3.0L Mercruiser Pre Alpha - Rattling noise coming from flywheel housing.

[CableGuy1978]

Hello again folks,

I am trying to track down a rattling noise coming from my bell housing. I had recently replaced the coupler with the help of a friend who has an engine hoist. After getting it all back together, I had the motor properly aligned by a marine mechanic and the outdrive installed. I used the boat for the first day for about 2 hours in the water with no problems. I used it again for a quick ride the next day and could hear a new noise coming from somewhere. It only seemed like it was there at around 3k RPM. The next day it got worse, to the point that it was happening through a wide range of speeds, and even at idle at the dock. I assumed something had come loose and was rattling around the flywheel.

I pulled the boat, removed outdrive and pulled the engine again. Inspected the flywheel, there are no marks on it. The coupler hasn't made any contact with the bell housing or anything else either. The one big thing I did find was that a few of the studs on the rear of the motor were actually loose! The coupler had a hair of movement to it. I removed the coupler and 5 out of the 6 studs came out with the nylon locknuts still on them. Funny thing is everything seemed tight when we installed the coupler, but it appears as though they have vibrated loose.

Luckily everything looks fine as far as wear. The studs have all threads still intact, the coupler splines are perfect still as well as the drive shaft on the outdrive.

I guess my main question is what do I need to do in order to put it all back together? I am thinking about locktite for threading the studs back into the motor itself. I have also acquired a proper rear engine mount bolt kit as well which should minimize some vibration. Is there any tricks to make reinstalling the studs easier? I am worried about damaging them by using vice grips or something to screw them in. And another question that I am hoping is obvious is - is it possible that a few loose studs could have caused such an awful rattling sound. From what I have found there isn't really anything else in there to come loose.

Anyway, thanks once again for taking the time to read and reply.
Jason

 

[mariner1900]

Re: 3.0L Mercruiser Pre Alpha - Rattling noise coming from flywheel housing.

Don't use vice grips. Go purchase 2 x plain nuts to suit the studs.
Lock the nuts together on the stud and use the nuts to screw and tighten the stud in.
Use high strength loctite on the studs or they will come loose again.
Also buy new nyloc nuts as these should only be used once.
If re-used may come loose.

 

[CableGuy1978]

Re: 3.0L Mercruiser Pre Alpha - Rattling noise coming from flywheel housing.

Right on! I would never have thought of that but it makes perfect sense to use 2 nuts together like that. Just the kind of answer I was looking for. Thank you for the advice!

Jason

 

[cr2k]

Re: 3.0L Mercruiser Pre Alpha - Rattling noise coming from flywheel housing.

Did you pay ant attention to your Gimbal bearing when you had the drive off?
Could be going bad. Makes the kind of noise you speak of.

 

[CableGuy1978]

Re: 3.0L Mercruiser Pre Alpha - Rattling noise coming from flywheel housing.

Cr2k,

Yes, I did check the gimbal bearing as well. I just had it replaced when I did the coupler job as the original had a few minor rough spots. The new one is still silky smooth all around. As well, the coupler and spline shaft show no signs of wear. Everything looked normal inside bell housing as well. I was expecting to find shiny abrasion marks or something in there.

The only thing I found wrong inside the bell housing was the loose studs holding the coupler and flywheel. So I have picked up some Locktite, and a proper rear engine mount bolt kits so I will reassemble everything and try running it on the muffs to see what's up.

It did sound perfectly fine when I first put it in the water after replacing the coupler, and I know the nuts were all torqued down on the coupler as well. I never noticed any loose studs then either. So I am hoping this is the problem.

If not, at least I have easy access to a hoist in exchange for a box of beer, and I am getting fairly good at taking this all apart and putting it back together now too!

Thank you for the reply,
Jason

 

[CableGuy1978]

Re: 3.0L Mercruiser Pre Alpha - Rattling noise coming from flywheel housing.

Hello all....

Not sure if this will help anyone else, but if it does then it's worth the post.

I have solved the rattling problem in the bell housing. After pulling the motor, removing the coupler, fly wheel, and the other 2 studs that didn't fall out on their own, I picked up some locktite blue (not the permanent stuff) and some turpentine. I cleaned the six studs and the threaded holes in the crank to remove any grease and oil. I reinstalled each stud with locktite as per mariner1900's advice with using 2 nuts to create a suitable wrenching surface. I reinstalled the flywheel and coupler the next day, and reinstalled the engine and outdrive.

The noise is gone! Which now leaves me free to address some of the other issues with this boat. However, I never thought that a 'hair' of play on the coupler, and studs that barely moved in their spots could create such an awful rattle inside the bell housing. But, that being the only fault I could find and fix seems to quiet things down again.

Hope this will help anyone with a similar problem

Thank you to everyone for responding, and for the invaluable input and advice!

Jason