Motor Bearing Removal on a Dewalt MBF

[jteneyck]

My newly acquired MBF runs very quietly and smoothly, but when I turn it off it emits a strange sound.  After 65 years it would be no surprise if one or both of the bearings needed to be replaced.  I want to give my friend a saw that he won't have to do any special maintenance on for a long time, so I decided to change them.  I've ordered them and hopefully they will arrive soon.  In the meantime, I decided to go ahead and tackle the job of disassembling the motor and pulling the bearings.  

I did this job on my GWI at least 20 years ago; long enough that I had forgotten the whole process, but not so long that I had forgotten that it was not fun.  Hopefully, older and wiser would tip the scales in my favor this time.  I started by cutting the power cord between the motor and arm so I could take it down to my shop to work on.  Smart move based on what followed.  I watched a YouTube video and read a review about getting the motor apart.  Simple, remove the four long bolts that hold the end bells to the main body, tap the front bell loose, and the armature either magically comes out of the back bell (YouTube video doesn't show how he did it) or easily pulls out (written description).  Not mine.  I got the front bell part way off by tapping the side openings with a rubber mallet, but I had to heat it with a heat gun to get it off the rest of the way.  The same strategy did not work for getting the bearing out of the back bell.  So I made a little puller from a block of wood and some 3/8" rod, and it worked great.  







OK, now for the bearings.  There's a spring clip in front of the front bearing, so I removed that.  The I installed a bearing puller against the back of the fan, with the bearing puller's flat face against the fan and snugged up tight to the flange.  The fan is made of aluminum, so you don't want to apply force very far from the arbor or you risk bending or breaking it.  Using a typical gear puller would be a really bad idea.  Why do you have to pull the fan and bearing together?  Because there's not enough room behind the bearing to get a gear puller on it, as you can see in the photo above.  



It didn't take a lot of force to get the fan and bearing off. 



OK, now for the rear bearing.  Since there's nothing behind it was easy to install the bearing puller.  But this bearing was well bonded to the shaft.  It gave a resounding pop when it finally let loose.  And as you can see, the OD of the press screw is larger than the ID of the bearing.  I solved that problem by repeatedly stacking #6 nuts under the screw as I pressed the bearing out.  





With that done, I blew 65 years of dust out of the motor windings.  Everything looks really good and ready to rebuild.  I'll add that part of the story after the bearings arrive.  

Oh, you might wonder if the bearings were bad.  The front bearing seems absolutely fine to me, but the rear one definitely feels gritty when you rotate it, so I'm assuming that one was the source of the noise.  And even though the front bearing looked good, as long as I have it apart, I might better replace it, too.  

John

[barryvabeach]

John, thanks for the photos , it really helps following your description.

[Tapper]

Nice looking work as usual, John! And yes, the pics always tell the story. Will look forward to the conclusion!

Doug