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40 HP Yamaha has loud tapping sound trouble brewing

M

Mark in Alaska

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Have a pre 1986 40 hp Yamaha.

Have a pre 1986 40 hp Yamaha. Last trip out started it up and there was a knock or tapping sound that sounds like it is coming from engine block. suspect it may be a rod? plugs burning even. Any advise on whether to tear it apart or keep going. It starts easy and runs smooth as ever.
 
"probably a rod bearing. find

"probably a rod bearing. find cyl. thats knocking by compression testing, or install one spark plug at a time. turn engine by hand till piston is moving down. use screwdriver, or similar probe to push top of piston. if it has play, bearing is gone. crankshaft probably damaged too. continue running it, and you risk bearings getting into cyl; pretty much destroying motor."
 
"Scott, That is what I had had

"Scott, That is what I had had hoped not to hear, but suspected was the case. Thanks for taking the time to reply. I will try the tests you suggested. I used some oil that was all purpose 2 cycle that said it "exceeded tc-w3", may have been going for some time but that may have had something to do with it."
 
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