Checking Rod play? HELP

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11/10/2020 9:14 AM
Edited Date/Time: 11/10/2020 9:15 AM

Hey,

Link to vid: https://m.youtube.com/watch?feature=youtu.be&v=94vkfMrbqTo

Have a 2019 YZ250 that runs perfect. I’ve got a piston on the way just to freshen it up during winter, and wanted to check crank bearings just to make sure all is good.

The flywheel is tight in all directions. In out, up down, left right. Where I am confused, is rotating it back and forth. Going back and forth a very small amount, there is a noise coming from top end. My friend who’s an engine builder said it’s normal as you are going from one side of bearing to the other. Just looking for second opinion. (Sounds lime rotating it isn’t a test for anything)

Tried it on 2 other bikes and 1 bike did same thing that had fresh motor, and other kinda did just not as noticeable. Any thoughts?

https://m.youtube.com/watch?feature=youtu.be&v=94vkfMrbqTo

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11/10/2020 11:12 AM

I had a 18 KTM 250 sx at 51.5 hrs that had no up/down play in the rod. Also side/side play was fine. There was just a little bit of a snag when running the rod through rotation. Split the cases and mains where done.

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11/10/2020 11:30 AM

cdncombatmedic wrote:

I had a 18 KTM 250 sx at 51.5 hrs that had no up/down play in the rod. Also side/side play was fine. There was just a little bit of a snag when running the rod through rotation. Split the cases and mains where done.

main bearings are good, that’s why flywheel is tight in every direction. Trying to see if this knock is rod bearings. But i don’t think it is. Just unboxed 2021 and has same noise going back and forth

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11/10/2020 11:45 AM

Completely normal. The real test comes after you've removed the jug and piston. Only then can you accurately measure play/clearance on the big end of the rod.

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11/10/2020 11:46 AM

Yeah, it sounds like it's the little bit of slack or lash in the works. It's hard to assess the bottom end like this if the primary gear and clutch assembly are in. As you are doing that little back and forth you are turning all of that and the little bit of associated lash in those gears, etc.

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Powerband in every gear !

11/11/2020 4:25 PM

cdncombatmedic wrote:

I had a 18 KTM 250 sx at 51.5 hrs that had no up/down play in the rod. Also side/side play was fine. There was just a little bit of a snag when running the rod through rotation. Split the cases and mains where done.

hypermoto wrote:

main bearings are good, that’s why flywheel is tight in every direction. Trying to see if this knock is rod bearings. But i don’t think it is. Just unboxed 2021 and has same noise going back and forth

My flywheel was tight too...

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11/11/2020 6:20 PM

I think you are just feeling the backlash of the gear on the other side of the crank (clutch side).

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11/12/2020 5:46 AM

cdncombatmedic wrote:

I had a 18 KTM 250 sx at 51.5 hrs that had no up/down play in the rod. Also side/side play was fine. There was just a little bit of a snag when running the rod through rotation. Split the cases and mains where done.

hypermoto wrote:

main bearings are good, that’s why flywheel is tight in every direction. Trying to see if this knock is rod bearings. But i don’t think it is. Just unboxed 2021 and has same noise going back and forth

cdncombatmedic wrote:

My flywheel was tight too...

Tore it down. Everything measures out perfect and everything is smooth.

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11/12/2020 8:08 AM

There is spec in manual for the up/down rod play, should be some of that.

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11/12/2020 12:24 PM

rjg wrote:

I think you are just feeling the backlash of the gear on the other side of the crank (clutch side).

This was correct

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