2019 G25, XR7 engine, "thud/knock" after take off

[Proedge]

Noticed this on my G25, not sure if it's always been there or started recently. After taking off from a standstill, the boat will have a bit of a knock/thud, almost like it's changing gears. Happens around 5-8mph or so. Do all of these boats do this? I checked for play in the prop shaft and everything seems tight. Anyone else experience something like this?

[NautiqueJeff]

I think I might know what your issue is. I had this same thing on a previous boat. It has to do with your prop shaft moving around.

Do this test. Run the boat hard in reverse, then put it in forward and take off and see if you get the clunk. If you do, slow down gently to a stop, then try going forward again. The clunk should not happen. If it doesn't, have the dealer check the shaft connection inside the boat. Mine was loose. Once tightened, the issue was gone.

If you can repeat the issue by going in reverse and then forward, but it doesn't happen if you don't go in reverse or stop hard, this is almost certainly your issue. Reverse (or a hard stop) pulls the shaft back. Taking off in forward pushes the shaft forward. There shouldn't be any movement there, and if there is, that's the clunk you hear.

[Proedge]

Thank you for your response. I will take a look at the shaft connection at the Vdrive and see if it looks loose there. I had a similar issue on my previous Mastercraft, where the shaft nut came loose and the shaft actually wore out the coupler.

[zigs]

Jeff,

You don't have a service bulletin or tech sheet on steps to check and torque specs do you? My G21 does this only after a hard reverse, and I am four hours from a dealer so I would like to take care of it myself.

[NautiqueJeff]

No, I do not. Sorry!

[Proedge]

I'm in the same position, about 4 hours away from the nearest dealer. I had a look at the nut, haven't tried tightening it yet, need to get something under the prop to stop it from turning. Not sure how many threads are supposed to be showing. Any idea?

[jpwhit]

I would try the test NautiqueJeff mentioned before messing with trying to tighten it. I wouldn't block the prop to tighten that, I've seen props get distorted doing that and you'll have the torsional twist of the driveshaft which makes it hard to tighten properly. I use a special tool that slips over the coupler with holes for the coupler bolt heads to tighten and loosen that nut.

[Proedge]

I haven't been able to get the boat out on the water, but tried tightening the nut. It was a bit loose, I maybe got a quarter turn out of it. I then looked at my prop nut and found that it had backed out a bit also. Now I don't think the prop nut was my issue, as the prop is seated solid on the shaft. But, I re-torqued the prop nut as well. Will try it out in a couple of days when I can get the boat back out on the water and hopefully my issue will be resolved. If not, I suspect I may have worn out splines on the coupler or the prop shaft, in which case it will have to go to the dealer and hopefully get fixed under warranty.

[Proedge]

Well I took the boat out and it seems the issue is gone. I didn't notice it at all anyway. zigs try tighten your coupler nut and see if that solves your issue