drive thump thump or chug chug sound

[highpowerdad]

2005 5.0GXI with SX drive, hard to describe, I am getting a light thumping or chugging sound from what I think is the outdrive. Stays the same in or out of gear - forward or reverse, and doesn't seem to change with trim position or steering angle. Only really notice it at idle speed, off idle I think there is enough other noise. Serviced the drive, gimbal bearing looks and feels good, U-joints are smooth in all directions...had to align the engine a little, but the noise is the same as before I took the drive off... any ideas... very annoying to me...

Scott R.

 

[QBhoy]

Hi Scott. What made you align the engine ? Was this as a result of some intrusive work previously? Had the noise only been since aligning ? Or have you checked alignment because of the noise ? How did you check and determine alignment was adrift ?
And just to get me thinking right...is the noise present at idle when in reverse, neutral and forward..or just in forward and reverse ?
Sorry for all the questions Scott. Just trying to think more about this.

 

[highpowerdad]

Hi Scott. What made you align the engine ? Was this as a result of some intrusive work previously? Had the noise only been since aligning ? Or have you checked alignment because of the noise ? How did you check and determine alignment was adrift ?
And just to get me thinking right...is the noise present at idle when in reverse, neutral and forward..or just in forward and reverse ?
Sorry for all the questions Scott. Just trying to think more about this.

So to walk down the questions ...

Noise was there before the alignment/drive removal. I greased the gimbal bearing and checked the u-joints...looking for the reason for the noise.

Alignment...checked it as part of pulling the drive for service, the alignment bar would not turn easy, raised the front of the motor about 1 turn on the engine mounts and it turned with two fingers... I have another post about one of the engine mount nuts being stuck...basically I was checking the alignment because of the noise.

Noise is present with the motor running, in neutral fwd and reverse, no difference - don't really notice it when cold starting, just after moving a while. no real difference with the drive angle either, hard over or straight...same noise, which is a rhythmic thumping or chugging...

Drive is a re-man...didn't make noise for the first ~50 hours...could it be the backlash on the gears, not so centered coupler? U-joints came with the reman drive, I assume they are Good, they feel fine, they are smooth, kind of easy to flop around compared to what I would think is normal on a drive shaft of a car, but they are smooth, and turning doesn't change the noise...gimbal bearing was replaced 100 hours ago, feels smooth, turns fine.

Thanks for looking into this...

 

[bruceb58]

So to walk down the questions ...

Noise was there before the alignment/drive removal. I greased the gimbal bearing and checked the u-joints...looking for the reason for the noise.

Alignment...checked it as part of pulling the drive for service, the alignment bar would not turn easy, raised the front of the motor about 1 turn on the engine mounts and it turned with two fingers... I have another post about one of the engine mount nuts being stuck...basically I was checking the alignment because of the noise.

Noise is present with the motor running, in neutral fwd and reverse, no difference - don't really notice it when cold starting, just after moving a while. no real difference with the drive angle either, hard over or straight...same noise, which is a rhythmic thumping or chugging...

Drive is a re-man...didn't make noise for the first ~50 hours...could it be the backlash on the gears, not so centered coupler? U-joints came with the reman drive, I assume they are Good, they feel fine, they are smooth, kind of easy to flop around compared to what I would think is normal on a drive shaft of a car, but they are smooth, and turning doesn't change the noise...gimbal bearing was replaced 100 hours ago, feels smooth, turns fine.

Thanks for looking into this...

You are not aligning your drive correctly. This two finger turning of the alignment bar is not how you do it. You push the alignment bar with grease on it and read the grease lines to see if its high or low. The two finger thing is just how much force it is to slide the bar in and out...not turning it.

I kinda doubt that is your problem. But would be good to get the alignment correct in the first place.

 

[bruceb58]

What made you align the engine ?

It is normal maintenance to check alignment annually whether there is work done or not.

 

[QBhoy]

It is normal maintenance to check alignment annually whether there is work done or not.

