RM 125 transmission driving me nuts!!

Jakes Dad
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Jakes Dad
Edited Date/Time 1/10/2013 4:08pm
Ok I replaced the damaged gears checked the forks for wear and replaced one due to being under spec on width. The other 2 forks on other shaft spec'd fine. But I can't say for 100% they are not slightly bent, by eye they looked good comparing them to the others I have. I bought a complete transmission off ebay for an 06' this is an 07' motor. I measured the gears and they were the same (before I replaced them). I also measured the ID where forks ride and they were within spec.

The problem is it won't engage into 2nd gear without popping out. All other gears and neutral operate fine. I can hold shifter up when in 2nd and ratchet it again and it goes into 3rd and all the way up. This is when under power and all stay engaged.
Pulling the motor out for 3rd time tonight and will look closer at 2 remaining forks and probably replace them anyway since they were .003 to .004 wider than what's in there now.

My 1st rodeo with a transmission and it ain't going so well. 7 years of racing up till this point and the kid has never created transmission or clutch issues (other than grooved basket).
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motofab36
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motofab36 1/9/2013 5:12am
1/9/2013 5:12am
sounds more like the edges of the enagement dogs and/or the coresponding slots that they lock into are worn.
Jakes Dad
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Jakes Dad 1/9/2013 5:35am
1/9/2013 5:35am
I looked at the damaged gears I took out and there are sharp 90 deg edges on those, that would lead me to "assume" (he he) that the others are fine. I'll know more tonight when I take it apart again.

I really need to find out what exact part of the transmission works the 2nd gear. I honestly couldn't tell you what gear is what. I will print out a microfiche sheet. And I'll try and shift it with the shifter attached and see what happens when I move into 2nd gear.
xnationalwrench 1/9/2013 6:26am
1/9/2013 6:26am Edited Date/Time 1/9/2013 6:38pm
Like I reccommended on a earlier post Dad, check the shafts the shift forks ride on I have seen them bend or have just a tiny arc to them and can cause the problem you are having. Suzuki's used to be noted for this problem on both the RM125/250's back in the day.
newmann
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newmann 1/9/2013 6:33am
1/9/2013 6:33am
Too bad it isn't a 74-78 CR125, I could help! It doesn't take much wear on the shifter dogs or holes to make one slip out. One problem with the old Honda's is that one dog would make contact before the other two causing excessive wear due to only one dog doing all the work. A good machinist can clean those edges and properly back cut them for better engagement if necessary. Check the proper placement of all thrust washers to make sure someone didn't get one on the wrong side of a gear preventing full engagement of the two gears.

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BAMX
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BAMX 1/9/2013 11:46am
1/9/2013 11:46am
This may sound weird but are you sure that the bearings aren't super worn. Mine kept going into that false neutral from time to time. I did the same thing that you are doing and chased down gears and forks with nothing making a change. I finally swapped the bearings that the shift drum and gear sets run and my problem was cured. It is just a suggestion as my bike was SUPER used when I bought it. I believe the term clapped out is more appropriate.
wet paint
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wet paint 1/10/2013 12:35am
1/10/2013 12:35am
Check the cases where the shift forks go in( both cases left and right). The forks move in and out of the cases during shifting. If there is a burr or small piece of metal that caused the burr ( very small) in the case or on the shaft of the shift fork it will cause your problem.
Jakes Dad
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Jakes Dad 1/10/2013 11:53am
1/10/2013 11:53am
Thanks guys, I'll take the fork shafts and roll them on a piece of granite I have. I had a bunch of metal in there so I'll double check in where the shafts go also.
Jakes Dad
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Jakes Dad 1/10/2013 1:28pm
1/10/2013 1:28pm
motofab36 wrote:
sounds more like the edges of the enagement dogs and/or the coresponding slots that they lock into are worn.
WINNER!!! And yep I'm a dumbass for overlooking this the previous 2 times I had the thing apart.

Lesson learned, only way I'll get better at this stuff, don't want to be like 90% of the other guys and pay to have it done.

newmann
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newmann 1/10/2013 3:59pm
1/10/2013 3:59pm
Might want to change that shift fork that goes with that gear while you are at it. They'll end up bent from trying to force that bad gear in as it's popping out. You'll probably see some wear marks on it. Just put an old CR back together with the same issues.
motofab36
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motofab36 1/10/2013 4:08pm
1/10/2013 4:08pm
Jakes Dad wrote:
WINNER!!! And yep I'm a dumbass for overlooking this the previous 2 times I had the thing apart. Lesson learned, only way I'll get better at...
WINNER!!! And yep I'm a dumbass for overlooking this the previous 2 times I had the thing apart.

Lesson learned, only way I'll get better at this stuff, don't want to be like 90% of the other guys and pay to have it done.

WOOHOO! what do I win? lol

As Newman said, replace that fork too and you should be good to go.

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