weird noise when on the muffs

[dgopetactical]

88 mercruiser 5.7 alpha 1

I bought this boat in april. other than little things the boat runs good.
when I put her on muffs and I get around 1,500 rpm I just dont thinks it sounds right it sounds like a grinding noise (Brawwww) or like running a peice of wood i a picket fence comming out of the exhaust.(hard to explain).I sounds like it gonna blow up if i would take it above 1,500(which I was informed not to do on other post.
I have heard other boats on muff when they rev and they dont sound like this.

The guy I bought it from did not even flinch when it was on the muffs when I bought it so I figured it was normal. At idol its sounds fine It runs good in the water im missing 300rpm at wot but Im working on that withs dons list.

is this sound normal any ideas.
I grease all visiable fittings.
all fluids are clean and have been changed in june.

And yes it is out of gear when doing this.
Thank you

 

[dgopetactical]

Re: weird noise when on the muffs

Bump

 

[bomar76]

Re: weird noise when on the muffs

If you are running the engine w/ drive in trailer up mode, you will hear all sorts of interesting noises......one of which will be the ujoints flying apart.

If not, pull the drive (6 nuts and the ram clip) check condition of ujoints and gimbal bearing. While it's off, closely inspect bellows and check alignment.
ANY rust, play, roughness means you needs to replace. A bad bellows will leak and destroy all the above and sink yer boat.

 

[dgopetactical]

Re: weird noise when on the muffs

I did it in the trailer up mode. I guess i wont do that again. I hope I did not hurt anything. Just did it for a sec it did not sound right and i backed down.
Thanks for the info

 

[Bondo]

Re: weird noise when on the muffs

Ayuh,.........

Then that Noise was the U-Joints Screaming for Mercy.....................

 

[dgopetactical]

Re: weird noise when on the muffs

Boy Im glad i stopped when I did. Like i said It runs fine so I hope I did not kill anything. When I winterize I will have all that checked.
Thanks for the replys, I learn from all my mistakes which have been alot lately

 

[bomar76]

Re: weird noise when on the muffs

Never ever ever run the engine w/ drive in trailer up ..... idle, 6,000 RPM, what ever.
Never ever ever.

 

[QC]

Re: weird noise when on the muffs

A lot of boats have trouble getting the drive down below the "trailer" or "tilt" range and safely into the "trim" range on the trailer. Don't be afraid to go down in little bumps and actually slightly (softly) hit the concrete . . . Then just bump the trim up slightly and you'll have the lowest safe spot for muffs (no contact with the concrete). Also, don't forget you can lower the front of your trailer for some help too . . .

 

[rude50]

Re: weird noise when on the muffs

I'm no expert but... while my alpha drive was off I was curious about what the u-joints would do at trailer position. So with the drive on a stand, I secured the input shaft with a make-shift yoke at the full up angle of my boat. I found that they spun close to conflict but still with ease. This did not take into acount bell housing or bellows interference. None-the-less I avoid running it in any position beyound the limit switch for no other reason than i gives me the willies.

But after my experiment I would say that since it apperears to run so close to self interference at that angle that any slop in the joints, drive input bearings, gimble bearing or even engine alignment might cause a noise like you discribed. A flabby u-joint bellows would hit the joints at an acute drive angle as well. Check them all and avoid extreems.

The u-joints do run close to the drive bearing keeper ring and the inside of the bell housing. Any u-joint slop will result in metal to metal contact and noises that will haunt you in your sleep but would most likely increase with load.

Do you still hear the noise at lower angles? Try having a good friend run it to the four corners; full down, full up limit switch stop, hard a-port and starboard in gear at a similar but safe rpm while you listen. Does the sound change with angle? BE SAFE. don't run it aground or into you and dont pull the muffs off.

With my alpha I notice a "momentum bump" at certain rpm's while on the muff. With each beat of power from the engine the drive gears are "bumpped" to the end of their lash / slop and then the preloads and friction slow them till the next engine beat. At idle I can hear the gears bumpping as a slight ringing sound from the prop. The sound at about 1200 rmp sounds a bit like you described but goes away under load, in the water, or at higher rpm's on the muff. It can be more of a tink tink tink sound at low rpm. and not too allarming.

Is your sound more of whirl, or very rhythmic, or non rhythmic? Carefully touch the drive while you hear the sound. Do you feel anything that matches the sound's frequency? Carefully use an auto stethoscope to probe the transom plate, u-joint bellows, and drive unit in several places. Do you hear anything that matches the other sound?

 

[dgopetactical]

Re: weird noise when on the muffs

I have always ran in the trailer up position (on muffs) I did not know better. I have even seen it done at a dealership when I was testing a different boat and thought it was ok. I will no longer do that. I have yet to run it on muffs in the down position. I guess rytmatic would fit. Not a nice rythem. I only ever tried to rev it 1 time mabe 2 then stopped. every week I would start it though and let it idol in trailer up with no noise at all. I will never nerver never do that again. I do not hear and noise when on the lake. And it runs fine to date. Like I said in the preveous post I will have everything checked out when I change my impeller in a few weeks. Im going out next week then calling it a season, because I have a few other things to work on the boat also before the weather craps out.
Thanks
Dennis

 

[rude50]

Re: weird noise when on the muffs

I re-read your wood in the fence deiscription and you may have had ujoint / bearing retainer ring contact (u-joint slop required) or just ujoint / bellows contact. I'd pull the drive to check everything. It's only a gasket, six bolts, ram rod bolt, a few onces of grease and a few beers away. Such is the price of peace of mind.

 

[rude50]

Re: weird noise when on the muffs

If the sound is more like the wood & fence and less grind, and is indeed comming from exhaust..... Water shutter? A metal water shutter may even add the grinding tones. But a broken or loose shuter sure would make a "wood across a fence" noise. And be rpm and in/out of the water dependant.

 

[Have Fun Today]

Re: weird noise when on the muffs

One possible source of the noise: I think sometimes the prop can spin, even while not in gear. If the prop contacts the muff bracket, this could make the noise you described. I always connect the muffs from the front and make sure everything is clear of the prop.