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5 HP 4 Stroke Nissan knocking problem

S

Staven

New member
Recently when out boating my outboard started to knock, quietly at first, then louder as I turned back to the dock. I'm glad I did, because it died about 100 feet from the dock, and would not start (I only tried 5-6 pulls). It looked like the pee stream was not as solid as it usually was, but it did not stop entirely, just fluctuated in volume. It also looked like the exhaust might have been brown/black but I am not sure. I just assumed that it fried a piston, so I took the head apart and found the piston, rings and cylinder looked just fine. The valves looked OK, and the valve springs seemed strong too. Push rods are not bent, and the connecting rod looks OK too. I am waiting for the shop manual I ordered to arrive, so I have not been able to check tolerances against the manual yet. I have not yet pulled the lower unit apart, but it has tended to want to jump out of gear as long as I have had the unit, so I expect the clutch dogs are worn. I did get the Impeller out, and it looks like it could be distorted a little bit. So my question is, is it possible that the unit just overheated, and the engine clearances changed and caused the knocking? But didn't damage anything? Or what other possible explanations are there?
 
Is your model 5A2, 5B, or 5C?

It's possible that you overheated. In that case, you will definitely want to change the entire water pump kit, not just the impeller. The side clearances are critical to good pumping. Really odd sounds can come from a motor when it's running too hot.

Your shift linkage may have been out of adjustment. If so, and you have been popping out of gear, you may need both the forward (A) gear and the clutch dog.
 
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