Intermittent rattle on mercruiser 120

[dryland boater]

Got a older starcraft 22 ft with 120 merc. Never made a sound till i had the engine out to replace the drive spline on the engine. Took much care to ensure everything was by the book. After startup i get am intermittent rattling noise from rear if engine. Sometimes its there. Sometimes no sound at all. Seems to come and go. Sounds like something bouncing around and no solid rattle. Anyone have any ideas?

 

[GA_Boater]

Welcome aboard.

While the motor was out, did you see an exhaust shutter? They sometimes rattle at idle and the sound goes away at a fast idle.

 

[Bondo]

Ayuh,..... Welcome Aboard,..... Another possibility is if it has the ole tin flywheel cover, 'n a screw is missin', it'll rattle,.....

 

[CamaroMan]

If not the dust plate or bolts as bondo mentioned, I just rebuilt one.. after letting off the throttle it would make a rattle sound, but not tinny. #4 bore and piston equaled 13 thou clearance (around 4 times the factory spec) on the large side of piston.. after boring it was gone. Compression was still good however but quite a bit of blowby..

 

[kenny nunez]

Another possible cause, check that the bracket that stabilizes the starter is tight against the engine block.