Transmission/Lower End Noise '21 YZ250 w/ 30 Hours

vansnxtweek489
I have done some research but not really finding a solid answer. Some say low oil, others say undertorqued parts in the right side of the crankcase.

Basically it sounds like my bike has a turbo diesel in it. It runs great with no lack of performance but consistent with the RPMs I have a whirring noise. I change my transmission oil every 7 hours or so and this started about 2-3 hours after the last change. Put 750cc in just like I always do.

Before I start taking stuff apart on this nearly new bike was hoping someone here had some prior experience with this noise and could guide me where to look.

Thanks (and I know noise threads suck)
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Rickyisms 3/10/2022 7:50am
3/10/2022 7:50am
Any chance you can post a video?
1
mxracer666
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mxracer666 3/10/2022 8:14am
3/10/2022 8:14am
In my opinion, 7 hours in a 250F is a looong time to go between engine/transmission oil changes. 750cc is a tiny amount of oil - consider what it's doing in there. You'll need to pull off the clutch and inner right-side case cover and check every bearing. Likely the sound is coming from a bad bearing. Have you been able to compare to other 250F's of your model? Good luck!
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Grouper
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Grouper 3/10/2022 8:21am
3/10/2022 8:21am Edited Date/Time 3/10/2022 8:24am
Exactly like a straight piped turbo car at low rpm right? Distinct whistle? Carries with RPM but gets drowned out by engine noise? Does it seem to come from the right side?

Upload a video to youtube shorts if you have a google account, its very quick and easy. I did it for another thread.
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Falcon
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Falcon 3/10/2022 8:45am
3/10/2022 8:45am
mxracer666 wrote:
In my opinion, 7 hours in a 250F is a looong time to go between engine/transmission oil changes. 750cc is a tiny amount of oil -...
In my opinion, 7 hours in a 250F is a looong time to go between engine/transmission oil changes. 750cc is a tiny amount of oil - consider what it's doing in there. You'll need to pull off the clutch and inner right-side case cover and check every bearing. Likely the sound is coming from a bad bearing. Have you been able to compare to other 250F's of your model? Good luck!
He said YZ250 - 750cc is the manufacturer's recommendation for that model. The recommended oil change interval is 12.5 hours, although I agree that more often is better. (In a 250F, I'd do it every couple hours, for sure! Those are sharing transmission oil with engine parts and the oil gets fouled with combustion byproducts.)
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mxracer666
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mxracer666 3/10/2022 9:03am
3/10/2022 9:03am
Aaaah! My bad! I blame my lack of coffee at that hour. The required inspection still applies tho...
vansnxtweek489 3/10/2022 9:42am
3/10/2022 9:42am Edited Date/Time 3/10/2022 9:43am
Grouper wrote:
Exactly like a straight piped turbo car at low rpm right? Distinct whistle? Carries with RPM but gets drowned out by engine noise? Does it seem...
Exactly like a straight piped turbo car at low rpm right? Distinct whistle? Carries with RPM but gets drowned out by engine noise? Does it seem to come from the right side?

Upload a video to youtube shorts if you have a google account, its very quick and easy. I did it for another thread.
Yes, 100%. This is what I would compare it to. At first I thought it was maybe an air leak at the exp. chamber/silencer joint or even at the cylinder but its def. an internal noise.

I will grab a video when I get home from work, I agree, I think it should be pretty easy to hear that way. Thanks ya'll for the help!
Moto520
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Moto520 3/10/2022 12:58pm
3/10/2022 12:58pm Edited Date/Time 3/10/2022 1:23pm
pull the clutch cover off and check all that....It could be a loose bolt rubbing against the cover or something simple like that. I would definitely start with the clutch
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kijen
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kijen 3/10/2022 5:40pm
3/10/2022 5:40pm
Sorry for my stupid reponse, but if it increases with, rpm without being in gear, check stuff that spins up, clutch water pump, governor?
Try a harbor freight stethoscope?
FGR01
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FGR01 3/11/2022 9:28am
3/11/2022 9:28am
Yeah, this sounds like either a clutch spring bolt has backed out or the infamous YZ250 primary gear bolt backed out (this thread).

In any case, I'd be taking that right side cover off to see what's going on.
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sandman768
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sandman768 3/11/2022 6:41pm
3/11/2022 6:41pm
Drain oil, look for metal shavings or particles that would indicate something is wrong, bolt backing out ect. Pull clutch cover & inspect, if nothing, pull water pump cover to inspect impeller. I always ran 800ml”s in my YZ”s…is pipe mounts broke? If nothing wrong with water pump impeller, I would then pull powervalve cover off & inspect….
vansnxtweek489 3/12/2022 4:46am
3/12/2022 4:46am
Thank y’all all for the responses. Definitely going to clean the bike up and take the right side cover off and see what’s going on. It’s definitely something rotational running in there. I hope it’s just something dumb. How does this happen from the factory ? 😒
vansnxtweek489 3/16/2022 3:57pm
3/16/2022 3:57pm
I'm sorry to bother ya'll, but wondering if anyone listened to that video I took. I drained the oil and removed the right side engine cover. I didn't seem to see anything out of line and checked bolts and such. The noise just seems odd to me but the bike runs well and nothing seems out of order. Just don't want the thing to lock up on me off a jump or something. Only thing I can find in other threads is water pump shaft/seal noises but I've never heard a bike make this dieselly/turbo type noise.

