One thing I do every winter is check the bearings in my engines. I visually inspect them for rust and any obvious signs of wear. If the bearings are not smooth or have any rust on them, they get replaced. A bad bearing can cause a flameout and then an unplanned auto. I feel it is cheap insurance for reliable engine runs.
To replace the bearings I have the following on hand:
Obviously, the correct bearings for your engine
Leather gloves
A 3/8” diameter dowel approximately 12” long
Small block of wood (I use a 8” piece of 2” x 4”)
The engine must be completely disassembled meaning the back plate, cylinder head, piston and ring, cylinder liner, crankshaft, and carburetor must be removed. What you should be left with is the crank case with the front and rear bearing in it. Next I try to clean as much residual oil out of the crank case as possible. Now is the time to get everything ready. Some people like to put the new bearings in the freezer to make them smaller before installation. I’ve never had to do that but it won’t hurt. You need to heat the crank case to remove the bearings. I find that an oven pre-heated to 350 degrees works the best. Some people use a torch or a heat gun. I find it’s hard to get even heat using those methods. Cover a cookie sheet with aluminum foil and place the crank case on it and place in the oven for 5 minutes. (Now you know why you cleaned all the residual oil out.) After the appropriate amount of time, remove the crank case with your gloved hand and tap the back of the case on the 2” x 4”. The rear bearing will fall out. If it doesn’t, either tap a little harder or re-heat the case. I’ve never had one not fall out on the first try using this method. If you were fast with the rear bearing you should be able to push the front bearing out with the dowel. If it doesn’t come out easily, re-heat the case. It should take very little pressure to remove it. I like to insert the front bearing first. With the case hot set the bearing squarely in its opening, hold the case against the edge of your bench, and push it in until it’s fully seated. Re-heat the case and set the rear bearing in its place. You should be able to seat it with finger pressure. If not insert the crankshaft into the bearings and push against the back of the crank shaft until the bearing is fully seated. Again, if the case is heated correctly, very little pressure is needed.
Re-assemble the engine and you’re ready for another season of flying!
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