Yeah. Aware of this Bruce, for sure. But he mentions he actually had to align by moving the engine...a little more than just your yearly check !

 

[highpowerdad]

You are not aligning your drive correctly. This two finger turning of the alignment bar is not how you do it. You push the alignment bar with grease on it and read the grease lines to see if its high or low. The two finger thing is just how much force it is to slide the bar in and out...not turning it.

I kinda doubt that is your problem. But would be good to get the alignment correct in the first place.

Alright, so, the bar was much easier to push in once I "aligned" the motor, based on what you are saying, I might not have done it completely right, but I think it is closer than it was...I will have to try again next time...before I lifted the front, it was very difficult to even get the bar started...

 

[highpowerdad]

ALSO, and I will just mention it here, it might deserve its own post, Maybe it is related, maybe not. WHEN IN FWD DRIVE in the water, I get a vibration (shaking) at "fast Idle. from about 800 to 1200 RPM, the whole boat kind of vibrates (shakes), almost like I am hitting a natural frequency...it is really more of a shaking than a vibration. With the boat in neutral, it is very smooth...and when it is out of the water on the hose, it is also very smooth...the only thing that I can think of is the yoke assembly, even though it seemed fine or the engine mounts...and it was this way BEFORE I messed with alignment...

 

[bruceb58]

How does it sound when you have it in gear and have the drive full right or left.? You can also do that out of the water if you are careful .

 

[bruceb58]

Yeah. Aware of this Bruce, for sure. But he mentions he actually had to align by moving the engine...a little more than just your yearly check !

I have bought a 2017 Cobalt with only 110 hours on it. I just pulled the drive and it's WAY out of alignment. And it's not an inexpensiveley built boat like a Bayliner or Searay.

 

[highpowerdad]

How does it sound when you have it in gear and have the drive full right or left.? You can also do that out of the water if you are careful .

So it is on a lift, any testing is easy... this morning I ran it in the water , it is a louder thump thump thump when NOT in gear, doesn’t seem to mater much with steering angle or trim angle, maybe when the steering is hard over it is a little more... IN gear, it is less noticeable, but there, it does increase in speed when I increase engine speed, in or out of gear. The main difference from what I thought before was the it is more noticeable when NOT in gear. Also, it takes 30 sec to a minute or so after staring it for the FIRST time in the morning before the noise starts, so something has to loosen up a little for the noise to start.
THANKS

 

[Grub54891]

Had a similar thing on a mercruiser. It would thump no matter what gear or neutral. Alignment was good, u-joints and gimble replaced, even tried two other drives. The problem continued. We were the third shop to look it over. I moved on to a different job so I'm not sure where the issue was, but I planned on checking/replacing the coupler before I quit.

 

[ripjmk]

I had a boat with a Mercruiser 4.3 that made a thumping noise which turned out to be rotten stringers under the engine mounts, the lag bolts lost grip. All looked good but the small rocking of the engine produced a thump! A quick test to eliminate this as the source is to put your finger on the mount to stringer joint when its making the noise, if you feel ANY movement check the mount bolts. Sure hope that's not your problem though. Can you discern if the noise is once per rev, once every 2 rev or once per more revs than that? 1/rev could indicate primary drive issue, 2/rev could indicate engine firing issues less often than that could indicate lower driveline issues.
Another quick test you could do is run it with one plug lead disconnected eight times to see if one makes no difference to the way the engine runs.
It might not find the problem but it is all good information going forward.

 

[highpowerdad]

I had a boat with a Mercruiser 4.3 that made a thumping noise which turned out to be rotten stringers under the engine mounts, the lag bolts lost grip. All looked good but the small rocking of the engine produced a thump! A quick test to eliminate this as the source is to put your finger on the mount to stringer joint when its making the noise, if you feel ANY movement check the mount bolts. Sure hope that's not your problem though. Can you discern if the noise is once per rev, once every 2 rev or once per more revs than that? 1/rev could indicate primary drive issue, 2/rev could indicate engine firing issues less often than that could indicate lower driveline issues.
Another quick test you could do is run it with one plug lead disconnected eight times to see if one makes no difference to the way the engine runs.
It might not find the problem but it is all good information going forward.

