Problems with motor rattling

[Deer Slayer]

Me and my papaw go fishing a lot and he is having problems with his boat motor rattling when he has a four blade prop on and it doesn't rattle a bit when we have the three blade prop on and they are they same just that one has more blades than the other does anybody know why and how to fix this.

[Embrey]

Me and my papaw go fishing a lot and he is having problems with his boat motor rattling when he has a four blade prop on and it doesn't rattle a bit when we have the three blade prop on and they are they same just that one has more blades than the other does anybody know why and how to fix this.

if you are talking about rattling at low rpm in gear, stop running that prop until you find out what the top rpms are with both props. if this is what i think you are talking about, you are lugging the engine with the bigger 4 blade, and the sound you are hearing is the bearings beating the metal apart in the rods. what engine,prop(s) and rpm?

[imthemedic]

Another possibility is a best prop. That will definitely cause a rattling or vibration feeling.

[CTFSHWHISKER]

What are the 2props?you may have the wrong thrust washer behind the prop,example a 3bl raker uses a different washer then a 4bl renegade or shooter,does the 4blade have an interchangeable or fixed hub.

[Deer Slayer]

if you are talking about rattling at low rpm in gear, stop running that prop until you find out what the top rpms are with both props. if this is what i think you are talking about, you are lugging the engine with the bigger 4 blade, and the sound you are hearing is the bearings beating the metal apart in the rods. what engine,prop(s) and rpm?

The engine is a mercury 115 horsepower, the prop is a mercury spitfire, and the rpm runs at about 900 at idle with both props. The 3 blade prop and four blade prop are both 19 pitch and I don't know what style the prop is but mercury makes it.

[Embrey]

The engine is a mercury 115 horsepower, the prop is a mercury spitfire, and the rpm runs at about 900 at idle with both props. The 3 blade prop and four blade prop are both 19 pitch and I don't know what style the prop is but mercury makes it.

no,i mean what are you MAX speed rpms? its probably not what i said, but it should be checked out. even though they are the same pitch, a four blade in a 19 is more like a 20 in a 3 blade.

[Monarkman]

Stainless props rattling at idle on the 4 1/4 gear cases is a common problem and I have experienced it myself and goes away with a 3 blade aluminum. I know the spitfire is also aluminum but maybe the extra blade is making it do it. Mercury has a redesigned anti rattle hub kit and has been around for a while. Anti rattle is called flo-torque III vs. the II.