Loud Cracking Noise - Near WOT

S

sideways

New Member
Feb 10, 2014
37
Australia
Boat Info
Basic fit out.... Less holes that way :)
Engines
4.3L Mercrusier V6 190 hp
Hey Guys need some advice...

I have noticed a loud cracking sound... Like something banging the deck of the boat...

Flat Water
4500 rpm and greater
Frequency: every 3 to 4 seconds approx.

I have not had this boat very long...
Full service and inspection was completed.
Starter motor has been replaced.

Any ideas on where to start?
 
Thanks everyone,

For your prompt response.

V6 Carburetted. Thunderbolt V. No TKS..

The motor starts straight away cold or hot...
Makes all the right noises at idle and revving in neutral...
Temp is between 170 and 175...
There is no pinging or detonation from the motor...
Timing has been correctly set to 10BDTC with ICM grounded to static timing...

There is no growling or large vibrations at normal speeds..
This noise occurs only at high rpm and high speed...
There is no noise what so ever below 4000 rpm...

It is a little off putting as if it is something letting go.... if it lets go at that WOT speed... it will self destruct.

My last boat was a 50 hp Merc Outboard... (much less moving parts and power...)

I have not long had the boat and it is my first Stern Drive.
I subscribe to the 'Keep you motors well serviced, well tuned and well maintained... And drive them Hard...'
 
Have you had someone listen to it while your driving, to see where it's coming from? Like from flame arrest or or somewhere else? Only had problems like breaking up on newer mpi engines and it was the cap and rotor. You could try ignition components
 
Thanks flflatrate,

Will inspect rotor and cap tonight....

You say you have had MPI engines exihibit this behaviour.

When it occurred was it every 4 to 5 seconds.. single crack. As I have had ignition systems break down at high rpm.. but that usually results in a loss of power or at least a lot cracking and backfireing at high rpm.


 
Funny you should ask that Frank,

I found a cooler bag under the back seat with some loose bottles in it... These have been removed... :smt001

I am hoping that this is the noise.... wish i had found it last night... when i was on the water...

Would still like to explore any other possibilities... so next 'sea trial' i have some other check points if the noise still occurs.

Should I be concerned about running this motor at WOT.. It is a lot more powerful and complicated than my little old outboard.

I suppose I am trying to determine if this is the start of something failing... I have been around motors for many years..
I don't believe it is anything related to Mechanical in the Engine.

It could be fuel or ignition.... Both of these do not concern me..

I just want to rule out Drive Issues... as this is the part that scares me... Ie gimbal failure or uni failure...
Can failures in these areas cause the above symtoms..
 
I've had caps that would pop every few seconds while running wot, and others that would make the motor lose power also and break up real,bad. I doubt it is the out drive or gimble brg. I would runthe boat with someone close to the engine to try and pinpoint the noise
 
Take her out at night and run her up with the hatches open to see if you get any arcing from any of your ignition components. Watch your tachs for any fluctuations when you hear these noises.
 
Thanks flfatrate....

Have just pulled the cap.... and rotor... And the terminals in the cap and rotor look pretty dam nasty...

Also just replaced plugs... The may have put more load on the caps and rotor...

Thanks for the suggestions guys... Like i said before.. Motor issues don't scare me... Just a uni or Gimbal letting go...
 
Will replace the cap and rotor....
Head out tommorrow night with the video camera.... Good Idea Mark...
If it does fix the issue I will put the old parts back and video as reference for everyone.....

Here is some photos of the crustiest rotor and cap i have seen in along time
Rotor.jpg
 
Outdrives are pretty tough and can take quite a bit of abuse - especially with your running a V6.
Universal joints wearing out can usually be heard as a chatter or vibration when in neutral.
A Gimbal bearing going bad will usually start to groan, noticeable when idling in gear, like a wheel bearing only a deeper sound.
Just be sure to keep your signature subscription up to date :thumbsup:
I subscribe to the 'Keep you motors well serviced, well tuned and well maintained... And drive them Hard...'
Click to expand...
 
This has just come back from a $900 Service...
So after this service... I have reTimed motor, replaced Spark Plugs, Starter Motor and Now Caps and rotors...
... Hey I get the if it aint broke don't fix it... and the 'why did you replace those parts' but I would expect at least a 'We have inspected your Ignition components xyz and they need replacing...

I will be hitting you guys up for some tips and tricks for outdrive inspection and servicing in 6 months :)

I have just organised the neighbour to come out with me tommorrow night( with his go pro)... will remove all engine covers.. get some video of the condition.. Will put the old parts back to confirm!
 
I'd be inclined to take those parts you replaced to the place that did your $900 service and ask them one of two questions....

-if they charged you for new ignition parts when they did the service I'd want my money back for what they charged. No way that rotor should be rusted like that if they had recently replaced it.
-if they didn't replace the parts when they did the service I'd be asking them if they even took of the distributor cap and rotor and looked at them.

I'd also be looking for a different place for future service.
 
Gofirstclass said:
I'd be inclined to take those parts you replaced to the place that did your $900 service and ask them one of two questions....

-if they charged you for new ignition parts when they did the service I'd want my money back for what they charged. No way that rotor should be rusted like that if they had recently replaced it.
-if they didn't replace the parts when they did the service I'd be asking them if they even took of the distributor cap and rotor and looked at them.

I'd also be looking for a different place for future service.
Click to expand...

I have to completely agree with this - especially if it was a tune-up/maintenance service call.
If so, for $900 those are basic parts that should have been replaced.
 
Hey I'm not to bothered with the service or lack of....
It just reinforces why I do all my own servicing.

I just want to resolve this noise at WOT... And looking at the cap and rotor... I hope i have found the problem...:)
 
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