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How to change out the Worm bearing.
Courtesy of Daniel Maloney
It is very easy to do, just takes some time and patience as does any mount job really. The most difficult part really is re-installing and re-adjusting the worm block as it just takes that time and patience thing I mentioned above. Please see the below pictures. I wanted to try something different than American Bearing Works as I have had to replace many of these over the past 10 years so time to try something different (with the hope of being more durable). I will say the new bearings sure do feel amazing after installed over the old ones, we will see how long they last though, that is the major question. The Link for the new bearing are : http://www.acerracing.com  The standard bearing used by Mountain Instruments are listed here.

  1. There are tricky parts for the first-timer doing this. First and foremost,  be very careful when removing the worm block as there are brass spacers underneath the block that Larry (the manufacture of the MI-250 mounts) used to level the worm with the worm gear. You will want to make sure the worm gear is as level as possible when removing the block to prevent these brass shims from moving (falling off to the side).  Using the RA section as an example, do not attempt to remove the worm block with the RA section in its normal position, tip the section back on some pillows or something and ensure the worm gear is level first. I suggest a five gallon bucket and two peace's of two-by-Four to hold the assembly when disassembling it. It just fits. For the DEC you want to have it standing straight up when removing its worm block. Now all is not lost if one of those brass shims do move as many times there will be dirt on that back plate and you can easily see where the shim used to rest as its outline will be on the back plate still. Try your best to not have to rely on this though.
  2. As our fellow wonderful MI-250 owner "Horizontal" Mike tells about in his tutorial getting the oldham-coupler off the worm takes some force (it has green loctite on it). What always has worked best for me with minimal marring of the aluminum piece is getting a large flat-tip scewdriver and turning it against the aluminum piece and coupler, it usually breaks free right away, then you rotate the worm while you keep turning the flat tip screwdriver to move it off the worm. After the coupler is removed you will notice a lot of left over green loctite, grab your Dremel with a steel brush attachment and that will clean it off there without hurting the worm. You will need to do this as the worm cannot be pulled through the bearing with it still on there.
  3. You will need to get a dead blow hammer if you do not have one and a dowel that is the same size as the inner raceway of the bearing. I use an 7mm socket for my dowel as it fits on the inner part of the bearing without getting stuck. You want a dowel that will stay on the inner steel race is the goal. Once the worm is removed you will knock out the bearings with your dead blow hammer against your dowel. I highly recommend the dead blow hammer as just in case you miss the dowel there will be no damage done if your hammer contacts an aluminum part.
  4. You will want something that is elevated and large enough for the bearing to fall into when it pops out. I say "elevated" as this gives you something to place the part onto and large enough meaning a larger circle than the bearing housing so the bearing can fall out without any resistance. I prefer to use something wooden for this to prevent any marring of the aluminum part.
  5. Clean out all the bearings housing's as best you can and lightly coat the outer ring of each new bearing with some MP-50, the coating is so light you almost do not know it is even there. Start the bearing into its housing making sure it is level. You do not need to push hard to get it started, just enough that it stays in place without easily falling out again make sure it is started being level to the housing.
  6. Finally, you will need a press and for that I made my own (you can see it sitting on my socket set in the finished picture), it is a 1/4''/1.5'' cap bolt with a few 1/4'' washers (which match the 698 bearing's size perfectly) and a larger washer on the outside which I use on the bearing side just to ensure not to much pressure is being exerted on the inner ring by the nut. Make sure you line up the 1/4'' washer on the bearing and while holding one side still with an allen wrench you work the other side with a socket driver. This will slowly press the bearing into its housing, stop once you feel major resistance from the socket driver. You do not have to tighten hard for the bearing to be in place. The 1/4'' washer is slightly smaller that the bearing housing so it will press the bearing all the way into the housing.
  7. Once you are done re-install your worms and you will feel a major difference, free of bumps, grit, and funny strange noises (from friction).
Click on any of the pictures below to see a larger view.

Bearing Bad Raceway

Bearing with Collapsed Raceway.

Bearing with Dried Grease.

Bearing Installed.

New Bearings.
Worm block reassembled.
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