New stainless prop causing "knocking"

[Duckinator]

I posted this first in the Suzuki forum but thought there may be additional experts here.

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 Solas New Saturn 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.

 

[Texasmark]

It's probably "clutch dog rattle". If the Suzuki has a similar shifting system to the Merc, a heavy, high pitched prop in perfect condition will do just what you said....BTDT The clutch dog is the little hootus that the shifting mechanism slides up and down the prop shaft in selecting between FNR gears. On Mercs, it's primarily with F gear as it has the overrun clutch built in....saw toothed shaped teeth. R has a square cog and socket setup and once in it's locked in gear it can't slip in and out.

Solution is, get another prop, like the one you had or speed up from where it rattles and if going too fast, like docking or loading on a drive on trailer, alternate between N and F till you get where you want to get. I had 4 props for my last boat pictured in my Avatar. The highest pitch SS, which was also much heavier than the rest, was the one that made the boat go the fastest and what I wanted to run. Problem was clutch dog rattle so I did as I mentioned because I was going to run that prop regardless. Dropping down 3" in pitch (24 to 21P) with a lighter SS prop solved the problem but it cost me around 6-7 mph on top end and I didn't want that.

 

[Sea Rider]

Is prop nut well adjusted on shaft ? fully adjust with hand, then go to next CW shaft hole, insert split pin. Can use a piece of wood to lock prop under anticav plate while adjusting nut with wrench.

There could be slight lenght measurements differences between both prop brands ?

Happy Boating

 

[Duckinator]

Here's a short video with the sound I am concerned about. Any additional thoughts on it?

 

[89retta]

Are you able to run the engine out of water on a set of muffs? Your prop shaft may appear straight. But with the extra weight of the ss prop it could cause it to wobble more.

 

[Duckinator]

Update: I had asked this question from where I bought it and they ran it up to the manufacturer. Just got a phone call they are having this issue with putting stainless steel props on the little 4 strokes and are refunding me. Evidently they have more design and development to do.

 

[Sea Rider]

Should not install SS props on portable outboards, according to Iboats prop finder. Alum is a great choice for small and medium sized boats. SS props are ideal for large or heavy boats and those running in saltwater. Best performance is achieved on those combos running + 50 MPH.

If you swap an alum prop for a SS prop without taching second, engine surely will rev towards the lug side of its wot rpm range.

Happy Boating

 

[hemi rt]

That sure can't be good to the parts inside the gear case, I'd get it off as soon as possible