Mercruiser 4.3 mpi rattle when stopped

[QBhoy]

Evening all

Any ideas what this noise is when engine is shut down ? Almost thought it was the lifters or flappers...but listening again. Not sure. Coming from top end and perhaps the rear. Hard to tell. Doesn’t do it when running all through the rpm range all ok. Just when shut down.
Any opinions welcome.

https://photos.app.goo.gl/G8EuMpoLTHooG22r7

 

[Rick Stephens]

That's the dilithium crystals recharging in the warp engine nacelle.

 

[QBhoy]

That's the dilithium crystals recharging in the warp engine nacelle.

Haha. That was number 3 on the list to check Rick. I’ll make it the priority. Haha.

 

[alldodge]

The motor rocking to a stop. Motor shuts down, spark stops, a couple cylinders with compression builds then rocks the motor back to a stop

 

[QBhoy]

The motor rocking to a stop. Motor shuts down, spark stops, a couple cylinders with compression builds then rocks the motor back to a stop

You think so AD ? I haven’t heard it on my mpi, that I can think of. Quite a racket when in the flesh next to it. You think it’s ok ?

 

[alldodge]

I think its fine. Its a 6 cyl so there can be a bit more rocking because there is less cylinders. A V8 would have less

 

[QBhoy]

I think its fine. Its a 6 cyl so there can be a bit more rocking because there is less cylinders. A V8 would have less

Thanks as always AD. Maybe being paranoid, but I might even think I can hear it a little when it’s running. Like a hollow knocking off of a casing or something. Didn’t hear it at the time. But think I can in video now. Bit of a worry for him. He won’t sleep well until he knows.
I think tomorrow we will see if it does it when cold. See what happens.

 

[GA_Boater]

Boy, those Inertias are noisy buggers. :drum:

Agree with AD about the compression settle down and kickback. Watch the belt(s) and you'll a little rock back. Some are noisier than others.

 

[Lou C]

Ok listened to this carefully a few times, it seems to be making a similar noise while it’s running but when you shut it off you hear it more due to the lack of the rest of engine running sounds. Timing chain play? Valve lash? I think late model 4.3s have a non adjustable valvetrain.

 

[QBhoy]

Ok listened to this carefully a few times, it seems to be making a similar noise while it’s running but when you shut it off you hear it more due to the lack of the rest of engine running sounds. Timing chain play? Valve lash? I think late model 4.3s have a non adjustable valvetrain.

Agree Lou. I didn’t hear it when running when I was taking video. But can when listening to it now. Yeah it’s a 2008 mpi 4.3. I’m going to try it when it’s cold and see if it does the same. Thanks for replying.

 

[QBhoy]

Boy, those Inertias are noisy buggers. :drum:

Agree with AD about the compression settle down and kickback. Watch the belt(s) and you'll a little rock back. Some are noisier than others.

Haha GA. not bad...but alas...this isn’t my boat. It’s a friends regal 1900 and a tempest on it. Just had damper replaced on it there. But seems to be coming from the top and or rear of engine. I think.

 

[harringtondav]

Is this something new/recent? New noises may mean something has changed.

 

[QBhoy]

Is this something new/recent? New noises may mean something has changed.

Hi. Thanks for taking the time to reply. So, the boat was purchased late last year. Only a brief test run on the day. We both don’t recall hearing the noise then. She was then winterised and kept ashore until now. Upon first starting on the muffs for service the other week, we noticed the vibration damper was bad. Replaced this and launched today. Ran very well, apart from hearing this when we stopped it at the pontoon. So only ran it on two occasions including today.

 

[Lou C]

If you don’t have one pick up a mechanic’s stethoscope. They really help with localizing noises. After I did my top end overhaul 3 years ago I would occasionally hear what sounded like a knocking noise. Drive me nuts till I found it; port exhaust flapper! I changed the exhaust system at the same time from the original OMC one piece units to the later style 2 piece exhaust. These have larger water passages and water flow through them is different which caused the flapper to make noise. Maddening till I found it with the scope!

 

[achris]

Mine does the same. It's the balance shaft gears rattling. There's a very slight backlash and that gets 'amplified' as the engine is varying speed, even slightly. Due to the inertia of the shaft, any change in engine speed (up and down) will 'rattle' those gears... And added to any timing chain deflection, you hear it... Completely normal...

Not heard on a V8 because.......... no balance shaft.

Chris......

 

[Lou C]

good to know its normal!

 

[QBhoy]

Mine does the same. It's the balance shaft gears rattling. There's a very slight backlash and that gets 'amplified' as the engine is varying speed, even slightly. Due to the inertia of the shaft, any change in engine speed (up and down) will 'rattle' those gears... And added to any timing chain deflection, you hear it... Completely normal...

Not heard on a V8 because.......... no balance shaft.

Chris......

Hi Chris.

Thanks so much for the reply. Really appreciated it.
Im sure that will put his mind at rest. And good point about the V8

Thanks.

 

[QBhoy]

All. Sorry to bring this up again...but I’m just not totally convinced about this engine. The owner certainly isn’t convinced and has asked me to post again on it.

So not to cover old ground but this defo wasn’t making this noise when he first got it, or when we serviced it a couple of weeks ago. Since then the only thing that’s changed is that it’s has the harmonic balancer damper replaced, after noticing it had moved a little and the rubber perished. I originally thought perhaps the difference is thay now it’s doing its job and wasn’t before..making me tend to agree with the above explanation. But since then it now seems to do it when the shift interrupter is activated coming out of gear etc. I can understand why it would do that perhaps, but it seems to be getting a little more noisier and having listened to a few other similar engines..they don’t have such a prominent noise from them. I’ve just watched a link to another engine like it, which he sent, on YouTube (not something I tend to go by really, but hey) with the exact same noise. He explained it as being the valve lifters. I honestly don’t think it’s that at all. But the video shows the same noise. Best way I can describe it is like marbles rattling around a tin hollow casing. Can it be coming from the bell housing area or something ? He has now stopped using it for worry and left the keys with the mercruiser guy. Anything else it can be guys ? Sorry to question your opinions, but felt I had to. Just doesn’t seem normal to me
This is the link to the engine that makes the same noise as my friends. It’s not valve lifter though as the video is titled. Pretty sure of that. I know what they sound like. Just thought I’d add the link in case it adds any thoughts around it.

https://youtu.be/sWz6MhTsItY

Cheers.

 

[alldodge]

I don't hear the same noise from both motors, but hey I'm old

The other motor sounds like it has oil pressure issues and needs to get the rpm up to pump up the lifters. When the vlave cover off there should have been oil splashing are and I didn't see much

 

[achris]

.... Since then the only thing that’s changed is that it’s has the harmonic balancer damper replaced, ....

Always a gem hidden somewhere.

With that bit of information, I'm going to postulate that something is loose. I'd be looking at balancer bolt, crank pulley screws, anything else that was loosened in the process of replacing the balancer.

Chris......