Knocking in lower unit with SS prop

Duckinator

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Mar 17, 2008
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I have a 2015 Suzuki 25 hp. Been very happy with it but the OEM prop is real thin at the tips and easily warped in my swamp. Been running stainless steel on my previous Merc 25s for 30 years so I bought a stainless steel prop for this motor.

I installed it and found it has a terrible knocking/rapping/hammering noise at idle speed in forward or reverse. None in neutral. The noise goes away when RPM is increased. I swapped back and forth with the OEM aluminum prop several times to verify I had it installed correctly. No noise with the aluminum prop.

The prop turns freely by hand without interference. There is clear, clean oil in the lower unit. The propshaft is straight although there is some end play if I wrestle the prop around.

Could this be a backlash issue in the gears in the lower unit that the mass of the heavier stainless steel prop causes them to rattle back and forth upon engine firing? Or something in the prop itself such as splines or hub being loose? incorrect torque on prop nut? out of balance prop?

I am concerned my lower unit has an issue but I don't think I have had any hard hits - nothing more than warping the outer 1/2" of the aluminum prop.
 

99yam40

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Sep 7, 2008
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normal with the heavy SS prop
as long as the prop is and thrust washers are tight on the prop shaft it is just the pistons firing and speeding up the prop shaft and then slowing back down again.
higher RPMs it just does not have the time to slow down
 

Duckinator

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Mar 17, 2008
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Below is a short video with the noise. Do you still think this is normal? thanks for the help.
 

Duckinator

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Mar 17, 2008
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Update: I had asked this question from where I bought it and they ran it up to Solas. Just got a phone call they are having this issue with putting stainless steel props on the little 4 strokes - at least with Suzuki and Yamaha. The will be refunding me. Evidently they have more design and development to do.
 

99yam40

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Sep 7, 2008
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not sure it is just the small motors or just solas

SS is heavier and the mass causes it to rattle
 
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