03 RM125 crankshaft binds when bolts are tightened

shanepillar13
Posts
3
Joined
7/5/2022
Location
Cambridge Springs, PA US
7/5/2022 5:01pm
My 03 rm125 crank is binding whenever I tighten the crank case bolts. It spins freely until the bolts are tightened down. I did not pull the cases together using the crank case bolts. The cases slid together with a push and a few taps from a deadblow hammer. There seems to be a slightly bigger gap between the case and crank on the left side than on the right. The transmission spins without a problem. The cases were put together in this order: 1. Crank and transmission into right side case. 2. Left side slid down on top of the rest. I have tried tapping either side of the crank with a deadblow, but nothing seems to work. Any suggestions?
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FGR01
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5091
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10/1/2006
Location
AZ US
Fantasy
1334th
7/5/2022 5:12pm
The 2 most likely causes are either the crank is sitting too far to one side or it is not pressed together far enough.

To check the press width, the entire width across both webs should have been measured.

Typically in a case like this, I'd put the crank puller on the left side and pull it that direction a touch and see if it centers and frees up.

Was the trueness of the crank verified before installing? A horribly out of true crank is not going to spin freely but I assume that's been checked.
1
sandman768
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5958
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3/21/2014
Location
Saratoga Springs, NY US
7/5/2022 5:52pm
I had an RM125 do this, had crank rebuilt and the shop had the web width too wide/ out of spec…. Not a fan of hitting the crank ends with a dead blow hammer….
1
40acres
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605
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7/23/2017
Location
Tomball, TX US
7/6/2022 7:47pm
I had an '04 do the same thing, years ago. Everything measured out to spec as well. I ended up putting the case halves together, then using a crank puller I pulled the crank to the left until it was perfectly centered in the case halves. I never did figure out why the crank would seemingly fit too far into the right side crankcase but it ran flawlessly through 2 top ends before I sold it. Probably not the best advise at the end of the day but I was at a point in my life where I was certainly not going to lose any sleep over it.
3
7/11/2022 12:08pm
Here’s a thing…

Are you 100% your bike is a 2003?
Have you 100% got the correct crank for your bike?

I think it was 2004 the RM125 Con rod was something like 4mm shorter and 1mm wider than the 2003 model.

Ask me how I know..

The Shop

Bruce372
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6341
Joined
4/1/2008
Location
US
7/11/2022 8:38pm
I've tightened one down light that, not too tight. Then spin the crank via the conrod and tap the crank ends with a dead blow hammer at the same time... often hear a little crack as it seats and then spins freely.
1
1
40acres
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605
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7/23/2017
Location
Tomball, TX US
7/13/2022 7:21am
Here’s a thing… Are you 100% your bike is a 2003? Have you 100% got the correct crank for your bike? I think it was 2004...
Here’s a thing…

Are you 100% your bike is a 2003?
Have you 100% got the correct crank for your bike?

I think it was 2004 the RM125 Con rod was something like 4mm shorter and 1mm wider than the 2003 model.

Ask me how I know..
I also found this out when rebuilding my 04. A previous owner slapped an 03 cylinder on an 04 case at some point. That was fun.
btroxler
Posts
145
Joined
5/22/2017
Location
Saltillo, MS US
7/25/2022 8:51am
Need to use a crank puller to insure the crank bearings are pressed against the crank correctly.

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