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0 ticedoff8
rrKey Veteran Morgan Hill, CA. USA |
How did my YS 91SR-3DS break the crankshaft? WTF!?! YS 91SR-3DS with maybe 70 to 100 flights.
First flight of the day and the crankshaft breaks. I flew it 5 flights 3 days before and nothing had changed.  Why did this crankshaft break?Everything was going normally.
I am about 3 min into a normal 5 min flight. Good smoke trail, good power, no hard 3D. Then, it misses a few beats, and then picks up. Misses a few more beats and starts to sound labored. I've heard that sound before so I hit throttle hold and do a wonderful autorotation back to my take off spot. The engine died when I hit throttle hold and was not idling when I landed. I go back to my box, and the motor seems a little hot - but the starter shaft turns and it doesn't seem too bad. I spin the motor with the starter - seems normal. I hook up the glow and it starts okay - idles okay. Humm. I shut down and check a few things - seems okay. I start it back up, walk out to the box, spin up and lift into a hover. Everything seems okay - I land, check the backplate - normal temp. Spin it up, climb into a hover, hold the hover for about 20 seconds and it starts sound labored (loading up) and missing. Then, it stops.When I try to turn it by hand, it is stiff and tight. I try to spin it with the starter - and it is really tight.When I took it apart on the bench, the counterweight & main bearing came out as a unit.The last real "crash" was about 3 months ago when a linkage broke on the cyclic. But I had throttle hold engaged when it hit the ground. |
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| cabeng
rrApprentice South africa |
trying to turn the motor over with the piston locked over time will cause this , also possibly if there is a "Stress raiser" point along the crank at to point that it broke , check the crack line very carefully , is there a point that the diameter changes , even very slightly , or even a machining mark on the inside that made a "deepish scratch" ? that coupled with a few hydraulic lock conditions and possibly even a slightly over hardened shaft all come together to give you what you have , A 2 piece crank!If there is any evidence of machining marks along the crack line , I would send it off to YS for a "manufacturing defect" claim |
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| ticedoff8
rrKey Veteran Morgan Hill, CA. USA |
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| Ace Dude
rrProfessor USA |
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| ticedoff8
rrKey Veteran Morgan Hill, CA. USA |
Other than that, I guess I could call YS support in Reno and see what he thinks went wrong.It is clear now that the labored engine sound and the high heat (after the first engine cut-out) was related to the broken back-half of the crankshaft and the main bearing moving back and rubbing the steel backplate.It is just so weird that the engine would keep running pretty well even with a fractured crankshaft. I have no idea how long it was cracked / fractured. I figured it would just quit.Every other internal part looks fine. All I would need to do is buy a new crank and have the engine running in 20 min. |
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| carcrasher
rrElite Veteran east coast |
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 TMoore
rrMaster Cookeville, TN |
The only ZERO flight hour certificate in the world. It's like getting a driver's license without the driver's test. |
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 Tyler
rrElite Veteran Chicagoland area |
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