Engine Knocking-gctid826572

[Ricktrident]

Hi, I have some engine knocking at around 1500 and up rpms. I came off a 2 hour drive the night before and noticed it was louder but still got on plane and everything worked fine other than the noise. I did notice that hard banks port or starboard would change the sound and I'd hear a slight rumble for a while. So the day after the trip I noticed the knocking. I had someone check it out and they said they believe it's the gimble bearing or the u joints because the sound changes when raising or lowering the outdrive and turning the steering from side to side. They're going to take the outdrive off tomorrow and check. Could this be true? The knocking happens while in neutral in the slip, I haven't taken it out yet.

[Nauti_Mike]

What engine, drive and year?

Yes gimbal bearing can sound and behave this way.

[Ricktrident]

96 5.7 merc, alpha 1 outdrive. 96 bayliner trophy

yeah, I was stressing for a while thinking it was the engine.. lol

[Nauti_Mike]

Engine knock would either be the main bearing and typically a loss in oil pressure is observed or a rod bearing which is heard when that cylinder fires. A rod bearing can be isolated by removing the spark plug wire which results in the knock decreasing in intensity.

Since yours changes pitch by moveing the drive side to side or up and down I'm pretty sure it's the gimbal bearing.

Even in neutral the drive shaft is turning in the bearing. On the Alpha the clutch is in the bottom of the drive.

[Ricktrident]

thank you. no, there was no loss in oil pressure.

I should have came here first because on another forum they insisted it was my engine even though I told them these other things. I just needed reassurance in which I got now. thanks a lot for your input..

[Chief_Alen]

u-joints and or bearing.

[Guest]

I had, and I use past tense, had, the same engine. It had what I called a ping or a knock at above 1500 rpm and it got worse. Needed a valve job on the even side head. It did it again, BYE BYE engine. I had a Mercruiser remanufactured 357 4v Alpha installed. Motor and labor came to $8200. This is a complete drop in replacement motor.

[driz]

Listening around with a mechanics stethoscope will likely zero you in on the source of that sound. Don't be surprised if that engine sound end up actually coming from the drive as Chief said.