Normal coupler bolts?

[Bellinghamster]

If it comes to grinding it off, either confirm there is sufficient clearance between the transmissions coupling and transmission housing to remove the remaining stub and nut (forward) or grind through the nut so you can remove it (aft) where you have plenty of room.

[MicHughV]

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

Quite correct, I do this now

[FPNC]

Apply heat with an oxy/acet torch to the nut. Fine tip. The bolt looks like a 12.9 class metric. Which is very hard and strong. However it is not impossible to strip out the drive end.

[hlev00]

Originally Posted by Bellinghamster

If it comes to grinding it off, either confirm there is sufficient clearance between the transmissions coupling and transmission housing to remove the remaining stub and nut (forward) or grind through the nut so you can remove it (aft) where you have plenty of room.

Thanks, that occurred to me too. There won't be room to extract forward so no grinding from the aft side. I am hopeful that a 6-point, ground down slightly, will fit. My 12-point almost fits as is, but not quite, so I shouldn't have to take too much off.

[Wotname]

Another note -

After a closer look at the picture, it appears there are no threads protruding past the end of the Nylok nut. There should must be 2+ threads visible to ensure the Nylok is working as designed. Any less and the security of the nut is compromised. The addition of the split washers under the bolt head has shortened the effective length of the bolt (poor practice).

So there are three issues to avoid when refitting.
1. Spilt washers are to be avoided.
2. Thread protrusion should be 2+ threads
3. For best practice, Nyloks should not be reused but in non critical circumstances, some will reuse them once or twice.

[skipperpete]

Wottie, the last line of the post was very astute, lacking a small diameter hard steel washer for a job that needs one I often take the twist outta spring washers with a vice and an adjustable spanner and thanks to the poster for reminding me that “Unbrako” was once the generic term for capscrews…. And the hex keys that fitted em. Yes, the unbrako’s were grade 8 and aptly named. The tendency to use allthreads in couplings is a bad thing, a bolt with a properly chosen grip length is the “according to Hoyle” correct method. Heavy duty ship couplings not only have the shank of the bolts to the correct length but they are also a drive fit into reamed holes and individually numbered.

[Toccata]

I would grind the head off (from the aft side), with a wet towel placed around the area.
Tap the bolt forward as far as possible, then grind the forward side of the bolt, behind the nut.
Possibly easier to grind through the bolt than the nut? although sometimes if you grind through the nut you can get lucky and the nut will fall off (with persuasion) then "Bobs your uncle"
Good luck.

[Emmalina]

This got a bit clunky !

[hlev00]

More to chew on...

On another site where I posed the same general question as this thread, the discussion of what type of bolts should be used came up. Then general consensus was Grade 8 or 10.9 for metric and generally yellow zinc chromate finish. One individual suggested that he preferred a cadmium finish for better corrosion resistance. Several sites sell coupler bolt sets in Grade 8 with the yellow zinc chromate finish so that at least seems to be a common solution. They also sell them with split washers. That topic was addressed earlier but they seem to still be popular.

One other person chimed in suggesting that Grade 5 was superior as it gave some hope of the bolts sheering off before damaging the shaft et al in the event of wrapping a line around the prop and shaft. A little additional searching came up with a few others suggesting this or even lower grade steel for protective purposes. Or the Driversaver Flexible Coupling.

[Wotname]

Personally I would not rely on weak bolts as a protective mechanism. It is far too arbitrary for me; too hit and miss. I would put in 'proper' sized bolts. If I was looking prop protection, I would want a commercially engineered solution.

Regarding the split washers, they are included because everyone expects to see them. We have being seeing them for a century or more so they 'must' work - except they don't...

NASA (and others) have not got this wrong. You won't find them on that rescue helicopter that drags you back to shore after your boat sinks from a failed shaft coupling bolts!!! Aerospace guys are vibration conscious and they use proper proven methods to control fastener security.

It probably doesn't hurt to fit the spilt washers providing you add some real security (Loctite or Nord-Lock washers etc) but I have never used them after I learning better!

[Stu Jackson]

Originally Posted by Wotname

Personally I would not rely on weak bolts as a protective mechanism. It is far too arbitrary for me; too hit and miss. I would put in 'proper' sized bolts. If I was looking prop protection, I would want a commercially engineered solution.
>>>>>>>>>>>>

I was under the impression that if one got a wrap of some line around the prop or shaft, the engine would stop.


Mine did.

[Shaneesprit]

Originally Posted by 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


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

I didn’t read your post but my first thought was what the hell are split washers doing there. Inappropriate use.
Replace with flat washers, new nyloc nuts and the bolts, well as long as they are high tensile and the same diameter & lengh. To be honest the Nyloc might even be overkill. .

[hlev00]

Originally Posted by Shaneesprit

I didn’t read your post but my first thought was what the hell are split washers doing there. Inappropriate use.
Replace with flat washers, new nyloc nuts and the bolts, well as long as they are high tensile and the same diameter & lengh. To be honest the Nyloc might even be overkill. .

Yeah, the split washer location is the work of a previous mechanic. My guess is that Nylocs were chosen as it is pretty hard to get an open ended torque wrench into the little gap between the heads and gearbox.

[vpbarkley]

The use of socket head cap screws with Nylock jam nuts looks perfect to me.

Those socket head cap screws are 20% stronger than grade 8 hex bolts.

I would use anti-seize compound when you reinstall them for ease of removal.

[Dave9111]

You are trying to turn the wrong part. Turn the nut, and hold the allen head capscrew.