My starboard #6 drive prop loosens after a long run. The drive spins left and that seems to be the problem. The prop gets only slightly loose with enough play to wiggle on the prop shaft and it does set up a vibration at idle speeds and getting on plane. The port spins in or right and would be constantly tightening itself so doesn't create a problem. Thanks for any imput. Doug

I have a single engine with #6 also turning left and have never had the problem you're describing.

We had the same problem with our 38 Top Gun. I threw the old nuts away and bought new ones and we've not had a problem since.

Pwrbt33
Offshore Performance
1-877-GOFAST1
410-827-0200

My Slingshot has Speed Masters. I change the nuts every season and torque to factory specs. Never a problem

Sounds like the nylon in the nut has lost it's ability to grip the threads on the propshaft.
Like the other members have already stated, try a new nylon stopnut.

I had same problem last yr, but on Bravos. This spring I used new nuts and all has been good. Not sure how it always came loose with the nut always locked in the splined keeper. I don't think prop rotation has anything to do with it since the force is always pushing the prop forward against the thrust washers, 'cept when in reverse. Ya ain't doing any high speed reverse runs, are ya?

Thanks guys, I have replaced the lock nut but since they are much cheaper than props I'll replace with a new nut before the weekend run. I try not to do many high speed runs in reverse but with blower motors around the docks it does happen. thanks again guys. Doug

Try shaving down two nuts to place two nuts on the shaft. Tighten them against each other, and they will not come off.

also ck. the shaft for wear on the threads sounds like nylock is not grabing for some reason