Never say never, but I am pretty sure this noise is somewhere behind the motor...in the drive shaft for drive...I will double check though. As for the motor itself, it is running really smooth...no missfires...probably going to replace all of the rotating parts...unless someone can point me in another direction....gimbal bearing, drive shaft assembly and pinon shaft bearing in the drive, if it is "easy" to remove...I know that will be throwing parts at it, but then I will know for sure ...either problem solved or none of the parts replaced.

 

[highpowerdad]

So this weekend, when it warms up a little outside, I am going to do the following...

1 check the engine mounts and what they are bolted to...both front and back
2. check the drive shaft where it goes into the coupler, see if it is spinning true. I can see it from the top back of the motor
3. get a mechanics stethoscope and see what I can find with it.

I really don't think it is the gimbal bearing and I guess I would be surprised if it is the u-joints since the noise doesn't change with steering angle. I find it a little odd that it takes 30 seconds or so after starting the boat cold for the noise to start.

I am also really wondering if the noise (a rhythmic 10 hz, mostly NOT in Gear) and the shaking at about 1K rpms (ONLY in gear) are related, or if I really have 2 issues...any more ideas or things to try would be appreciated.

Thanks
Scott

 

[bruceb58]

10Hz wouldn't be a thump. 10 Hz is around the frequency of the engine RPM.

 

[highpowerdad]

10Hz wouldn't be a thump. 10 Hz is around the frequency of the engine RPM.

yes, it is a rhythmic 10 hz, 600 rpm noise, sometimes a little click like, but mostly a fast thumping, like you would think of with out of balance machines. I will try to get a recording...

 

[bruceb58]

yes, it is a rhythmic 10 hz, 600 rpm noise, sometimes a little click like, but mostly a fast thumping, like you would think of with out of balance machines. I will try to get a recording...

Well, since the drive line is spinning at that RPM, it would make sense. If your drive was REALLY out of alignment, makes me wonder about the coupler. Any metal dust in the bilge?

 

[highpowerdad]

So, I did some investigating today…the noise is NOT coming from the engine…I am 99% sure of that…used a stethoscope all over the place. The noise is in the back of the boat, drive shaft, U-joint, gimbal bearing or something in the drive…sound recordings are attached, if I can figure out how to load them.

• It took about 5 minutes after starting the engine cold for the noise to start, after that it is always there at idle in Neutral
• It is only obvious in Neutral. In gear the noise goes away, forward, or reverse.
• In neutral, it is loudest at idle, as I speed up, it gets faster, but not as loud, or maybe the engine is just louder.
• It MAYBE changes a little as I steer left and right and trim up and down, but not much…but I did make a note that it was more noticeable…
• When I first pop it out of gear into neutral is when it is the loudest.
• Boat was smooth, I did not notice any bad vibration, so that must have been something else…I did feel a LITTLE vibration at very sharp turning angles at 2000 RPM…but not bad.

What would take a few minutes to loosen up and then stay as a constant thumping in neutral. I am thinking the bearings and gears in the drive would get more lubed as it ran, so probably not that…unless someone knows better. That leaves the U-joints, which should be noisier as the steering moves – which it might be a little, but not by much…? The gimbal bearing…which I would think would be more of a “growl”? The coupler, which I would think I could here more in the engine bay? My vote is for the u-joints, but I don’t want to lead the witness…. Hopefully, the attachments work…what say you?
View attachment 2021-02-05-16-55-00.mp4
View attachment 2021-02-05-16-54-15.mp4

 

[bruceb58]

I am thinking what you are hearing is normal. Very common for Volvos to get some clatter in the top of the unit when at idle. Mine has had that ever since I owned it since 2002. Goes away when in gear out of the water when there is just the slightest amount of load.