Light knocking at idle in gear

[DCMacGuy]

I'm slowly going through things in my newly purchased boat, and something I have noticed is that I have a knocking noise coming from the outdrive when idling in gear. There is no vibration, and everything is really smooth otherwise. Supposedly my gimbal bearing and such were replaced last year in the boat, but as I am learning - the marina from which I purchased my boat (it was a former rental there) are not exactly the most truthful bunch of people.

Obviously it's difficult to diagnose over the internet - but I put a short acceleration video up. You can hear it at the beginning of this video if you turn the volume up; it's not really that loud but my phone seems to pick it up well before the intake honk of the 3.0mpi takes over.

Don't mind the tach which is completely useless and inaccurate (another screwup from the selling marina, along with the falsified hours...). I use VesselView Mobile, and I'm getting to about 4850RPM unloaded.

https://youtu.be/0D-DuB_VeYs

 

[bruceb58]

If its a slight knock, it's normal.

 

[DCMacGuy]

If its a slight knock, it's normal.

It's pretty slight. Kind of what I thought - but it's been years since I've been in a boat with an Alpha One my ear isn't used to the myriad of clunks and thumps they make going about their business

I figured I'd let the experts on here give me their thoughts.

 

[Jcris]

First thing I noticed was the tach. Did seem very high for the speed you were going

 

[DCMacGuy]

First thing I noticed was the tach. Did seem very high for the speed you were going

It's one of a long list of screwups that the marina will be fixing, otherwise I will be pursuing legal action.

I bought the boat with the OEM tach in it in February, when I picked it up in April this tach had been installed. I am pretty sure it's just set for a V6 or V8 on the back but I am not dealing with it right now and rely on PCM data. Supposedly the OEM one is unavailable, so I'm having them replace the speedo to match it.

I was told it had 330 hours on it. I installed a VesselView Mobile module and found out the boat had 565 hours on it. The marina gave me some story about the tach having been replaced in 2014, I sent them photos of the day of purchase and the day of pickup and they had no comeback.

Lesson to be had - document everything with pictures and emails. I absolutely love the boat, but as soon as my gauges are fixed and my backordered tonneau cover is installed this will be the last they will see of me or my money.

 

[Jcris]

The motor does sound good though.
Frustrating to deal with some businesses.

 

[Scott06]

The only difference between being in gear and in neutral is the load on the prop and the propshaft turning. Would need to listen to it closely to see if it is coming from inside the engine compartment ( more towards gimbal bearing or ujoints ) or from the out drive- maybe bearing on propshaft. Gimbal bearing tends to be more of a growling typically but does it change if you steer to one lock or the other? Do you have an independant mechanic who can look at it ? Might be something easy like gimbal or unjoints but could be an issue in the drive- what does the drive lube look like out of the drain screw - metal pieces (some small pieces on magnet on screw are normal)