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After soaking the set screws on my starboard side prop shaft coupling for nearly six months, I tried to loosen them with a four point socket and a breaker bar. The first one came right out but the second one broke off flush with the coupling.

I have a four inch angle grinder and a box of cutting disks. Is this the appropriate tool to cut off the coupling?

I found some instructions on line which said to make cut the length on the coupling in line with the slot for the key so you won’t damage the shaft. They said to make s second shallow cut on the opposite side so that you can pry the two sides apart. Does this make sense?

Given that I will be working near the gas tank is there any danger from the sparks the cutter will throw off?

I think I would try first with some left handed drill bits (https://www.grainger.com/category/machi ... ters=attrs) on the remaining set screw. I don't like grinding and look for the solution that has me removing the least metal possible.
If you get lucky the heat and grab of the drill bit may back the set screw out. If not, I do not think this is an application where you were worried about saving the coupling - to my way of thinking that increases your chances of getting a pilot hole dead on.
Good news is all that soaking got you the first one and will likely help when it is time to slide the coupler off.
Good luck.
Stephan

Is there anyway you can drill the out the bolt? To me that would be the safer bet. I assume you planned on putting in new couplings anyway.

Another thought, is there any threads exposed on the opposite side. If there are, maybe you can put a bolt on it and tighten it to lock it in place against the nut against the coupling. Then try and get a wrench on the inner nut and see if you screw it out that way.

I will try to drill it out but I am not optimistic about it as I understand that the set screws are hardened steel.

The screw broke of flush with the surface so no threads are exposed.

If you have access to a welding set up or a welding guy, I have seen my machine shop guy tack weld a nut to the broken off bolt. Then with heat and a wrench he was able to back out the bolts from my transmission flange.

They always break off flush.

The bolts are case hardened, the outside is hard with a soft core. Its why they feel deceptively strong when cranking on them.

Left hand drill can work. Cobolt grade drills are a good choice if you can get them.
When drilling keep speed of drill down avoiding straw colored chips...Straw color is an indication of the drill bit getting too hot and will soon lose its hardness. Blue chips are way too hot...

If you decide to use a grinding wheel to cut off...they can be very dangerous if the wheel shatters or kicks back/gets stuck/pulls from your hand. Protective eyewear is a must, face shield not a bad idea. Gloves...your call, thin don't give much protection and thick offer more protection but for me it comes at a price of losing some feeling and grip. A wheel spinning that fast goes through skin like its not there.

The sparks/swarf...it comes off hot. It can melt plastic and rubber, burn through paper and cloth. It can ignite flammables and combust combustibles if directed to a point for long durations. How long...I can't answer as it depends on how close to the cutting area, how hot the swarf is...how dry and flammable the______is. Don't direct to your tank, fule lines etc. If you don't have a choice...a welders blanket or similar works well.

Flanges are usually cast iron and swarf comes off as a powder...that stuff gets everywhere and makes a mess...then it rusts and makes a bigger mess.

Sometimes if you can get a sawzall in...slice off a piece of the flange so you don't need to cut so deep with the grinding wheel.

I found a chain vice grip wrench really useful for this job. I put an old leather work glove between the chain and the shaft and then let the back of the wrench jam against the hull or the stringer. It kept the shaft from wriggling around while I swore at it.

Use a Dremel with a carbide burr to get the broken off part flush if needed. Center punch and use a left had drill on it. Go a little undersize and try to stay out of the threads if you are going to reuse the coupling.

...and if you do go into the threads...not the end of the world to go up a thread size.

Carl wrote:...and if you do go into the threads...not the end of the world to go up a thread size.

I’m going to be putting new split couplings on both sides so I am not worried about the threads.

were is the boat located on Long Island?

Bob,

She is at Westin’s in Sayville.

ok i will check it out Monday May 18 around noon time .

Bob

Thanks.

I will be there Monday morning until around noon. I am going to try drilling the set screw out with a cobalt bit.

