Normal coupler bolts?

[hlev00]

The bolts for my Beneteau/Yanmar shaft coupler are hex sockets. On the aft side of the coupler the machine screws are inserted through split washers then through the coupler. On the forward side nylock nuts are used without any washers. Seems like an odd arrangement. The machine screws themselves are black. Most pictures I have seen are hex bolts with a nut and split washer on the front side. I have managed to free all but one, naturally. I am afraid of rounding out the hex socket. I am trying some PB blaster and will attempt again tomorrow.

My question is mostly though whether I should put these back or replace with something else.

Thanks,
Harry

[skipperpete]

Hi there Harry, try locking up the coupling and pitting all your energy into undoing the Nyloc nut with a good quality open end wrench rather than trying to turn the cap-screw.... if it goes badly and the nut rounds off just split it with a chisel and hammer, you’ll probably find that the first couple of well placed chisel hits will loosen the nut and you may be able to resume with the open ender. If you decide to use hex head bolts you may need to grind part of one flat of the hex to clear the radius and hub on the shaft coupling, perhaps use those spring washers again.

[michaeld]

I recommend grade 8 bolts and nuts with split washers. Lube them up good for the future. Better yet, contact the tranny manufacturer. Get their specs. You don't want those bolts to shear off. Ask me how I know.

[Wotname]

Spilt washers are the work of the devil. They meant to prevent a fastener from loosening as a result of vibration. To work, they should lie directly against the nut, must not be over tensioned and never tensioned enough to be squashed flat. 99.9% of the time, they are decorative at the best and at the worst, they give a false sense of security and can be worse than no washer. There are many better ways of keeping the fastener secure against vibration - chemical thread locking (Loctite), Nyloc nuts, tab washers, lock wire, paired nordlock washers etc etc.

NASA states in publication 1228 https://ntrs.nasa.gov/api/citations/...9900009424.pdf

The typical helical spring washer shown in figure 14 is made of slightly trapezoidal wire formed into a helix of one coil so that the free height is approximately twice the thickness of the washer cross section. They are usually made of hardened carbon steel, but they are also available in aluminum, silicon, brome, phosphor-bronze, stainless steel, and K-Monel.
The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking.

Also many other sources
https://www.boltscience.com/pages/he...ingwashers.htm
https://www.bolts.co.uk/guides-and-t...n-to-use-them/

[Jim Cate]

^^^^
Wottie, you again amaze me with your knowledge! And it makes me cringe at the years that I've depended upon these damn things to work. Next thing you'll be telling me there ain't no Santa Claus!

Jim

[MicHughV]

As an addendum to above recommendations to prevent those bolts from unscrewing,
you could :
1. place a small hose clamp around the bolt head and tighten this so the arm of the hose clamp sticking out bears against the coupler preventing the bolt from turning.
2. as above, drill a small hole thru' each bolt head and run small dia. s/s wire thru' all four bolt heads to prevent movement.

I've now, not once, but twice, had coupler bolts come loose and fall off due to vibration and am somewhat paranoid of having this happen a third time.

I've resorted to both examples cited above on different boats, and have not had a problem afterwards.
Though every time I stick my head into the engine compartment, my roving eye always gives the coupler a looksee to see that all is well there.

[hlev00]

Thanks for the suggestions. I am still reading them over but I realize I was not clear and the picture did not help. I am using the hex socket side to prevent the shaft from turning, while trying to back off the nylok with an open end wrench opposite. I really wish I could get the closed end around the nut. Maybe my wrench isn't as good / accurate size as I need.

Thanks again. I will report back.

[Emmalina]

Looks like nylock nuts so why have a split washer ?

[skipperpete]

Originally Posted by hlev00

Thanks for the suggestions. I am still reading them over but I realize I was not clear and the picture did not help. I am using the hex socket side to prevent the shaft from turning, while trying to back off the nylok with an open end wrench opposite. I really wish I could get the closed end around the nut. Maybe my wrench isn't as good / accurate size as I need.

Thanks again. I will report back.

Often you can get a ring spanner onto the nut, you just have to grind it and bend it till it fits through the gap. I have a selection of bent, welded and ground down spanners for just such an occasion, Allen keys too......they’re an ugly little group but are worth their weight in gold.

[MicHughV]

While I'm at it, another past failure issue was the retaining bolt holding the shaft inside the couple, this too went missing in action one day. Another hose clamp to the rescue.

