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Engines and Mufflers Having problems or need advice on Engines or Mufflers?


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Old 12-16-2012, 03:54 PM   #1
u8at711
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Join Date: Sep 2010
Location: Enfield CT
Default crank rub

heard a weird, grind noise scratchy noise, at the end of my last flight.

pulled the motor to replace the fan and install a back plate rpm sensor.

when the back plate was off, I noticed scratches from the wrist pin, the connecting rod has slop at BDC, is this normal ?

I checked for crankshaft movement, in out play, there was no play,

does my connecting rod need replaced ? is this a sign of the wrist pin going bad ?
the motor has never been over heated, and is newish, less than 40 flights.
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Old 12-17-2012, 09:19 AM   #2
marc8090
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Default

You will always get light scratches on the inside of the backplate. The top of the conrod is free to slide on the wristpin so the only thing keeping the bottom on the crankshaft is the backplate. It does rub. I would look around the inside of the case where the bottom of the conrod passes as the crank rotates for scratches. If you find any there, or on the side of the conrod's big end then that is not normal. That is a sign that the rear bearing is bad.
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