Merc 5.7L after 15 minutes running clanks and looses power??

[mcimichell]

Hello! I'm new here! I'm Massimo from Italy, I'll fill up my profile immediately, but now I'm posting this question for a slip neighbour!

My friend's 1990 SeaRay 300 with twin 5.7L we went for a run today, since some time (he says) after 15 minutes running or so starts decreasing RPM (e.g. from 3100 goes to 2900, like under higher effort) and you can hear from the back CLANK....CLANK-CLANCK....CLANCK.. not too often, but pretty hard, like if someone would bang with a hammer...
What could it be? Some bearing?
the funny thing is that starts to hit every 1 to 20 seconds delay after it's running at 3100 RPM for 15-20 minutes and if he pulls back that engine after 5-6 minutes it seems to overtake the worse and the engine goes up again...
as soon as he pulls the boat for sure he'll have it inspected... in the meantime I suggested him to have it greased in every grease point it's reachable being the boat inside the water.


Sorry for my English... I speak a better Italian

Massimo - Italy
1991 3055 Avanti Merc 7.4 BII
ICQ:51548764

 

[Haut Medoc]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

Welcome to iboats ....
Since it sounds like this condition only occurs under load, I would try to have someone drive & someone to observe & see if the noise can be localized....
That being said, i would also check for any loose accessories, .ie power steering pump, alternater, anything that might hinder free turning parts ....
I'm sure you will get more feedback....
Again, welcome!........JK

 

[Don S]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

Hi Massimo, been a while since I replied to one of your posts. Guess your 7.4's running OK?

I would sure suggest you pull the drive and check the ujoints on that boat. I've seen them where one cap came clear off, when the drive turned just right it would bang very loud while it readjusted to the new location. Actually have very little vibration. The gimbal bearing was very noisy because it was rusted from salt water, and was getting hot and really binding.
We actually caught it just before it broke the transom shield and upper part of the drive.
Personally I wouldn't even start it again before pulling the drive.

 

[mcimichell]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

Hey Don!! VEERY NICE TO SEE YOU AGAIN!!!

Yes, my 7.4 is alive and kicking and my family and I are having good times with it!
I'm still telling my friends when you recognized that my noise was due to the water flappers from the other end of the world!!! d

Thank you very much my friend, I'll tell my friend right away to pull the boat out without even loosing time to grease here and there and try again!

Thanks a lot,
Ciao, Massimo

 

[Don S]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

Yes, my 7.4 is alive and kicking and my family and I are having good times with it!
I'm still telling my friends when you recognized that my noise was due to the water flappers from the other end of the world!!! ">

It was really easy to ID the sound when you posted the video "WITH SOUND". It's a shame everyone can't do that. Haven't figured that one out myself yet. Boats are easy, computers are crazy d

 

[mcimichell]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

Update, Don!
My friend on sunday test-drived the boat with his mechanic, while the 10 minutes of the ride both the engines went just great, no sound, no bang!
The only thing he realized was that he felt he had to push a little forward to insert the gear, comparing it to the left engine, that was shifting before... it was a little looser, if you get what I mean,
So this gave him more confidence in the engine and decided to go for a 10 nautical miles ride (about 13 miles, I guess) and everything went perfectly!
On his way back he felt like on his starboard engine the clutch was slippering on a stick shift car, he told me that the engine was going up to 3400 rpm without pushing... what I think from what he told me is that the shift wasn't shifting at all... he said he didn't even hear the usual "bum" and rpm decrease when the forward gear enters...
Does this tell you something more? He told me his mechanic blamed the shifting mechanism inside the external unit Alpha one.
Thanks a lot like always to everyone that could shed some light on this!
Ciao, Massimo - Italy

 

[Don S]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

What he may be hearing is the clutch dogs in the outdrive jumping in and out of gear. The original problem may have been a worn shift cable. Too much slop in the cable motion won't let it go in gear all the way. But once it starts jumping out of gear and back in real quick the shift dogs are worn out (along with the forward gear). Probably what you meant when you said "He told me his mechanic blamed the shifting mechanism inside the external unit Alpha one."

 

[mcimichell]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

The cable should be brand new, the mechanic said it could be the mechanism inside the lower unit that is lose (???) ... the strange is that my friends asserts that putting the forward gear and accellerating a looot from idle you don't hear the normal "bump" when shifting, but it moves the boat forward slowly... that's very weird to me!!! I'll let you know!
Thanks a lot!
Massimo - Italy

 

[mcimichell]

Re: Merc 5.7L after 15 minutes running clanks and looses power??

No update yet, boat still in the water... bad wheather, maybe this weekend!
I tried it myself and I felt it's shifting just fine, a small bump when inserting the gear, the boat that slowly starts...
Maybe it's really only the propeller rubber worn out? Maybe we'll try in the water to turn the prop in foreward gear to see if it slips if we turn it backwards!
Updates coming up!!
Thanks to all!
Ciao, Massimo