I was waiting at a bridge to open, and had put the engine in reverse for a second, but no reverse motion was to be seen. I rushed below to see a 1" diameter stream of water pouring into the boat thru' the shaft stuffing box, where the shaft should have been, as the shaft had simple rotated backwards with nothing to hold it in.

To say this was an unnerving sight would be an understatement.

I immediately jumped overboard, and lady luck, as usual, was sitting on my shoulder, as the prop shaft was still dangling on the rear cutlass bearing support, which I managed to shove back in with my last gasp of air.

In the interim, the wind had blown me out of the channel and I was aground on a falling tide, this allowed to me to address the problem, and ponder my plight for the next 6 hours, while I soothed my nerves with a beverage or two...or was that three or four....

Anyway, I relate this tale only to impart the dire consequences that could happen, if the above identified bolts vibrate loose.

[pbiJim]

I often place washers under the heads of bolts that I expect I will some day need to grind off or cut off with a torch. This prevents damage to the underlying surface when the cutting takes place.

Socket Head Cap Screws (Allen bolts) come in many different grades. Most of the off shore stuff is low grade, including Holochrome World. American made black alloy SHCS from companies like Holichrome (the owners of the brand name Allen) and Camcar/Textron are high end & very strong. There is only one brand that beats them & that is Unbreako. Look up the specs for yourself & compare them against grade 8. The numbers don't lie.

Start with a good quality Allen Wrench that is not already a little rounded in the corners. If it is a little rounded, grind it back to a fresh surface before using it. If you can find a production grade Allen socket that goes on ratchet, that is best by a long shot. The difference in rounding torque is more than double that of a common good brand Allen Wrench. Unfortunately they are very expensive & hard to find. Industrial suppliers sometimes have them. The stuff from Snap On is not even close in quality. Expect to pay around $50 for a single production grade Allen socket.

If you do slip the Allen wrench in the screw head, then grab the outside of the head with vice grips. If you want to make that work even better, file a flat on one side first. The only thing better than that is welding an oversized nut on the rounded Allen head.

If that fails, grind off the head. The washer under it will prevent damage to the flange. If you had good long access to the end of the Allen screw, I would suggest drilling off the head, but it looks like you don't have that kind of access, so a small grinder would be the weapon of choice from my arsenal.

[Bowdrie]

One doesn't need to go thru a lot of trouble or drama to get high strength bolts.
The "ARP" company makes super-strength bolts with a variety of heads.
Also special nuts/washers.
Most any decent auto shop can help you with the products, or a phone call gets quick results.
Much of what is in the catalog will not be for shaft/prop couplings, but within ~180 pages you might find something to work.
https://arpcatalog.com/

[deblen]

Originally Posted by MicHughV

While I'm at it, another past failure issue was the retaining bolt holding the shaft inside the couple, this too went missing in action one day. Another hose clamp to the rescue.

I was waiting at a bridge to open, and had put the engine in reverse for a second, but no reverse motion was to be seen. I rushed below to see a 1" diameter stream of water pouring into the boat thru' the shaft stuffing box, where the shaft should have been, as the shaft had simple rotated backwards with nothing to hold it in.

To say this was an unnerving sight would be an understatement.

I immediately jumped overboard, and lady luck, as usual, was sitting on my shoulder, as the prop shaft was still dangling on the rear cutlass bearing support, which I managed to shove back in with my last gasp of air.

In the interim, the wind had blown me out of the channel and I was aground on a falling tide, this allowed to me to address the problem, and ponder my plight for the next 6 hours, while I soothed my nerves with a beverage or two...or was that three or four....

Anyway, I relate this tale only to impart the dire consequences that could happen, if the above identified bolts vibrate loose.

Suggest you install a split donut zinc anode on shaft ahead of stuffing/packing,to prevent loss of shaft./Len

[hlev00]

Originally Posted by skipperpete

Often you can get a ring spanner onto the nut, you just have to grind it and bend it till it fits through the gap. I have a selection of bent, welded and ground down spanners for just such an occasion, Allen keys too......they’re an ugly little group but are worth their weight in gold.

I was trying to imagine something like this. The closed end almost makes it through the gap of the gearbox and the nylok head. I hadn't gotten to the "grind a little off" stage in my thinking. Might never have.

I would feel even better with a 6-point combination.

Thanks!

[Wotname]

^^ that is exactly what you need - a 6 point ring the exact size and an angle grinder.