CR125 now has a knocking noise after fly wheel damage

KICKERMAN360
Edited Date/Time 11/6/2013 12:33pm
So the engine in my CR125 only has 4 hours on it and one of the bolts inside the stator area came loose (the long one on the bottom) and bounced around inside, damaging the pick up on the fly wheel. Everything else looked in check, so I went and bought another used fly wheel off of eBay. Today I installed it and it still has this knocking sort of noise which has me wondering if any other damage has happened.

When it happened I was about to go WOT out of a corner and it just died, and puttered to a stop. I just attempted to kick it over but no dice. I roll back to our vehicles and remove the stator cover since I heard some noise from there and found the free balling bolt. I managed to start the bike again at the track but it had this knocking noise so I opted to just park up. When I installed the new fly wheel it still had the same sounds and doesn't seem to behave like it used to. I'm wondering if the bolt managed to somehow damage the bottom end bearings, although the inside of the cases are fine, except for scuff marks.

Any ideas on what to check?
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danman
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danman 11/5/2013 8:06pm
11/5/2013 8:06pm
Check to see if it bent the end of the crank that the flywheel attaches to. You can also grab that end of the crank and try to move it up and down. If it moves AT ALL, bad bearings, time to tear apart again.
That's all I can think of at this point.
KICKERMAN360 11/5/2013 10:06pm
11/5/2013 10:06pm
I took the whole stator assembly off to check for any play in the crank and there is none. I was slowly kicking over the engine those by hand and noticed even more odd noises, like something is grinding/scraping/hitting something. I'm uploading a video of it shortly. The thing that confuses me is that a) it ran perfectly with no odd noises before the bolt came loose and b) everything except the crank was replaced (the crank was within spec).

I looked into piston slap and it sounds somewhat similar to that when running. Although the causes of piston slap that would occur over time seem to be carbon build up but I have never fowled a plug on this bike, and it is jetted to Honda/FMF specs. I'll upload a video of it running when I get the stator assembly back on (probably tomorrow). I'm thinking of doing a compression test too.
KICKERMAN360 11/5/2013 10:43pm
11/5/2013 10:43pm


Near the end it's easiest to hear. I'm considering taking the top end off, but the gaskets are only 4-5 hours old which is annoying since they're practically new still.
project racer 11/6/2013 6:28am
11/6/2013 6:28am
If you do take the top end off, check the rod for any up and down movement. If the noise is still apparent with the stator compete removed from the engine, there is some other issue going on.

Cranks on 125's are a very high wear component.

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danman
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danman 11/6/2013 12:21pm
11/6/2013 12:21pm
If there isn't any play in the lower end, you have to tear into the top end.
I don't have time to listen to the video now, but will try to later.
FGR01
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FGR01 11/6/2013 12:33pm
11/6/2013 12:33pm
Get a dial gauge.

Mount the dial gauge to check for any out of roundness on the flywheel and also the end of the crank with the flywheel removed. You may have knocked the crank out of true when that bolt got jammed in there bouncing around.

If that all looks good, mount up the dial gauge with a spark plug adapter to touch the top of the piston. Move the flywheel slowly back and forth by hand and observe the dial gauge. If there is any lag or difference between movement of the flywheel and movement of the piston you have play in one of the rod bearings.

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