Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

B

bommerts

Cadet
Joined
Jun 15, 2010
Messages
6
Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Hello all,

I have an '09 Four Winns H190 with a Mercruiser 4.3. When it idles, in our out of the water (testing in driveway with muffs on), I hear a rhythmic "thunk" noise. When cruising the sound goes away.

Picture a coffee can full of coffee, take a wooden spoon, then thunk on the can every second or so. The sound is a little deeper than that, but that's the best way I can describe it.

Any ideas where to start?

Thanks!
 
R

rschap1

Petty Officer 3rd Class
Joined
Apr 10, 2012
Messages
95
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

How far up is the outdrive "trimmed" when you are hearing this?
It isn't running with the outdrive up beyond the trim stop is it?
That will over stress the u-joints which may be the culprit also.
Gonna guess either that or gimbal bearing from what you describe...
but not a ton to go on.
 
B

bommerts

Cadet
Joined
Jun 15, 2010
Messages
6
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

rschap1 said:
How far up is the outdrive "trimmed" when you are hearing this?
It isn't running with the outdrive up beyond the trim stop is it?
That will over stress the u-joints which may be the culprit also.
Gonna guess either that or gimbal bearing from what you describe...
but not a ton to go on.
Click to expand...

I have the outdrive all the way down and in neutral. Sorry to sound like a complete newbie: What are u-joints and a gimbal bearing? I've heard of both of these before but have no idea what they are.
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

If the steering is all the way against the lock, you could hear a noise. Might want to remove the outdrive and look at the ujoints and feel the gimbal bearing, and check the alignment too.
 
Fishermark

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,627
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Is the noise coming from the engine or the outdrive - or can you tell?

If you are not sure, you can remove the belt up front and run the engine. If the sound goes away, at least you have narrowed it down some.
 
Oshkosh1

Oshkosh1

Ensign
Joined
Jun 8, 2009
Messages
968
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

bommerts said:
What are u-joints
Click to expand...

The universal joint allows the drive shaft to articulate with the up and down movements of the sterndrive. While they are designed to have flexibility to a limited degree(ie...withing normal operating trim settings)...driving with the sterndrive in the "up"(or trailer) position puts an undesired amount of stress/wear on it.

bommerts said:
and a gimbal bearing?
Click to expand...

It's a roller bearing in the transom which through it passes the driveshaft. Forward of the gimbal bearing is the drive coupler(where the driveshaft mates to the engine), aft are the aforementioned u-joint and sterndrive.
 
B

bommerts

Cadet
Joined
Jun 15, 2010
Messages
6
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Fishermark said:
Is the noise coming from the engine or the outdrive - or can you tell?

If you are not sure, you can remove the belt up front and run the engine. If the sound goes away, at least you have narrowed it down some.
Click to expand...

It's definitely not coming from the engine.

This is all some great advice, thanks guys.
 
B

bommerts

Cadet
Joined
Jun 15, 2010
Messages
6
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Boat is 2 years old and I think I've made the mistake of starting the motor, idling, and possibly even boating very slowly in shallow water with the outdrive way up. I'm reading now that this is a big mistake. If this is true, then I suspect my u-joints may be damaged and that's what's causing the thunk noise.

Any advice on rebuilding u-joints before I take this thing apart? What will I need to do the repair?

You guys have been incredibly helpful, thanks.
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Here is a link to download the OEM service manual. http://www.4shared.com/office/2V0kM3lL/14__Alpha_I_Gen_II__Drives_91-.html?

Some reading will help you understand your complete drive and transom assembly and how it works. Might also want to give a visit to the stickies at the top of this forum. LOTS of information there.
 
B

bommerts

Cadet
Joined
Jun 15, 2010
Messages
6
Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

Re: Mercruiser rhythmic "thunk" noise when idling, not in gear, in or out of water

rschap1 said:
How far up is the outdrive "trimmed" when you are hearing this?
It isn't running with the outdrive up beyond the trim stop is it?
That will over stress the u-joints which may be the culprit also.
Gonna guess either that or gimbal bearing from what you describe...
but not a ton to go on.
Click to expand...

Ok, serious amateur mistake here. What you described was exactly the problem. No more idling or running the motor trimmed too high, problem solved.

Thanks all for your advice!!!
 
You must log in or register to reply here.
Top