120 Mercruiser rattling noise in flywheel area

[jvr440]

Hi,<br /><br />I've got a 1981 120 Mercruiser that has developed a noise in the flywheel area of the engine that sounds like a severe metallic "rattle". I'm familiar with automotive engines and would relate the noise to a loose or cracked flexplate on a car. I've been trying to work out an occasional miss in the engine and at first it would only do it when the engine was missing, now the noise is there all the time even under load. I put a mechanics stethoscope on the engine and it's not an internal engine noise and is loudest at the belhousing area. Is there any easy way to check for loose bolts or other problems inside the belhousing? Anyone know what this noise is and can point me in the right direction to look?<br /><br />Thanks,<br />Joe

 

[Don S]

Re: 120 Mercruiser rattling noise in flywheel area

Gimbal bearing or ujoints. Pull the drive and inspect them.

 

[jvr440]

Re: 120 Mercruiser rattling noise in flywheel area

Don, I did pull the drive and the ujoints are good. I don't know how to tell if the gimbal bearing is ok, how do I check it? Everything in there looks good and is all greased up.<br />The noise was hardly noticable standing behind the boat, but very loud from in the engine compartment. Wouldn't a gimbal bearing or ujoint be loud from outside standing behind the boat too?

 

[jvr440]

Re: 120 Mercruiser rattling noise in flywheel area

Ok, I did a search and figured out how to check the gimbal bearing. Mine has a rough spot so I'll have it replaced. I'm still baffled as to why it was so noisy from inside the boat and not heard from the outside, we'll see if that takes care of it.

 

[f_inscreenname]

Re: 120 Mercruiser rattling noise in flywheel area

When you have the drive off start the motor and see if its still there. You don't want to do double the work if it is.<br />I had a friend that had a bolt back out of the flywheel. It sounded just like a blown motor. Pulled the motor, found it (to our surprise), put lock tight on them and re torqued the bolts. Never had a problem again.

 

[jvr440]

Re: 120 Mercruiser rattling noise in flywheel area

f_ - that was a good idea and I wish I had done that, but I had the head off for a valve job at the time you posted that. After I got the head back on I ran it with the outdrive off like you suggested and the noise was still there. Pulled the engine today and found a loose flywheel. Torqued them all good and tight and tomorrow it's going back together for good I hope!

 

[Don S]

Re: 120 Mercruiser rattling noise in flywheel area

I've had lots of ujoints that felt good, but turned out to be bad. ANY, even the slighetst stiff spot, catch or anything will sound really bad when on the boat, even at idle. The gimbal bearing is the same way.<br />If they are original ujoints, they are probably bad.