Sudden thud while motoring

[conchaway]

Someone suggested to me that you must keep hitting manatees.

[bendriver]

I’ve determined it is the folding Gori prop. For some unknown reason it folds when it should not with a thud. I can recover by putting in reverse for a few seconds then back to forward. I’m calling Gori tech support today to understand what’s happening.

[Bill O]

Did you verify the trans stays in gear (fwd) after the thud (shaft is still spinning)? If so then, would agree it most likely the prop If it isn't spinning and it popped it out of gear would look harder at the trans. as the issue.

[bendriver]

I’m going to check for prop shaft spin today. Gori people think trans popping out of gear is most likely the issue. Either bad linkage or something internal to transmission . Hope it’s not the latter.

[Bill O]

It's most likely just a linkage/cable adjustment needed so it is shifted in gear all the way.

[C420sailor]

Verify linkage ASAP. Each jump-out brings you closer to a rebuild...

[Jon Hacking]

Possibly unrelated, but I'll toss this into the mix, just to confuse the issue more.

We have SD31 saildrives, which have dog-clutches. We had very similar clunks to yours (in reverse) on one engine. Eventually traced it down to an improperly adjusted shift-lever cable. It wasn't going all the way into gear, & eventually the dog-clutch would slip for half a rotation & catch again. By the time I could deal with it, the nice, sharp edges of the dog-clutch teeth were badly rounded from slipping. Luckily, it's not that expensive a part to replace.

You obviously don't have saildrives, but perhaps you have a similar sort of slipping dog-clutch? Just a thought, as I don't know your gearbox...

Good luck!

[nofacey]

It’s likely a stretched cable in the tranny linkage - shifter is on the edge & pops out....which would also allow prop to fold if you were underway

[Three888s]

Quick ck. Motor mount. Thud could be engine lifting out of resting spot. Would throw drive shaft out of alinement, which would cause vibration. putting it in neutral would allow it to return to resting spot. then it would act normal. unexplained is why engine shuts down.

[Three888s]

It would also explain popping out of gear, because it would change linkage adjustment to transmission,

[Don C L]

You may have solved it by now, but if it were me I'd be down there (if there is room!) with a really bright flashlight watching the engine, transmission and shaft if you can for quite a while.