Thread: Prop chatter

It isn’t normal at all. I would check to see if the prop nut is torqued to specs. If it’s under warranty I would contact the dealer and let them determine the issue. JM2C

I torqued it to the specs, did not happen until the first oil change on lower unit, but I have taken the prop off about 5 times, put it together by the mechanical prints and torqued it down, but still have a little chatter at low rmp, but about 1000 rmp everything’s fine.

Here's "prop chatter" as I understand it. If you were to look at your prop shaft when it was rotating, you would think that is is turning the same speed all the time. However, your prop shaft is actually moving in "increments" throughout its rotation. The "increments" are from each of the cylinders firing and turning the prop shaft throughout its complete revolution. A 4 cylinder engine would turn the prop shaft in 4 increments and a 6 cylinder engine would turn the prop shaft in 6 increments to complete the revolution. Two cycle engines are less prone to chatter as they fire every crankshaft revolution thus why chatter is more prevalent now with 4 strokes than in years past.

Prop chatter is most often seen on smaller engines with heavier stainless props. As you can imagine, a heavier stainless prop will be a bit harder to move due to its weight (and then slow faster as it loses velocity from the friction of the water in which it is moving through). So, what you understand as "prop chatter" is the speeding up and slowing down of the prop as it makes its way around in one revolution in 4 increments (or 6 increments if it is a 6 cylinder).

The "prop chatter" is mostly seen at lower RPM's because of the greater amount of time it takes for the prop to make 1 revolution within the 4 increments. As you increase RPM, the sound becomes more uniform and the prop has less "time" to speed up and slow down, so the "prop chatter" is eliminated and not noticeable.

Changing hubs can also eliminate the "prop chatter" by providing more "cushion" at the lower RPM's, which eliminate the audible "chatter" by the incremental moving of the prop on the prop shaft.

Larger displacement and greater number of cylinders can "smooth" the increments of the prop rotating on the shaft, so "prop chatter" is less noticeable on larger engines.

Hopefully, this makes sense.

If your prop has a replaceable hub kit, a Flo torq 2 style is probably what's in it. Since it pretty rigid it transfers the chatter directly. If you want to eliminate the chatter completely a flo torq 4 has more "give" in it and should suppress the noise.

Please let us know what you find and how you fixed it. I've heard installing the washer backwards adds a little slop too and can cause the chatter. Jus sayin.....

Chris

After reading this I though my washer was on backwards, pull the prop off then started up engine and no problem then, pulled up mechanical drawing and put everything together according to drawing and still have same problem. I don’t think you can put washer in backwards, because shaft has a taper and washer in cut with a taper also to fit.

What engine and prop are you running? Without that info, I just took a stab at what you may have done during the lower unit oil change and what mistakes I've heard others do. My thought was you may have pulled the prop and lubed the splines during the oil change.....

Originally Posted by NCkenner

What engine and prop are you running? Without that info, I just took a stab at what you may have done during the lower unit oil change and what mistakes I've heard others do. My thought was you may have pulled the prop and lubed the splines during the oil change.....

it’s a 2023 mercury 75 hp 4 stroke

Sorry forgot to tell you it’s a stock aluminum or cast prop.

An aluminum prop is lightweight and shouldn’t chatter. I agree with Buckeye, it should go back and be repaired under warranty.
Please let us know what occurred as that’s odd for sure and one to know about in the future as there’s a lot of those out there.


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