Not quite sure of the best way to tackle this. I've got an external block cavity wall - at least it's external on the top floor, there's a single storey block corridor with pitched tile roof on the ground floor. There are three doorways next to each other in the wall with block columns between them. It looks like a single concrete lintel has been formed in place across all three openings. The lintel's 260mm wide x 180mm high.
I want to widen one of the end openings by around 1200mm, effectively knocking through so the room inside the cavity wall & corridor outside it become one. This means removing the wall that's currently supporting that end of the lintel.
There's not enough space above the lintel to put a new one on top of it (the upstairs floor joists are only about 70mm above it), so the only option I can think of is to cut the lintel at the edge of the last pillar, make that pillar at least 150mm wider with blocks, then fit a new lintel from those blocks across to where the new opening will end.
Are there any other options, & if not, what's the best (cheap) way of cutting through a 260mm x 180mm concrete lintel? I know a hydraulic masonry chainsaw's probably the easiest way, but suspect they're hideously expensive to hire (especially as the few hire sites I've looked at say 'POA' for the price). I have got a 9" angle grinder & diamond disc, but that only cuts to 70mm depth. Start with that then bash away with a cold chisel?