1995 7,4 King Cobra rattling noise at idle/slow speeds

[John Scott]

My 1995 7.4 King Cobra w/o duoprop has made a rattling noise at idle in neutral and slow speeds for the last several years. This may happen at higher speeds by due to louder engine noise at higher rpm, I cannot detect it. I had a mechanic tell me last year it was nothing to worry about as it was the exhaust flappers making the noise. It hasn't gotten noticibly worse in the past several years and the drive has been pulled every other year during winterization to inspect and lube the u-joints and gimbal bearing. The boat only has 680 hrs. with no more than 50 hrs per year. Additionally, there is no remarkable vibration and any speed. Could it be the exhaust flappers or my worse fear is if it could be the u-joints, gimbal bearing or something in the drive line. Just returned from a trip wher I logged 25 miles and ran smooth as silk cruising at 28 mph. Would appreciate any thoughts on what this may be.

Thanks.

 

[bruceb58]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

Are you talking about the rattling in the upper unit in neutral? My understanding is that its completely normal and will disappear when a load is put on it in gear.

Out of curiosity, where is your raw water pump? On the drive or mounted on the engine.

 

[cr2k]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

U-joints will get nosier when you turn the drive, gimbal brg. will get nosier the higher the rpms go.
Could be the upper drive as stated or the flappers.

 

[John Scott]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

Are you talking about the rattling in the upper unit in neutral? My understanding is that its completely normal and will disappear when a load is put on it in gear.

Out of curiosity, where is your raw water pump? On the drive or mounted on the engine.

Thanks for your response. It's difficult to ascertain where the rattle is coming from as the boat has been in the water when I hear it. It is more pronounced when the bilge cover is open. The rattle is still present when in gear at idle and increased throttle. Raw water pump is mounted in the upper gear case.

1995 Four Winns 258 Vista

 

[John Scott]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

Thanks for your reply. The rattle sounds the same whether the drive is turned or not. Being that the drive has been pulled and serviced after the rattle presence I'm beginning to lean towards the flappers being the origin of the rattle. Interesting that your response included the bit about the importance of changing impellers before they fail as mine did about three years ago and shutdown engine due to overheat. Fortunately no major internal engine damage but may have melted the flappers??????????

 

[bruceb58]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

Fortunately no major internal engine damage but may have melted the flappers??????????

That is possible.

The rattle that I was thinking about is not going to heard if the boat is in the water.

 

[John Scott]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

That is possible.

The rattle that I was thinking about is not going to heard if the boat is in the water.

Thanks again for your response. Still perplexed so the boat is going to my mechanic so I can get this resolved prior to our annual trip to Ontario's North Channel.:joyous:........... I'll post the outcome.

 

[jerryjerry05]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

Try turning the motor,left and then right while in the water.
Then tilt it up a bit,no farter than you'd tilt while running.
Then again turn L/R If there is no change in the noise then it's probably the flappers.
If you have it serviced every year.
I'm sure the mechnic would point out the defective U-joints.
They make good $$$ replacing those.
From what I understand they stopped putting the flappers in the newer models??

 

[John Scott]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

Try turning the motor,left and then right while in the water.
Then tilt it up a bit,no farter than you'd tilt while running.
Then again turn L/R If there is no change in the noise then it's probably the flappers.
If you have it serviced every year.
I'm sure the mechnic would point out the defective U-joints.
They make good $$$ replacing those.
From what I understand they stopped putting the flappers in the newer models??

I do recall still hearing that the noise does not change when turning the wheel at idle speeds and slightly faster when in a no wake zone. I have also had the drive trimmed up as I would when running and the noise is still present. I suspect you're right that it is the flappers.
Thanks for your response.

 

[John Scott]

Re: 1995 7,4 King Cobra rattling noise at idle/slow speeds

Found the rattling noise...it was the exhaust flappers as I changed them out and noise is gone. Thanks everyone for your replies.