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View Full Version : Loud Metalic sound????????



Diesel Dog
07-23-2006, 05:18 PM
Hi All
We were have a great day on the upper Potomac river, going along about 40 mph when we heard a metallic sound coming from under the dash. We dropped back to idle, put her in neutral and revved the motor and all sounded well. Went to get back up on plane and heard the sound again coming from under the dash. I opened the engine hatch and had Beverly slowly accelerate and we heard the loud metallic sound coming from the engine. I pulled both oil fill caps on the valve covers but the noise was not coming from there. We tried to get up on plane a few times and every time the noise reappeared. I pulled the dip stick and the oil was at the add mark. We put the boat on the trailer and now I am on the computer. The motor rev's and sounds great in neutral; when I revved it hard in neutral I thought I heard the sound when the rev's were coming back down. So what do you think we did to the old girl? Thanks, Bill and Beverly

Bigbroadjumper
07-23-2006, 06:17 PM
Exhaust leak?

Diesel Dog
07-23-2006, 07:28 PM
No it's a sharp metalic sound and only under a load. like a hammer hitting the side of the block:bonk: She rev's freely and sounds great when in neutral. I guess I will have to take a motor head down to the river and let them here the sound. She is a 71 2+3 with a 99 5.7 alpha 1 gen 2
It sounds like it's coming from deep in the block?

oldandtired
07-23-2006, 10:29 PM
Sounds like a rod to me. How is your oil pressure? Catching it now is cheap compared to popping it under load and taking the block with it. I have spun rods in the past and not heard much with no load on the engine. I have never actually snapped one and broken the block though.

Rene

MOP
07-24-2006, 09:51 AM
It is just not worth taking a chance, I would pull it, roll it over and get the pan off. Any noise is not good and like mentioned above save it before it breaks! A grand now can save you a few when it goes south!

Phil

oldandtired
07-24-2006, 11:28 AM
it doesn't make the sound when not in gear and revs freely???? wouldn't a rod or lifter or moving motor part, if it was going south make the noise all the time the engine was running????
could it be a drive/ coupler issue issue???
don't know the alpha but i had the same noise when I grenaded my uppers it went away after I removed the drive and ran the motor???

Not always. If a bearing is spun, but has not significantly deformed the rod yet, then it won't make noise all of the time just revving. Usually you will notice the loud "tock" when you bump the throttle or when you release it. If the noise is more of a "tick," then lifters and valvetrain are usually to blame. The coupler shouldn't make noise, the universals on the yoke would make a racket and induce vibration. I'll stick to the rod theory for now. Any wierd noises should be thoroughly investigated before something worse happens.

Rene

Diesel Dog
07-24-2006, 02:43 PM
Ran the boat in the driveway this morning on the hose. Motor sounded great...At low idle, in and out of gear I could hear a slight rattle or knocking coming from the outdrive. I could put my hand on the drive and feel a knocking sensation. I shut her down and drained a few ounces from the drive. The oil was black. About 10 hours ago I installed a new pump kit and drained and replaced the oil. I could rev the engine in gear and all sounds great. Thanks again,
Bill

mrfixxall
07-25-2006, 03:29 PM
Was the oil black before you changed it 10 hr ago?
if it was it wil turn the new oil black also..
its the silver oil i would be worried about,a bravo or a alpha will make a little rattle noise..
change the oil a few times to get it mercury hp lube green again and install a drive shower,,it your running a big prop on it it will get hotter then usual because you using the the prop th limit the rpm and the drive will run hotter....

i would take off the oil filter on the engine and cut it open with a pair of tin snips and make sure theirs no brass looking particals whic hwould be your rod or main bearings after babbit wares off the bearings ..

does your oil pressure on the engine seem a little higher? in most cases the oil pressure will go up higher then usual if you spun a bearing in the lower end of the engine....

also check the 4 bolts on the top of the drive to see it their loose,ive seen this on alot of merc drives the bolts just come loose..

MOP
07-25-2006, 09:12 PM
In thinking about this one and Alpha turns everything down to the pinion, oil is black quite common. Starting to look in the direction of the "U-joints" or bearing in the drive, if the gears were busted it would not be planing and running well and just making noise. You need to do more poking around before you bust it up good!

Phil