Thread: Rattling from motor

So i cranked it back up today to really tryin and listen to rattle and I have centralized it to just below the motor. Sounds comes from where my light is shinning


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Unless Sliderman knows something about that merc I don't my first inclination would be to check the bolts that hold power head and center section together. The only thing in that area that can rattle I know of would be the exhaust tuner. On merc I don't know if it is held in place by pressure from power head or if it has its own hold down bolts. Since you said it was rebuilt I'm just thinking something might not have gotten installed properly. Also did you ever check the prop hub for looseness.

Cray, the tuner does bolt up on that motor. The issue I'm seeing is that there are too many possibilities to accurately guide the owner in making a repair. Of the many things I've seen on those motors, the magnets are trouble free and if one were to come loose, it would wipe out the stator. Not rattle. The rattle could be in no certain order; loose flywheel nut, failing top crank bearing, rod bearing, piston slap, detonation, loose tuner or powerhead attachment bolt, or something coming loose in the lower unit and resonating up the driveshaft. And there's probably some more things that aren't coming to mind at the moment. Those motors suffer from an issue were small gravel or vegetation collect behind the thermostat which leads to an overheat problem. Based on what I know, his best option is to contact the rebuilder or a competent tech and have it checked out.

Originally Posted by sliderman

Cray, the tuner does bolt up on that motor. The issue I'm seeing is that there are too many possibilities to accurately guide the owner in making a repair. Of the many things I've seen on those motors, the magnets are trouble free and if one were to come loose, it would wipe out the stator. Not rattle. The rattle could be in no certain order; loose flywheel nut, failing top crank bearing, rod bearing, piston slap, detonation, loose tuner or powerhead attachment bolt, or something coming loose in the lower unit and resonating up the driveshaft. And there's probably some more things that aren't coming to mind at the moment. Those motors suffer from an issue were small gravel or vegetation collect behind the thermostat which leads to an overheat problem. Based on what I know, his best option is to contact the rebuilder or a competent tech and have it checked out.

Well I plan on check for rod knock this evening if I got time. And I pulled in and Out on prop and had bout 1/8-1/4 inch of play to it didn’t seem like much . And I figured if it was lower it could still send vibrations up the shaft to make it sound like motor. I’m not scared to break the motor down and change bearings I’m just not real good at diagnosing this issue. My first thought was a bearing possibly but like u said There are so many different things it could be.


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So got home and pulled all plugs check each cylinder and the number 2 cylinder I could push in about 1/16-1/8 of an inch when I ran it to all the at top of stroke and just passed it and could push it in a little and heard it. Other two where tight. So I’m gunna say rod bearing?


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Originally Posted by Dewdrop

So got home and pulled all plugs check each cylinder and the number 2 cylinder I could push in about 1/16-1/8 of an inch when I ran it to all the at top of stroke and just passed it and could push it in a little and heard it. Other two where tight. So I’m gunna say rod bearing?


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I would say so. Hopefully it hasn't gotten the crank.

Originally Posted by Cray

I would say so. Hopefully it hasn't gotten the crank.

The #2 cylinder is the one that he had to bore. Kind of aggravating since he was just in it not longer than 8 months ago. If it’s a rod bearing would it stop vibrating a little higher rpm than idle?


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Originally Posted by Dewdrop

The #2 cylinder is the one that he had to bore. Kind of aggravating since he was just in it not longer than 8 months ago. If it’s a rod bearing would it stop vibrating a little higher rpm than idle?


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It could at certain rpm. Since you have to pull down anyway I would check piston skirt for chaffing also or a crack around wrist pin area. You also really need to mic the cylinder for size and true and mic piston top and bottom. Hopefully he didn’t over boar cylinder.