Best way to remove these fixings on mastheaf?

[steve yates]

Mastis down and I need to replace the sheaves and the rigging.

There is a bracket at the top fixed with a ss allen style bolt. (1 in the pic) A size 4 allen key fits but its just not gripping and carving out the hexagoonal shape in the head. 4.5 is too big to fit.
Is drilling it out my only option? Cobalt tipped bits?

The sheaves are fixed by god knows what, looks like flattened metal, rivet style. (2 in the pic)
I’m assuming I will need to grind that off?

 

[B27]

The allen screw may be imperial.
A bodger's trick is to hammer in a Torx bit.
Otherwise, drill it out. A left-hand drill bit is sometimes good, it will grab the screw and undo it, if you are lucky.

The rivetted-over sheave spindles, I would probably attempt to drill to remove some metal below the surface of the alloy, rather than just grind flush, because the holes in the alloy may be countersunk a little.
The RH one looks quite close to the edge of the alloy if it'd heavily loaded?

 

[Clancy Moped]

Worth a shot.

 

[steve yates]

The allen screw may be imperial.
A bodger's trick is to hammer in a Torx bit.
Otherwise, drill it out. A left-hand drill bit is sometimes good, it will grab the screw and undo it, if you are lucky.

The rivetted-over sheave spindles, I would probably attempt to drill to remove some metal below the surface of the alloy, rather than just grind flush, because the holes in the alloy may be countersunk a little.
The RH one looks quite close to the edge of the alloy if it'd heavily loaded?

I tried the imperial keys, toolarge or too small.

 

[wrr]

Drilling out stainless with a handheld drill on a mast that may move under pressure is no fun. I would remove the headbox from the mast. This would allow you to centrepunch and use a drill press to sort out the various fastenings in your or somebody's workshop. You can then properly replace the sheave spindles etc. The headbox can then go back with appropriate anointing with Duralac or Tef-Gel. Good luck!

 

[rogerthebodger]

I would take an angle grinder and grind the heads off and drift the remaining bolt out the other side

 

[B27]

Drilling out stainless with a handheld drill on a mast that may move under pressure is no fun. I would remove the headbox from the mast. This would allow you to centrepunch and use a drill press to sort out the various fastenings in your or somebody's workshop. You can then properly replace the sheave spindles etc. The headbox can then go back with appropriate anointing with Duralac or Tef-Gel. Good luck!

To do that, you have to drill out 3 rivets by the look of it?

I find a good way to start the drill is to grind a dimple with a diamond or carbide burr in the Dremel.
Handy when you can't easily use a hammer and centre punch, or your centrepunch mark is mysteriously off-centre.
If needs be, you can Dremel the peened-over shaft until it taps out easily.

 

[steve yates]

Ideally I’d like to do this without removing the masthead, if I can.
I’m leaning towards the angle grinder at the moment, though dubious about that and drifting out the bolt with the mast just balancing on two trestles.

 

[fredrussell]

I would take an angle grinder and grind the heads off and drift the remaining bolt out the other side

Same here. Position a stout piece of wood between the ground and the mast head before drifting out the remnants of bolt.