rm125 jumpy second gear

Pepsiboy22
Edited Date/Time 1/2/2021 2:50pm
My 2001 rm125 had a jumpy second gear and seemed like it wouldn’t engage fully but when you gave it power it would run just fine, I took it apart to have a look at the transmission and found these damages, can anyone with knowledge tell me what I should replace and what’s causing the issue? Thank you




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beamer
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beamer 1/1/2021 11:25am
1/1/2021 11:25am
To start with it appears that the shim on the sprocket shaft may have been missing, the rubbing on the bearing retainer tells me it was contacting the gear which is second gear according to schematic. ( also that tab is on backwards as it should be holding the bearing into the case, bearing may be backwards in case too is should have a ridge to engage the tab at least my 250 does). Have to drill and use screw extractor to remove, with heat to melt the loctite.
Very important to reference the manual to make sure the proper shims are installed where they are supposed to. Beyond that inspect each gear and the dogs which engage them, rounded and shiny looking dogs indicate wear and they should be replaced.
I never have any luck trying to embed photos but i was looking at the schematic on Partzilla.
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sandman768
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sandman768 1/1/2021 11:49am
1/1/2021 11:49am
Take photos of the shift forks & gear engagement dogs... if it’s jumping out of gear it’s likely you have worn forks and/or gears...
Reekers
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Reekers 1/1/2021 7:34pm
1/1/2021 7:34pm
These years of rm125 are known for this. It doesn’t matter if you put brand new everything, it’ll still jump out of second after some wear. I’ve been through this and the only permanent fix was putting a 2004 transmission in mine. (2003 would be fine too I believe)
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Pepsiboy22 1/2/2021 12:47pm
1/2/2021 12:47pm
sandman768 wrote:
Take photos of the shift forks & gear engagement dogs... if it’s jumping out of gear it’s likely you have worn forks and/or gears...




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Pepsiboy22 1/2/2021 12:48pm
1/2/2021 12:48pm
sandman768 wrote:
Take photos of the shift forks & gear engagement dogs... if it’s jumping out of gear it’s likely you have worn forks and/or gears...
Pepsiboy22 wrote:
[img]https://p.vitalmx.com/photos/forums/2021/01/02/469491/s1200_FEE03197_CB5F_49EC_B8F9_9CC365C2EB70.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2021/01/02/469490/s1200_FCE641A2_45C8_4827_87CF_3614FC52A063.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2021/01/02/469492/s1200_2BDC6CFC_0232_4570_81D9_314518969719.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2021/01/02/469489/s1200_31E7B845_B49B_49C8_95C3_785E3B9A0E3F.jpg[/img]




What do you think of the wear on these parts? Which ones absolutely need to be replaced? thank you
sandman768
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sandman768 1/2/2021 1:07pm
1/2/2021 1:07pm
I would replace all the shift forks, case bearings and as many gears as you can still get new... they are worn...
Pepsiboy22 1/2/2021 1:34pm
1/2/2021 1:34pm
beamer wrote:
To start with it appears that the shim on the sprocket shaft may have been missing, the rubbing on the bearing retainer tells me it was...
To start with it appears that the shim on the sprocket shaft may have been missing, the rubbing on the bearing retainer tells me it was contacting the gear which is second gear according to schematic. ( also that tab is on backwards as it should be holding the bearing into the case, bearing may be backwards in case too is should have a ridge to engage the tab at least my 250 does). Have to drill and use screw extractor to remove, with heat to melt the loctite.
Very important to reference the manual to make sure the proper shims are installed where they are supposed to. Beyond that inspect each gear and the dogs which engage them, rounded and shiny looking dogs indicate wear and they should be replaced.
I never have any luck trying to embed photos but i was looking at the schematic on Partzilla.
You were right I was missing a part on the sprocket shaft, Thank you!
Pepsiboy22 1/2/2021 1:36pm
1/2/2021 1:36pm
sandman768 wrote:
I would replace all the shift forks, case bearings and as many gears as you can still get new... they are worn...
After some research it seems like the gear dogs are slightly worn but still usable, what do you think? The bearings do feel gritty thanks for pointing that out I’ll be replacing them too.
Paw Paw 271
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Paw Paw 271 1/2/2021 2:50pm
1/2/2021 2:50pm
It sure looks to me that this engine has been ridden mostly in the sand and it has made it's way into the oil in the trans and thus causing a lot of wear in the bearings and gear faces. I also see where the bearing retainer on the one bearing either was installed incorrectly or came loose and caused a lot of damage. This engine is in need of a full rebuild with all bearings and seals replaced as well as any gear showing wear. Otherwise you will continue to see this. Also do less sand riding or expect to do much more maintenance.

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