Carl,

I followed your directions and used a 5/16" cobalt bit, running the drill at slow speed. It took me about two hours, not including breaks to rest my arm, to drill out the set screw. My hole was a bit more than 1/16" off center so there was a fragment of a bolt left in the forward side of the hole. I was able to exact the top 3/8" of that with a hammer and a nail set. I could see from the fragment that came out the my hole had gone straight.

I worked on it a bit today with a flange puller but ran out of time. Meanwhile, I have it soaking in Corrosion-X which I hope will loosen it.

i went to Westin the only 31 Bertram i saw was the one with the green glass windshield and that is in the water! are you doing the shaft log repair while the boat is in the water?

Bob

I am in the lot across the street, behind the freight company warehouse. If you pull into the lot you can’t miss her.

I just sent you a PM with my cell phone #.

pschauss wrote:Carl,

I followed your directions and used a 5/16" cobalt bit, running the drill at slow speed. It took me about two hours, not including breaks to rest my arm, to drill out the set screw. My hole was a bit more than 1/16" off center so there was a fragment of a bolt left in the forward side of the hole. I was able to exact the top 3/8" of that with a hammer and a nail set. I could see from the fragment that came out the my hole had gone straight.

I worked on it a bit today with a flange puller but ran out of time. Meanwhile, I have it soaking in Corrosion-X which I hope will loosen it.

2 hours...that is dedication right there!

Not being able to see what it looks like I'll leave to you to decide if the set screw could still be holding the shaft in place. If you think it is, then going up a couple drill sizes should remove what is left of the broken bolt. The cast iron flange drills like butter and one your down to the set screw...having the hole in it already makes drilling it a snap...till the broken set screw comes loose and mucks things up. But at that point its usually dislodged enough to come right out.

A carbide burr or ball mill in a Dremel also works to grind/cutaway the set screw...if your handy with them. That is the way I had to remove a broken drill out of a broken stud is a buds turbo over the winter. Would have been so much easier if he just let me remove the broken stud for him...but he had lots of help with Idea's. Can't say no to ideas...

Carl wrote:...A carbide burr or ball mill in a Dremel also works to grind/cutaway the set screw...if your handy with them...

This.
I never seem to get my pilot hole just right and am left with an off-center hole that is touching the threads on one side and part of the stud/bolt on the other. I have had good luck with the Dremel burrs but have to run them slower to avoid heating them up too much and loosing the abrasive. I buy 2 more than I think I'll need.
I have had luck using the burr to cut a trench down the middle of the remaining bolt and then using a punch to sort of fold the two halve of the bolt in, away from the threads and then plucking it out with a pick.

Finally got it off.

I saturated it with CorrosionX for a week or so. Then I used a Buck-Algonquin puller. Instead of using the center screw which has a coarse thread, I used four 3” fine thread bolts. I tightened the center post enough so that there was a half inch gap between the flange on the puller and the coupling. Then I tightened each bolt a quarter of a turn at a time until they wouldn’t turn. I then hit the flange two or three times with a hammer 180 degrees apart, then continued tightening the bolts. I had to reposition the puller three or four times.

The whole process took about two and a half hours.

Thanks to everyone on the forum here for all of the encouragement and suggestions.

Now try to explain that to an irate customer who wants to know why his mechanic charged $100 to change a coupling.
Loosen a few screws take off, put the other one on...how long can that take.

Some of my friends/customers were the boat mechanics...so when I'd get an ear full I'd try to explain. Few got it, others didn't till they tried to do a seemingly simple job that they thought the quote was way overpriced. Some of them just climbing down in the whole had the tune change to worth every penny.


Glad you finally got it off! They can be a royal pain

Carl wrote:Now try to explain that to an irate customer who wants to know why his mechanic charged $100 to change a coupling.
Loosen a few screws take off, put the other one on...how long can that take.

Exactly. I figure that the whole task took me at least eight hours, not including a few false starts.