Mercurcy 115 saltwater ss prop rattle

[redheadedstepchild]

I was hoping that someone out there is also having the same problem i am with my 115 four stroke. I bought the motor new, runs great trolls great, but I want a little more proformance from the motor. So I bought a ss prop for it. Hole shot was much better and top was better. The only problem is that when I try to idle into the dock or idle slow with, the prop rattle is so bad, I am afraid to use, because I my damage the engine. The engine runs great with the stock alum. prop. I sent the prop to the manufacture they found that the prop was defective, fixed it sent it back to me. Nothing changed. I am using a flow troq 3 with the prop, it helps but not enough. I was hoping that someone else had this problem and found a solution to it?

 

[Chris1956]

Re: Mercurcy 115 saltwater ss prop rattle

Are both props the same pitch? Is it possible that the SS prop (with it's higher pitch or better bite) causes the motor to miss a bit, causing the rattle?

What did the OEM say was wrong with the prop, that they fixed?

 

[Faztbullet]

Re: Mercurcy 115 saltwater ss prop rattle

Are you torquing the prop nut to specs? Are you using the prop washer that came with kit or the aluminum props washer? If not it will rattle at idle and sometimes clunk going into gear as the S/S is so heavy..

 

[Texasmark]

Re: Mercurcy 115 saltwater ss prop rattle

I wouldn't expect this problem with a 4 stroke, but could be. I have heard that they are very smooth idlers.

I have a 3 cyl 2 stroke, 90 hp. When the cylinder goes bang, there is a pretty good impulse of energy and with only 3 cylinders they are pretty far apart.

I have run 3 props on this engine, all the same brand and all SS, and only the heaviest with the most pitch makes the noise and the only time it does it is F gear up to about 1000 rpm (Idle is spec'd at 675). Docking or loading on the trailer is when this nuisance is apparent.

The F gear clutch on the propshaft in the lower unit has an overrun feature that allows you to decelerate the engine (like coming off plane to go into the no-wake zone) to a speed lower than that at which the prop is turning. As the prop rotates over this "sawtooth if you will" the clutch makes a popping noise as the teeth slide over each other. The name of it is "Clutch Dog Rattle".

Will it hurt anything?

Considering that each and every time you are in F gear and the prop is turning faster than the engine, your clutch dog is rattling. On a Sunday afternoon skiing trip, this pop could occur 10,000 times. Thing is, you usually don't hear it due to other noises that mask it, but when at low rpm's and slow speeds with a quiet engine, with intermittent power pulses to the prop, you can hear it. I never had the problem on my 6 cyl 2 stroke with the same pitch and kind of prop.

The teeth on the gears are hardened steel and if you don't think they are hard, try machining one or grinding on one. BTDT.

Do I do it? No, because I don't like the noise. I can get around it by just moving back and forth between F and N when it's a nuisance.

You can hear what I am talking about (with the engine off) by just putting the shifter in F and rotating the prop by hand. In one direction you get firm resistance, the other direction you hear click, click, click as you rotate the prop. That is what I assume you are hearing.

Anything else and my comments don't apply.

HTH

Mark