Propeller nut - mercruiser

Rnichols2

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I had a brass propeller nut that threads stripped out. I got a replacement but it was extremely hard to go on, so not wanting to strip threads on shaft I stopped. I have a 1979 mercruiser 140 hp. The New prop nut is the same size as the old one so is it possible there are different threads on this older prop shaft?shaft?
 

alldodge

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Howdy

Is it a .750 x 16 thread?
Or maybe better yet, what is the part number?
 

Bondo

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I have a 1979 mercruiser 140 hp. The New prop nut is the same size as the old one so is it possible there are different threads on this older prop shaft?shaft?

Ayuh,.... Welcome Aboard,.... It Should be the same,....

Did ya check the threads on the prop shaft for damage,..??
 

fishrdan

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Check the prop shaft threads as Bondo said, 40 years of use and a stripped nut probably buggered up the threads.

I didn't have a stripped nut, but when I put a new nut on my ol' 72, it was way too tight for comfort. I chased the prop shaft threads with a die and it was good as new. Make sure to get the die started straight, use lots of oil, go slow and don't try to cut the whole shaft in 1 shot. I don't remember what size the die was, but picked it up at the local "good" (Carquest/NAPA) auto parts store, $15 or so.
 

Rnichols2

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dont know the part number of the new nut I have,it was given to me by the shop that is repairing the stainless prop, however, I did a cross reference on the part listed in the parts manual, it is 11-52707 which cross referenced to a Siera 18-3700, so I ordered one on line.. It is a 3/4 nut, but not sure about the number of threads, I saw one listing that said that nut was !6, and another said it was 20. I considered getting a 3/4 - 16 die, but wanted to make sure the prop shaft was 16, which I Think is considered "fine". I didnt want to put the die on the wrong threads, thats why I was wondering if Mercury used different threads. The prop nut went on maybe 4 or 5 turns, but it was hard so I stopped. This prop hasnt been off in quite a while. I still have the original aluminum prop, but have had a stainless steel on it for the past 35 years, which brings up another question, I have two Front thrust washer, part #12-835467-5, and 77897. The 77897 is about 1/4 inch thicker. everything with the original 12-835467-5, but I have been told it was too thin. The prop has a 1/2 inch lip and on the end that goes into the housing. It goes in about 1/4 inch leaving 1/4 inch.I might add, that while this boat is 38 years old, it only has 390 hours on it, so obviously it doesnt run a lot. This all started when I hit something under water and I had a mechanic replace drive shaft, lower shift cable and other things just because of age. By the way,from an appearance standpoint, the threads on the prop shaft appear to be ok. . So should I assume that everything has been working to just put it back like it was when I get the stainless prop back?
 

Rnichols2

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Thats all assuming I can get the threads on the shaft so I can put the prop nut on. The splines are also blunted on the ends so it appears I will be taking a file on the end of the splines so the prop can slide on without me banging it with my fist and busting kinuckels.
 

Rnichols2

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thanks, i counted threads and there 16 in an inch. I kinda botched the prop change. The stainless steel came off with some difficulty but did come off, so I took it to repair shop to repair dings. Tried to put original aluminum prop on and couldnt get it on splines, guess i burred the ends on some of the splines. Is it ok to take a rat file to smooth our the ends of the splines. Must have had a senior moment, Ive changed props before and never had a problem. I will be getting a die to clean up the threads on the shaft.
 

alldodge

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Your not going to hurt it with a file, its hardened steel
 

fishrdan

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Wrap the threads with tape to protect them, then have at the splines with a file.
 

Rnichols2

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Thanks for all the good advice. I will get stainless prop back in a couple weeks and tear into it
 
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