18hp tohatsu knock after stopping engine

[Impetuous]

Hi all,

im sure someone will know the answer to this one: I just bought a 2007 tohatsu 18 HP. First thing I did was change the plugs and gear oil. I then took it out for a quick test. Started fine ran smooth. Nice under full throttle. As I pulled up to the boat ramp I hit the stop button. As the motor stopped an a second or two after, there was a noticeable knock come from the top of the engine. 3 or 4 knocks. I decided to replicate this and found it changed as follows

1. It would only do it if still in gear and hitting stop button. Wouldn't do it if in neutral
2. It was less noticeable when at idle speed
3. More pronounced if slightly above idle or after just powering down and close to idle speed

help please.....I hope I haven't been sold a problem

 

[pvanv]

What is your actual model? Year is irrelevant. US 18 hp models were phased out by that time. Are you saying the motor made a sound After it stopped running? Could be a loose bolt or maybe a bad motor mount. Never had something quite like that.

 

[GA_Boater]

Don't shut the motor off in gear if you don't want to hear the knock. Shift to neutral before shutting it off. It's the dog clutch preventing the prop from driving the motor backwards and entirely normal.

 

[Sea Rider]

OB's will always knock 3 or 4 times when stopped while geared forward at slow or fast speed as water flow keeps turning prop CW.

Happy Boating

 

[Impetuous]

Thanks for the insight. This makes sense as I couldn't replicate this in the tank. I assume because there is no momentum of the boat. I'm curios however, I've had mercs and yammy that didn't do this.. It a habit of mine to leave in gear when coming to a stop and gliding into shore

 

[ondarvr]

It depends on the design of the gearcase, most Mercs do it.

 

[pvanv]

Very possible the prop is ratcheting if you are underway and just kill the motor at speed. Not what we would consider normal operation. I would describe the sound as a click, not a knock. On my sail boat, if I am sailing with the motor not running but in F, the prop will ratchet.