Have run out of things to try with prop nut backing off !!!!

[dls]

2020 Mercury 250 Pro XS ser. #2B743128
For some time now I have been trying to eliminate my prop nut from backing off the prop shaft. I contacted Mercury and the associate was very helpful. However he personally had not heard of or seen any bulletins addressing this. His first suggestion was to replace the nut and washers which I told him I had done but the results was the same. He did find some notes where before torquing the nut to tap prop with a plastic mallet to ensure the prop was seated fully on shaft. So I removed the prop and the hub. I thoroughly cleaned everything, from the edge of the seals to the end of prop shaft, including the washers and nut threads. I then applied Mercury prop grease to the splines as outlined in the manual, taped prop with plastic mallet to ensure it was seated, assembled washers in the correct order and torqued nut to 55 ft. lbs. I marked the nut and end of shaft with a sharpie in a straight line. I went to lake, launch my boat, tied it to the dock about 10 feet away. I parked my truck went back to my boat and got a phone call with an emergency at home. I put my boat back on the trailer and of course I had to use the motor to get it to the bow eye. The motor rpms probably went up to around 2500 or so. The picture below shows exactly how much the nut moved after I got it on the trailer. There has to be something going on and if I don't correct this the nut will continue to back off the shaft. I have attached a picture of the nut and end of prop shaft showing how much the nut moved after putting the boat back on trailer one time.

IMG_0354.jpg

[avidbasser]

Not sure...but there should be a washer that has arms / braces on it behind the nut. I know my hub has it.

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[dls]

Not sure...but there should be a washer that has arms / braces on it behind the nut. I know my hub has it.
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Mine came with the nylock nut. In wish I had the locking tabs though.

[billnorman1]

Well you better find the cause or it could get real expensive.

[EuropeanAM]

Lock Tabs are not used on the 1.25" diameter Propshaft.

Dls: Which HUB KIT are you utilizing, and what is the propnut being torqued to?

[dls]

Lock Tabs are not used on the 1.25" diameter Propshaft.

Dls: Which HUB KIT are you utilizing, and what is the propnut being torqued to?

The prop nut kit is 840383A2 and I torqued it to 56 ft. lb. The hub kit is the original from the factory. It has 4, maybe 5, rubber sleeves around the outside.

[dls]

Well you better find the cause or it could get real expensive.

Yea I'm trying to but it's like I'm the only one with this problem. I'm hoping Don will tell me something.

[Another Distraction]

The big washer doesn't look concentric with the hub. I see a big space up top like the washer if falling down. Something looks funny.

[mactlman]

The big washer doesn't look concentric with the hub. I see a big space up top like the washer if falling down. Something looks funny.

mine had 2 washers under the nut??

[JohnnyGZ21]

[Pulsare2020]

The prop nut kit is 840383A2 and I torqued it to 56 ft. lb. The hub kit is the original from the factory. It has 4, maybe 5, rubber sleeves around the outside.

I think you should have 3 washers, the large thickest one goes on first, then the thin smaller diameter cupped Belleville washer and then the remaining washer which is a bit thinner than the first one. Mercury as a double nut kit that I believe you torque to 85 ft lbs, that some claim alleviates this issue, but I have no experience with it, and Don once mentioned he has seen prop shaft damage when torqued incorrectly. Mine backs off as well but not nearly as quickly as yours. It takes almost an entire season to move a bit more than yours did in a few minutes. Mine improved when I changed all the washers since I could not purchase only the Belleville washer from Mercury.

[Another Distraction]

Do you have "C" in the correct orientation?hub.jpg
C is Belleville lock washer.

Merc owners manual calls for 55 ft-lbs. My guy at turning point props says 65 for 1.25" shafts.

I have to buy a merc SSRHD hub as I believe you have pictured for my 250 repower so I'm interest in your solution/problem. Keep us posted.

[EuropeanAM]

Most of the newer SSR hub kits contain the double-nut set now (1.25" shaft models).

Proper installation is as Pulseair2020 stated above: Thickest washer (first), thinnest (belleville) washer second, the then the mid-thickness. Install nut, pull down snug and then torque to 55 lbs/ft.

There would be no harm in torquing this to 65 lbs/ft, but even at the spec torque, the nut should not move in the short time span the OP says he was in gear. Shy of an explanation I would suggest trying a completely different hub kit.

[Woody b]

I haven't read anything else about your loosening nut. (I suppose there's a thread somewhere) How loose does it get? I'm an auto tech. I don't always do things "by the book". My first couple thoughts are make it, and re torque it every trip. When you re torque it does the mark like back up or does it tighten further than the mark? If it's just tightening back to the original mark, using the proper torque I'd put some loctite on it.

[kris_tx]

Maybe check torque wrench for accuracy

[dls]

Thanks for everyone's response. The washers are in the right sequence and my torque wrench is checked once a year for accuracy. Every time I have retorque the nut the marks will line back up perfectly. Before this last attempt I did try torquing the nut to 65 ft. lbs. with pretty much the same results. It just so happens that this time my fishing trip was cut short. For all I know the nut may move every time I come out of the hole.

[dls]

Most of the newer SSR hub kits contain the double-nut set now (1.25" shaft models).

Proper installation is as Pulseair2020 stated above: Thickest washer (first), thinnest (belleville) washer second, the then the mid-thickness. Install nut, pull down snug and then torque to 55 lbs/ft.

There would be no harm in torquing this to 65 lbs/ft, but even at the spec torque, the nut should not move in the short time span the OP says he was in gear. Shy of an explanation I would suggest trying a completely different hub kit.

Thanks for everything Don, I will take your advice on replacing the hub kit. What hub kit do you suggest?

[Another Distraction]

Hub part numbers from this forum.
1.25 hub kit_Chrome.jpg

[dls]

Hub part numbers from this forum.
1.25 hub kit_Chrome.jpg

Ok Thanks

[2dwoods]

Have you tried some removable loctite just a thought but seems a new unlock would stay