Merc 350 mpi vibration

rough rider

Cadet
Joined
Jan 12, 2015
Messages
27
New to me 2005 bay liner 225br. I've noticed a pretty loud vibration during tight turns while accelerating. Is this a gimble bearing problem or prop problem? Not sure I am happy with the prop I have on there now. It's a stainless three blade not sure what pitch it is. I am getting 4800 rpm and 48mph. Is this about right for the Mpi 350 5.0 motor? I am thinking of switching to a four blade for better torque while pulling a skier out of the water. Anyone have any useful input?
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
You may find your prop size under the prop nut.I'm no I/O expert but a universal joint might vibrate in tight turns.If you turn to the extremes at no wake speed it may be more obvious. If your prop is damaged it may vibrate.
An I/O expert may be along with more help.
 
Last edited:

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
18,336
You will need to remove the outdrive to gain access to the U-joints. Typically the U-joints will 'feel' OK, even when slightly worn.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,822
this is a new to you boat that you should pull the drive and inspect the u-joints, pressure test the drive, check the gimble bearing and replace all 3 bellows. If it is an alpha drive, you should also replace the raw water pump in the outdrive as well. If its a bravo, pump impeller needs to be changed (however that is mounted to the engine)
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,255
I've noticed a pretty loud vibration during tight turns while accelerating.

Ayuh,.... Generally speakin', ya shouldn't be in a Tight turn, 'n droppin' the throttle,...

No more than ya should be revin' the motor with the drive way up,....

Anything other than straight ahead at neutral trim is beatin' up the u-joints,....
The more extreme the turn or trim, the more damage to the u-joints, til they're just plain ole worn out, or broken,...
 

rough rider

Cadet
Joined
Jan 12, 2015
Messages
27
Makes perfect sense to me, thanks for pointing that out. Seriously Bondo, I didn't think about it like that.
The vibration happens when the skier falls down I back down the throttle to make a u-turn without throwing everyone out of the boat and get back into the throttle during the last half of the turn or so. It is kind of a deep vibration, not like revin' the engine with the drive up ( I admit I did that once ) . It sounds like it resonates through the entire rear of the boat.
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
18,336
Yup, u-joints or possibly the gimbal bearing. They just don't like to be operating too far out of straight alignment. Best would be to remove the drive and see what they look like. You could try greasing them , or if they look or feel bad then just replace them.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,297
Alpha 1 Gen 2 u-joints are a maintenance item which need regular replacement. Are yours the original? Inspect the bellows, gimbal bearing and yoke seal.
 
Top