Hey Everyone, Well we were lucky enough to be able to take out our 34 this past Wednesday for the Blue Angels show in Annapolis. On our way back our Yanmar 3GMF would occasionally make a knocking sound. I'm hoping you guys might know what could have caused it.
When it happened: * We were about to enter into the mouth of the Magothy and I was taking down the main. My wife had the helm and yelled up saying that something didn't sound right with the engine. She throttled down and when I got back everything sounded ok. She said that it sounded like it was going to die. Like it was running out of fuel. * We kept it running slowly for a bit without issue. Then I tried to speed us up again. After about 5-10 mins it started making the noise again. To me it sounded like a loud knocking or banging sound. I immediately reduced power again and it immediately went away. Conditions: * At the time it started occurring we had about 1/8 of a tank of fuel. * Heavy, choppy waves for a large portion of our trip due to lots of power boats. However, at the time it occurred, seas were calm. * At start up after we sailed for a bit the prop had trouble opening and I had to reduce power a couple of times to get it to open. Observations: * I didn't see anything incorrect or worrysome during operation. * No leaking oil, fuel, or water. * Racor water separator doesn't show any water in the bowl. A little gunk in the bottom but not much. * When power was reduced, everything sounded normal and operated normal. Thoughts/Questions: * Could low fuel/dirty fuel/water in fuel make this happen? * Could this be more of a vibration from the prop not opening properly? If that's the case, could it be indicative of something in the strut or cutlass bearing? We have in the past had A LOT of problems with the prop not opening. * I did notice that during operation on the way back that occasionally the undulation of the waves caused some stress. I'm assuming just because of stresses on the prop. Today I filled up the tank and started it up in the slip. It started immediately and didn't sound like anything was wrong. I brought the throttle up and down and everything sounds absolutely fine. So I'm at a bit of a loss as to what to check/do. I do know that I still need to change the oil and I am planning on changing the fuel filters as well. I did notice that I am able to see the notch in the prop shaft where it meets the gearbox. There does not seem to be anything on the shaft that would indicate that it shifted at all though. Is this normal? Would love some help from some of the yanmar experts on here please. Kevin Paxton '82 34 #473 Japhys Spirit Cornfield Creek, Pasadena, MD
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