Harold Bawlzangya Racing

Different approach to installing the crank

Since I had some downtime with waiting for the crank to be re-rebuilt, I was doing some reading on putting the bottom end together.  I came across a few items that discussed using a “slug” to install the crank in the crank bearings.  I couldn’t find any pictures of the “slug”, but people either used a socket or machined a piece that would fit in or cover the inner bearing race.

This approach heats up the inner bearing race so that it expands.  This approach also froze the crank (to install in the right case) or packed ice on the crank (to install the left case) so it would contract.  Very high temperatures were discussed, like over 400 degrees or heating the “slug” so that it was glowing red.  I had a feeling that high temperatures were needed because these “slugs” didn’t have a lot of mass and would cool off quickly.

I decided to put one of the old crank halves to the test to see how this method would work.  The big benefit I saw with using the crank was that there was a lot of mass there.  After filing down the crank so the bearing would easily slip over it, this is what I had:

cank-slug-install (1)

(Click picture to enlarge)

cank-slug-install (2)

(Click picture to enlarge)

The bearing on the “slug”:

cank-slug-install (3)

(Click picture to enlarge)

With my slug ready, I used the other half of the crank for the testing.  Since the crank half had a lot of mass, I thought I would try a lower temperature to see if it would work.  I also thought I would try to leave the crank at room temperature.  That way I wouldn’t have to worry about condensation.

I got the oven to 300 degrees and left the crank half in there for 20 minutes.  I put the bearing on my “slug” for 4 minutes and to my surprise, it dropped right on the other half of the room temperature crank.  I tried this a couple more times – once at 350 degrees and another time at 400 degrees.  Each time the bearing slipped right on the crank half.  I didn’t notice any difference between the 300, 350 and 400 degree temperatures.

crank-slug-install (1)

(Click picture to enlarge)

Slipped right on:

crank-slug-install (2)

(Click picture to enlarge)

One thing I noticed was that the outer bearing race stayed much cooler than I expected.  To make sure I wasn’t going to melt the crank seal, I used one half of my junk case  that still had the bearing and crank seal for the final test.  Once the “slug” was in the oven for 20 minutes at 400 degrees, I placed it in the case half for 4 minutes.  At the end of found minutes, I checked the crank seal and it felt like it was room temperature. Despite the “slug” being hot, it didn’t transfer any of that heat to the seal.


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