Thanks
Factor E
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Factor E 3/16/2022 5:48pm
3/16/2022 5:48pm
Crank bearing
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Moto520
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Moto520 3/16/2022 7:06pm
3/16/2022 7:06pm
It’s something…..could run forever like that or it could get worse quickly. I would track it down
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Rickyisms 3/17/2022 1:16pm
3/17/2022 1:16pm
My KTM 125 had an identical (louder in person sound) a couple weeks ago that turned out to be the crank bearing.

Take off the inner clutch cover and stator covers and check for vertical play in the bearings, turn over the motor slowly by hand put your ear near the crank bearings, I was able to deduce mine down because I could hear a slight squeal while turning the engine over by hand.
vansnxtweek489 3/18/2022 4:42am
3/18/2022 4:42am
Rickyisms wrote:
My KTM 125 had an identical (louder in person sound) a couple weeks ago that turned out to be the crank bearing. Take off the inner...
My KTM 125 had an identical (louder in person sound) a couple weeks ago that turned out to be the crank bearing.

Take off the inner clutch cover and stator covers and check for vertical play in the bearings, turn over the motor slowly by hand put your ear near the crank bearings, I was able to deduce mine down because I could hear a slight squeal while turning the engine over by hand.
Thanks man. I will check for play in those bearings. I swear if I've got a smoked crank bearing on a new bike....I don't even know what to say. Literally the reason I got a new bike vs. screwing with the older ones I had.
Rickyisms 3/18/2022 7:13am
3/18/2022 7:13am
Rickyisms wrote:
My KTM 125 had an identical (louder in person sound) a couple weeks ago that turned out to be the crank bearing. Take off the inner...
My KTM 125 had an identical (louder in person sound) a couple weeks ago that turned out to be the crank bearing.

Take off the inner clutch cover and stator covers and check for vertical play in the bearings, turn over the motor slowly by hand put your ear near the crank bearings, I was able to deduce mine down because I could hear a slight squeal while turning the engine over by hand.
vansnxtweek489 wrote:
Thanks man. I will check for play in those bearings. I swear if I've got a smoked crank bearing on a new bike....I don't even know...
Thanks man. I will check for play in those bearings. I swear if I've got a smoked crank bearing on a new bike....I don't even know what to say. Literally the reason I got a new bike vs. screwing with the older ones I had.
The crank bearing experience I posted about was just a couple weeks ago. Just over 18 hours on brand new OEM everything. Shit happens🤷🏻‍♂️

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MotoCoUSA
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MotoCoUSA 3/28/2022 10:51am
3/28/2022 10:51am
Any update/solution on this. I was riding mine (21 250x) around my property turn track after changing trans oil and noticed something similar, not nearly as loud as yours, but definitely a noise that was different. Thought maybe my air filter didnt get a good seal or something I dont know. Thanks for any info.
mwssquad827
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mwssquad827 3/28/2022 2:30pm
3/28/2022 2:30pm
Ya what’s up with this noise?? My 21 yz 250 makes the same noise as the video…
Rider 5280
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Rider 5280 3/28/2022 10:53pm
3/28/2022 10:53pm Edited Date/Time 3/29/2022 9:07am
Is there any way this could be powervalve governor related? It's been 10+ years since I owned a 2006 YZ250 2T but I feel like I remember lubing something up in that part of the RHS case with moly paste to quiet things.

My apologies if this is a wild goose chase comment, but in case not - this may jog someone's memory who knows these engines well?
Glowie
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Glowie 4/4/2022 9:01pm
4/4/2022 9:01pm
Bump for interest. Anyone determine the issue? If the crank bearing was bad wouldn’t you see massive amounts of blow-by all over the linkage and swingarm?
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Jrey2
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Jrey2 1/30/2023 11:55am
1/30/2023 11:55am

Did you ever figure out what the problem here was?

Rickyisms 1/30/2023 3:57pm
1/30/2023 3:57pm

I have to redact my prior comment about the crank bearing, although I hope OP has figured it out by now. 
 

I remember riding with my buddy on a super wet and muddy day two years ago and hearing my KTM make an identical whistling noise. I chalked it up to the bike being hot from being worked in the mud. Haven’t got to ride in a month or so but my last two times riding it’s come back. The bike still rips and feels good but it doesn’t seem to be doing any damage. Oil drains out fine and drain plug has normal clutch shavings on it. I’d like to think at this point it’s some kind of noise from a breather, either the powervalve or transmission. I replaced pipe O Rings and springs, but haven’t started the bike yet. I’d also like to inspect the water pump shaft and impeller too.  

SoCalMX70
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SoCalMX70 8/3/2024 5:37pm
8/3/2024 5:37pm Edited Date/Time 8/3/2024 5:42pm

Bumping this because my '23 makes the same noise, almost since new. About 40 hours on it now and I just did the top end... Crank felt smooth, no play in rod. Cleaned everything up real good and put it back together with a ProX piston (Japan) and OEM needle bearing. Also threw a new Bill's Pipe on with fresh O-rings and springs.

Fired up, noise still there. Just gonna keep runnin' it...

Edit: My 2016 (owned by my brother now) does not do this. That bike also got a complete overhaul in 2020 which included a new OEM crank and almost the entire transmission replaced. Still quieter than my '23 🙃

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