Stone lintel fireplace crack

[Jumble]

Hi,
I've just uncovered the third fireplace in my 1860s terrace. The first two I uncovered are lovely stone fireplaces, all straightforward and easy to clear out and fix up, with nice even slabs of York stone as their lintels.
The third one is unlike any lintel I've ever seen as it's got the wonkiest stone lintel going and I love it and really want to keep it. The only problem is that it's got a crack right in the middle and I need advice on how to strengthen it or whether or it's okay as it is. The entire fireplace is solid and none of the bricks or stones are moving. I'll be repointing it in lime mortar. I'm going to get acro props tomorrow to shore it up before removing the cement arch addition that was put in by a previous owner for a gas fire.

Any advice would be appreciated, thank you!

 

[tell80]

Please post a pic after removing all the rubble and chattels, and the "cement arch addition" surrounding the opening?
Perhaps a steel supporting bar can be used as a kind of lintel for the stone lintel?

Is the gas restrictor still visible - or any gas pipes or elec cables?
The fireplace back will need wire brushing clean and the flue sweeping - have the other two fireplace flues been swept?
The hearth will have been constructed on soil and rubble - the joists trimming the hearth might be rotting - can you crawl the floor & examine them?
The RH corner bead is a skim bead, if you replace it then use an Angle Bead.

 

[Nige F]

Yeah get your chattels out

 

[Jumble]

Thanks so much for all your advice, tell80! I forgot to say that we're three storeys up so luckily all beams are dry and the hearth is a slab of Yorkshire stone.
We've been in touch with a fireplace builder and they've said that the stone, although cracked, is very secure.
The gas supply has been cut off many months ago, just haven't been through the floorboards to remove the pipes yet.
I can't wait to get started on this one, now I know it's safe!

Thanks again,
Ju

 

[mrrusty]

As the risk is only ever the triangle of bricks over an opening - the rest of the forces get corbelled outwards, that is going nowhere, crack or no crack. The two sides are propped against each other.