Engine Identification - MC18 vs. MC21

**Mon Jan 31, 2011 1:02 pm » Post: #1 » Download Post**

Previously this site helped me identify my engine using the engine number. Engine number says it is MC18 R2J. But then I found that the engine has a gear position sensor.

http://www.bikepics.com/pictures/2142437/

The MC18 has only a neutral switch. So taking a look at at the serial number again i noticed it has been modified. The old number has been ground out and a new one stamped into the engine case. The size of the numbers do not match and the aluminum has a divot you can feel with your finger.

Here is a photo of the crank.

http://www.bikepics.com/pictures/2142438/

Can this crank be verified as an MC21 via this photo?
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MC21R9N track
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CBR954
CR250

**Mon Jan 31, 2011 2:27 pm » Post: #2 » Download Post**

On the parts manual all MC21 have an o-ring on stator side of crank (located on the bearing i think). MC18 do not. My crank does not. Which is in direct conflict with previously mentioned GPS.

And what is the difference between and MC21/28R and MC21/28SE/SP crank? Tyga sells both.

I am so confused.

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MC21R9N track
MC18R2J track
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CR250

**Mon Jan 31, 2011 2:38 pm » Post: #3 » Download Post**

Hi Cangus,

The crank that you have attach in the photo can be either from a MC18 R5 or from a MC21 or from a MC28... All these three cranks use the same bearings... This is what i understand from the photo...

Hope i helped you a little...
Michael

**Mon Jan 31, 2011 5:59 pm » Post: #4 » Download Post**

Are you saying that it is not an 1988 MC18 R2K because it does not have a seperate center seal?
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**Mon Jan 31, 2011 6:09 pm » Post: #5 » Download Post**

Yeap,

this is what i see... if the crank hasn't been modified this is from a R5 or later model NSR...

**Mon Jan 31, 2011 8:05 pm » Post: #6 » Download Post**

An R5/6K & an MC21/28 crank may use the same bearings, but the cranks are not the same.
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**Mon Jan 31, 2011 8:50 pm » Post: #7 » Download Post**

There is no 60.7 x 1 o-ring on the outer race of the center bearing. And no corresponding groove on the bottom engine case:

http://www.bikepics.com/pictures/2142871/

Here the upper engine case has a lubrication groove corresonding to the holes in the center bearing.

http://www.bikepics.com/pictures/2142876/

Shouldn't the bottom engine case also have this groove?

Now i am only more confused.

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MC21R9N track
MC18R2J track
CBR954
CR250

**Mon Jan 31, 2011 8:57 pm » Post: #8 » Download Post**

In the crank picture i can see the groove of the center bearing... If the o-ring is there or not well this is another matter... The cases don't have a groove that the o-ring seats... So it's ok...

**Mon Jan 31, 2011 9:12 pm » Post: #9 » Download Post**

I will check tonight and let you know tomorrow. Thanks for your help. Very Happy

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MC21R9N track
MC18R2J track
CBR954
CR250

**Tue Feb 01, 2011 1:32 pm » Post: #10 » Download Post**

The center bearing does indeed have a groove for an o-ring indicating it is MC21/28. I stand corrected (yet again).

But just to be sure, someone could have rebuilt MC18R5K using MC21/28 center bearing right?

I understand the only other difference between MC18R5K or MC21/28 crank is web thickness. And that you can mill 2?mm off an MC21/28 crank to make it fit in a MC18 R5K. Does anyone know what web thickness' dimensions?
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MC21R9N track
MC18R2J track
CBR954
CR250