Slight knock in drive train when in gear at idle

[chaparral442]

Serviced the lower unit ( unit has 230 hrs), engine, greased gimbal bearing, Cranked engine on muffs and let idle- after engine warmed up- I put drive into gear forward and reverse - I hear a slight knocking noise- a slight increase in RPMS and the noise disappears

Is this normal?

 

[chaparral442]

Re: Slight knock in drive train when in gear at idle

last time out a few weeks ago zero noise- only thing I did was service lubes, install and grease prop- if my Torque wrench is out of calibration and I overtorqued would that cause the noise?

and why would it go away with rpm increase?

 

[Don S]

Re: Slight knock in drive train when in gear at idle

Might help if we knew what drive and what year your drive is.

 

[chaparral442]

Re: Slight knock in drive train when in gear at idle

sorry Don -- 2006 alpha one on a 4.3 carb

 

[chaparral442]

Re: Slight knock in drive train when in gear at idle

maybe I am over reacting- on second listen - I got out of the boat and went to the driveway and heard nothing- back in the boat and I can hear the noise slightly- it is not such much a knock - is there any normal noise ? in the transom assembly - or anywhere else that I may be hearing?- the second you increase rpms over idle it sounds as smooth as a sewing machine

 

[Don S]

Re: Slight knock in drive train when in gear at idle

It could be a noisy gimbal bearing. Has the drive been off to check for water in the bellows? Has the gimbal bearing been greased regularly, how about the coupler? has it been greased?

 

[fuzzybob]

Re: Slight knock in drive train when in gear at idle

Might be the flappers flapin at low RPM.

 

[FreeBeeTony]

Re: Slight knock in drive train when in gear at idle

Might be the flappers flapin at low RPM.

That's what I'm thinkin'.......

 

[Don S]

Re: Slight knock in drive train when in gear at idle

I've never heard the new style flappers make noise before, but I suppose it's possible. Especially if the engine isn't running the way it should be.
That's the problem with troubleshooting noise on a forum through a keyboard. We just can't here what he hears.
I've also had customers tell me there engine ran fine, only to find zero compression on 2 out of 8 cylinders.

 

[FreeBeeTony]

Re: Slight knock in drive train when in gear at idle

I agree Don.........it's hard to troubleshoot through a keyboard....no one knows that better than you or I......

I "heard" something this year also the 1st time I started the Vortec and I am pretty sure it's the flappers....only heard it at the rear of the engine inside the boat.

 

[chaparral442]

Re: Slight knock in drive train when in gear at idle

took her out and ran her for 3 hours with no issues- she ran like new - now I wondering if that is a sound that has always been there

and Don I have my Maint always done on schedule- the transom assembly was put in a year ago under warranty - a brand new merc assy