Mercruiser prop shaft thread size, die to chase threads

[fishrdan]

Hey Guys, what's the correct size of die to chase the threads on a Mercruiser prop shaft, it's a M1 drive, but uses the same prop nut as an Alpha1 or Alpha Gen II. The old prop nut spins on the shaft fine, but the shaft and nut are buggered up a bit, rounded off threads. The new nut from the Flo-Troq hub kit won't spin on the shaft easily as it starts binding on the rounded off threads.

My main concern is torquing the Flo-torq hub kit to 100ftlb with the old worn out nut. I don't want to strip the old nut, or bugger up the shaft by forcing the new nut on the shaft.

Thanks, Dan

 

[Fun Times]

Re: Mercruiser prop nut size, die size to chase threads

Re: Mercruiser prop nut size, die size to chase threads

I looked/Googled this same question up myself one time and found it should be a 3/4-16 thread size on the prop shaft, But I have not checked into seeing if this is the actual size myself yet.

Let me know if you find this size to work because I still need to do this same thing on my personal boat with a bravo 1 drive on the next oil change. Thanks.

Found here.
http://www.offshoreonly.com/forums/general-q/142332-anyone-know-thread-size-pitch-4-bravo.html

 

[Bondo]

Re: Mercruiser prop nut size, die size to chase threads

Re: Mercruiser prop nut size, die size to chase threads

Ayuh,... It is in fact, 3/4" fine thread...

 

[fishrdan]

Re: Mercruiser prop nut size, die size to chase threads

Re: Mercruiser prop nut size, die size to chase threads

Thanks for the quick response!

(I probably could have found the answer easily last year by using search, but search doesn't work well with the new forum software.......)

 

[stonyloam]

Re: Mercruiser prop shaft thread size, die to chase threads

My main concern is torquing the Flo-torq hub kit to 100ftlb with the old worn out nut. I don't want to strip the old nut, or bugger up the shaft by forcing the new nut on the shaft.

That sounded WAY too tight, so I looked it up. They only talked about 100 INCH POUNDS in the instructions (that is like 8 ft lb) for a low horsepower outboard. Alpha 1 should be 55 ft lb. Here are the instructions: http://www.mercurymarine.com/media/mercury/pdfs/service-and-support/props/Flo-Torq.pdf same as all other Alpha I props.

 

[fishrdan]

Re: Mercruiser prop shaft thread size, die to chase threads

The link ^^^ is to the old instructions. Mercury revised the torque setting for the Flo-Torq II from 55ftlb to 100ftlb. The instructions that came with my Flo-Torq II say 100ftlb. I guess 55ftlb wasn't tight enough to completely seat the hub and caused rattling issues, something like that anyway.

I just want to make sure I don't get that sinking felling while I'm torquing the prop nut. You know, then you are torquing something and all of a sudden it gets easier to tighten :facepalm:

 

[stonyloam]

Re: Mercruiser prop shaft thread size, die to chase threads

OK, sorry, the Fow-Torque I is the only one listed on the Merc site, and at twice the current torque 100 seemed kind of high. That is going to be a pain, 55 is hard enough to hold LOL.

 

[fishrdan]

Re: Mercruiser prop shaft thread size, die to chase threads

Success!

The 3/4 - 16 die was a bit tough to work with as I didn't have a handle for the big die, but my trusty ol' crescent wrench facepalm held the die tight enough after snugging it down. 6-7 passes cleaned up the threads and the nut spun on easy, torqued to 100ftlb without issue.