1975 Johnson 70 hp Top Main Bearing

Hello,<br /><br />I went out and put the required 2 hours of low, varied rpm boredom for break-in after rebuilding this motor. I noticed a slight whining coming from under the flywheel. In the rebuild kit that I got, the top main bearing, and the two center main bearings were not included, so I cleaned and reused the original ones. Needless to say, I have pulled off the powerhead again, and replaced all three of these. The two center mains looked okay, but the top main was a bit dry (not as oily as the center ones), and I could see that it was in the beginning stages of heat damage.<br /><br />My question is what could cause this bearing to fail so quickly after rebuilding the motor, it seemed fine before. There is a little channel that I assume runs from the intake and through the hole in the bearing casing so that oil/fuel can get into it and keep it lubed. I took a straw and blew through this channel and could hear it coming out through the carb holes, so I don't think that is plugged up.<br /><br />Thanks,<br />cvlngineer

Re: 1975 Johnson 70 hp Top Main Bearing

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Re: 1975 Johnson 70 hp Top Main Bearing

From what you've had to say, the top main bearing is failing due to friction as a result of poor lubrication. I'd strongly suggest that you dismantle the engine again and thoroughly check all of the lubrication passageways. Use a peice of mechanics wire (small diameter solid wire) and pressurized air.... 100 psi or more to clean out those areas.<br /><br />One other thing..... did you clean that top carburetor thoroughly, making sure that the jets were perfectly clear? The main source of lubrication? (Applys to other carbs also)

Re: 1975 Johnson 70 hp Top Main Bearing

Joe,<br /><br />I had the intake apart a little bit ago, cleaning the reeds, and I noticed that a small hole that connects to a nipple that a small hose connects to the carb cover was plugged with gasket sealer. This hole is part of a series of passageways that connect the carb ports on the inside of the reed plate cover. I don't know if this had anything to do with it, but the port that leads to the top main bearing is also in this network of passages.<br /><br />Thanks, <br />cvlngineer