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What's this noise?

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03 YZ125 with Athena 144cc big bore. Top end is new, no blow by or scoring visible on the piston. Tons of power, runs great and everything seems healthy except for this noise I noticed today. This is my second two stroke and I can't remember if my CR125 had a noise like this or not, but it doesn't sound right. It's a lot louder in the video than it seems to be in person, but just how the camera picks it up. 

 

Had the bike idling in neutral, pulled the clutch in and the noise was still there.

 

 

Edited by Torin

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11 hours ago, DocT said:

Sounds like a normal YZ to me bro.

Good to hear, just seems a little nosier than I'd expect but it's been a while since I sold my CR and don't remember how their engines sound. Thanks for the reply! 

 

Edit: Believe it is crank bearings. A bit of up/down play in the flywheel and makes a similar noise to what is being heard when moving it.

Edited by Torin

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Yep, bearing play will transition noise to what you can barely hear in the video. Check the big end bearing, it may be close to end of service life if a main has had play for a while. 

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7 hours ago, Gary YZDOC said:

Yep, bearing play will transition noise to what you can barely hear in the video. Check the big end bearing, it may be close to end of service life if a main has had play for a while. 

Already ordered a complete bottom end rebuild, so she'll all be replaced. Unfortunate as I haven't even had the bike out for a real run yet, but at least now it won't be a guessing game as to when it was last rebuilt. Thanks for the input guys.

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