Normal coupler bolts?

[hlev00]

Originally Posted by Dave9111

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

Yes, that is what I am doing. The picture is misleading and I wasn’t clear in my original post. Thanks though.

[Dave9111]

Other options:

Grinder
Grinder with a cutting disk.
Right angle die grinder with a 3 inch cutting disk.
Oscillating tool with a carbide cutter. It will take a while but its very controllable in such a tight space.

A torch. Ive used a propane torch to help with rusted bolts in the same place. You need lots of aluminum foil, etc to shield the fiberglass, etc. It can be scary

[dfelsent]

The gap between my coupler bolts and the transmission was tight. I also wanted to use a torque wrench to properly tighten the fasteners. I used a crow foot socket on the nuts with the torque wrench.
I put the socket at 90 degrees to the wrench to avoid changing the torque reading.
I used Loctite
I rechecked the torque after ten hours (yeah I know dodgy with loctite)
I inspected after a few minutes and a few hours.
Been ok for several hundred now.
It was also a good opportunity to check the alignment.


I peek around the engine every morning when I check the fluids. Coupler bolts. Shift and throttle cables. Look for leaks. General inspection. Takes no time at all.
That’s how I found my loose bolts in the first place.

[betwys1]

Originally Posted by 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

Convincing tests (was it NASA?) have shown that split washers are not very effective. Safety wiring is the gold-standard. This calls for drilled bolt heads.

[skipperpete]

I’m in agreement with Wottie and Betwys about spring washers but putting em under capscrews seems to be fairly common, at least on French built boats with Yanmars, yesterday I was working on boat that had washers on all 4 coupling capscrews as in the OP’s first photo, interested, I went aboard another boat .... similar installation but newer than the first and again, 4 spring washers under the heads of the capscrews. I reckon they do it to avoid the root radius of the coupling flange. It’s a long shot because the head of the capscrews is practically the same diameter as the spring washers which makes it hard to support my theory but there is a bit of lateral movement between the shank of the bolt and the inner diameter of the spring washer so the contact area is moved away from the radius by about .5mm.
A well made coupling and a good alignment should mean that the coupling bolts never come loose so if anyone is having bolts loosening off, a closer look at the alignment might be in order.

[Icarus]

Grade 8.8 hex bolts and flange nuts + high strength threat locker..

[more]

use 12.9 A574 or 10.9 A490/A354BD
and for securing minimum loctite .

ss bolt tensile are usually 500-700 and strongest rare to find Class 80 A4 –80 (316) to soft.
i usually use 12.9 or 10.9 simply strongest easy find on market.

[Wotname]

AFAIK - the torque is mostly transmitted via the friction of the coupler flanges, not the bolts which serve to apply the necessary clamping force.