush some fuel through the carburetor and keep her turning over.
I have had troubles with the exhaust system and metal fatigue in the past. The new exhaust system is a lot better than the old one. I now safety-wire the two cap screws that hold on the exhaust manifold. I used a 1.5 mm cobalt drill to deal to the high-tensile steel of the bolts. Imagine my surprise when I discovered that one of the bolts had broken in half. The bottom half of the bolt and the offset hex nut were long gone. Only the locking wire was holding the head of the bolt in place.
I decided to replace the other bolt. I found a crack in the offset hex nut. Luckily I had spares from Sweden.
After replacing the manifold blots, I checked the rest of the exhaust and found that the exhaust manifold supporting strap had fractured where it was welded to the exhaust pipe. It was a lousy weld to start with (only one side of the strap was welded to the exhaust pipe).
The gunk all over the exhaust springs is silicone sealer. It's job is to dampen any spring harmonic vibration and so prolong the life of the springs (which are also safety-wired).
Today I picked up my re-welded exhaust. I'll re-assemble everything tomorrow and fire up the engine. Maybe I have a vibration problem? I haven't dropped, knocked or otherwise abused my harness, and I take great care not to strap it down on my car roof-rack anywhere near the engine or exhaust.
The take-home message is to regularly check all parts of your power harness for cracked welds and lose bolts. Safety wire is your friend.
I invite you to share any of your stories about broken things you discovered in your checks of your equipment. I hope we can all fly safer.
Attachments
Manifold strap close_up.jpg (1.8 MiB) Viewed 2462 times