crank rub

u8at711 · 12-16-2012, 03:54 PM

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.

marc8090 · 12-17-2012, 09:19 AM

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.

12-16-2012, 03:54 PM	#1
u8at711 Registered Users Join Date: Sep 2010 Location: Enfield CT	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. __________________ YTD Nitro smoked = 14 Gal YTD Flights 0311 Gaui NX4 106 flights, Fury 55 026 flights Smokem' if you got em' To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

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12-17-2012, 09:19 AM	#2
marc8090 Registered Users Join Date: Sep 2006 Location: Long Island, N.Y.	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.