Why replace cam bearings?

Model Airplane News - RC Airplane News | Why replace cam bearings?

I want to replace the cam bearings in my OS 120 4-stroke engine.  I have replaced the crank shaft bearings but can’t get the cam bearings out.  Your help would be appreciated.

Dear Greg,
Unless it is absolutely necessary I would recommend leaving the cam bearings alone. If you do want to go ahead with the removal, you can sometimes get the bearings out by removing the cam and followers and heating the side of the cam housing with a propane torch. Then smack hard on a block of wood. Install the outer bearing plate on the engine to remove the outer bearing.

If this doesn’t work, I don’t know of any commercial Polaris that will work with such small bearings. One can be made, but access to a lathe will be required. Take a short length of brass bar stock and turn it down slightly smaller than the o.d. of the bearing. Then turn the end down to .001″ larger than the bearing i.d. Drill and tap the other end for a 10-32 cap screw.

The small end is pressed into the bearing bore. Then bore a piece of brass bar’ stock to slightly larger than the bearing o.d. and deeper than the length of the pressed in piece leaving the end solid, and drill a hole for the 10-32 screw. Slip this over the pressed in piece, heat the housing bearing area and turn the screw. The bearing should come out. A piece of tubing and a thick washer can also be sued here. To get the bearing off the pressed in piece just support the bearing on the jaws of a vise and press or driveit out. Hence the reason for the pressed in piece being smaller than the bearing o.d. to begin with.

Good luck.
Clarence Lee

Updated: July 21, 2015 — 2:13 PM

1 Comment

  1. Making a small hook out of a piece of coat hangar wire will make removal easier. flatten the end of a piece of wire and file it down until it will go through the ID of the bearing. Bend about 1/8″ of the tip slightly more than 90 degrees. Heat the bent portion of the tip to slightly glowing and then dip it in water. This will harden the steel so it doesn’t straighten out easily. Now run the other end through a short piece of broom handle and bend it over and wrap with tape or something to hold it in place. Now, heat the crankcase (NEVER with a torch) in an oven to no more than 350F and then use the hook to pull out the bearing.

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