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Two 8HP Mercury 2-cyl. 2-strokes......one rattles and one doesn't

W

whitegreg56

Regular Contributor
One is a 1995 short-shaft pull-start.
The other is a 1998 long-shaft pull-start with alternator/rectifier for battery charging.
The 1995 idles quietly.
The 1998 goes "rattle,rattle......rattle,rattle,rattle.....rattle,rattle.....rattle,rattle,rattle....and so on.
It seems to have no effect on the operation of the engine.
It's not broken....so I'm not going to fix it unless it's something trivial.
Just curious.....just wondering......
 
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Rattles coming out of a power head are not only bad news, they usually don't rattle very long before--ker-blamo!

Jeff
 
is the rattle in neutral or at low rpms in gear?if it happens in neutral i would worry about it..if its in gear and just at 800-1200? or so its just a merc...i have a 60hp that worried me when i first got it...then i noticed that half the mercs that idled past my camp sounded like that..there were some problems in the prop area on larger models causing that...it didn't apply to my motor and i have forgotten the details...
 
one is a long shaft and 3 years difference in age...i just stated my experience and observations...nothing more Jeff...to hear my 60 run in gear at low rpm on a hose us downright scary..sounds like a little man with a random hammer is in there..and i have run many motors on the ears...
 
Could be a piston slap also. Stuck rings???I would tilt it up to it's max. position,take out the plugs,make sure pistons are about halfway up in the cylinder.and fill cylinders with mercury "power tune" and let them soak for 24 hrs. Then see if you have the same problem.
 
Thanks for all that info.
It only happens in neutral, idling. It's been that way for
as long as I can remember.....at least 5 years. The engine
is used several times a week during the boating season
and has been very reliable. I guess the "Power Tune"
wouldn't hurt....Mercury recommends using it.
I may get a stethoscope to see if I can pinpoint the source.
 
Its from long shaft when not under load drive shaft rattles . put grease on drive shaft splines. Nothing is wrong with motor.Reason rattles goes away is when in gear prop puts load on drive shift....
 
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