Rattling sound at Idle

[toddingalls]

Developed a rattling sound ONLY when in neutral and only at idle.
Any ideas?
Thanks!
Todd
1990 Yamaha 115 hp 2 stroke

[boats.net]

Check lower unit oil for water or metal in oil. Check compression, may need to remove heads and check pistons and cylinder. Look outboard over from top to bottom for anything loose.

[Gilligan]

rattle at idle/ Wrist pin rattle

Rattling at idle? Yamaha had a problem with small end connecting rod wear on pistons at the wrist pins. Take out the spark plugs , rotate to top dead center by using a pencil in the spark plug hole then turn the fly wheel and see if the piston starts to receed, If it feels like it is taking rotation to start down a piston has wallowed out. This is a very small amount and does not affect actual operation but will detonate at some future point and shatter the piston. Check each cylinder for end slap wear.

[toddingalls]

Changed out lower unit oil, no water in there, and only tiny metal shards in oil.
Checked compression, all 4 close to 120 psi.
Couldn't find anything loose.
The rattling sound is worse at idle, but is still there somewhat when in gear and at higher rpm.
There is a similar post on the forum with similar symptoms that turned out to be the center bearing. Does anyone know how to diagnose that center bearing? Not seeing it in my manual.
Or any other ideas?
Thanks!

[toddingalls]

The rattling sound seems to be coming from the mid section of the outboard.
Is there a way to get a visual inspection in that area of the motor?
Or any other ideas?
Thanks!

[robert graham]

Some motors have a rubber/bronze drive shaft bushing...you can drop the lower unit to look up in there to check/access it...maybe yours is broken or damaged, causing the rattle?....worth a look/see...Good Luck!