prop. question for Bob or anyone.....

[Bob Orlando]

The boat I just purchased has a brand new Mercury 40 EFI. I have never owned a Merc before and have been looking at it pretty closely. I noticed about a 1/2 inch? or so play of the prop on the prop shaft forward and aft. Is this normal for a Merc? The nut and bend over tabs are intact and the motor was demo'd for me when I picked it up.



Any one have any ideas?

 

[Bob Bourget2]

Hi Bob;

The new hub design {REFLEX} on the 731 series gearcase allows for a LOT of prop "wiggle" both fore and aft and even a little "sideways" if you can understand that. 1/2 inch is too much...should be more like 1/8". When I first saw these, I called Merc because I was flabber gassed at the amount of play. Re-check yours.

 

[Bob Orlando]

Bob B,.... I rechecked the fore and aft play of the prop on the shaft and it is 1/8" as you stated it should be. There is even a "slight " side to side play, noticeable but slight. I'm wondering what Mercury's reasoning behind this might be.



I'm not overly concerned about this now that you have clarified the situation, just curious.



Anyway, once again thanks for your time. Could it possibly have to do with their wanting to prevent "lockup between the prop and shaft due to lack of PM?

 

[Bob Bourget2]

Actually, it has to do with harmonics. The new 4-stroke motors are very smooth, and the slightest vibration is picked up {audibly}. The play in the prop is to counteract this issue. We had an issue with stainless props causing the infamous "clutch dog rattle" that was present only at idle, in gear on certain motors. Fixed by another style of "hub".

 

[Bob Orlando]

Alrighty then, I see now, ..a form of "harmonic balancing." I honestly don't know what we would do without your help on this forum. Thanks a bunch!

 

[Bob G.]

Too many "Bobs" on here!! Lucky for me, no one asks me anything!! :lol: