I fear the answer

[Si Rey]

I have an 89 Sea Ray 220 sundancer with the Mercruiser 5.7 and Alpha 1 outdrive, first generation. When the engine is at idle in neutral I hear a "Knocking" noise when standing on the transom. I recently pulled outdrive to replace lower shift cable and checked drive shaft and u-joints for play. All seemed well and I greased the u-joints before re-installation of lower unit. I've always had this "Knocking" noise since I owned the boat for the past year and a half. I don't get the noise when in gear only in neutral and at idle. I suspect the gimbal bearing? How would I check for wear if it is the bearing?

 

[JMRuth72]

Re: I fear the answer

Can you be a little more specific as to what "knocking" sounds like? Is it metallic, metal to wood, is it low pitched, or high? Have you opened the engine compartment and listened with as little between you and the engine as possible? "knocking" can be just about anything. I would start with the engine and work my way back. Do you have a mechanics stethoscope or a really long screwdriver? If so listen to the side of the engine. If the noise sounds like it is from the inside then you have major problems. If the noise sounds like it "transmitted" to that point move more towards the rear until it get very distinct. I am thinking that worst case would be rod bearings at which point your boating season is probably over as you will need a new engine or atleast a good rebuild. Rod bearings kinda have a slapping sound to them and you should hear it fairly clearly even without the scope. It is sometimes hard to isolate noises on a engine because how well sound travels through the metal of the engine. Take your time, be patient and for God's sake be carefull around the engine while it is running. You would not believe how quickly you can get trapped in a moving belt. Do NOT wear any loose clothing that could get caught in it either. Be as specific with what the noise sounds like as you can (example: sounds like two spoons slapping together) and we will try to help you. I am pretty good with basic mechanics and know what quite a few sounds are, but I am sure that there are people on here that are better than I am. My expertise is more electrical/electronic and am adding hydraulics to that as well. Good luck and keep us posted.

 

[cheburashka]

Re: I fear the answer

Are you talking about when it's running in water, or on muffs? My pre-Alpha outdrive makes a knocking sound when I run it on the muffs, and as near as I can tell it's just the ratchet mechanism on the prop shaft vibrating through the prop. If I keep the prop from turning, the sound stops. It's quite possible that this is a normal operating noise.