I realise this is a common question. Almost all of the posts I've read involve using a prop to support the brick structure above before cutting away bricks and installing a lintel, especially if it's a load bearing wall.

However, I really want to avoid the use of an acro prop with needles or strongboy because: a) the concrete floor underneath is strongly sloped (external wall), b) I don't have much overhead room (internal wall), c) it costs money to hire, and d) I have no experience with it. So, I've thought of a way of installing a lintel that doesn't involve supports and can be done with access to only one side of the wall. But, I want to run it by the experienced people here before actually doing it!

My specific situation:
External load bearing double-brick wall with cavity. The internal wall is supporting floor joists and the external wall is supporting the roof. The opening is at the basement level with single level above. Lime mortar.

The plan:
Grind out the mortar in horizontal sections of 150 mm at 100 mm deep (only leaving 10 mm of mortar under the other face of the brick), then insert a 150 mm long piece of 16 x 8 mm flat bar under and near the face of the brick. (The flat bar supports the brick on the side where the mortar has been removed.) Keep doing this for the full span of the lintel. Then push back every third flat bar to pump mortar into the entire joint. Then push in a 150 x 90 x 8 mm angle lintel (so 82 mm (90 - 8 mm) goes under the brick). The mortar can't escape via the other end because of the 10 mm mortar left in place, the flat bar gets embedded in the new mortar between the original mortar and lintel. At no time in the process are the bricks left unsupported. Once the lintel is in place and the mortar set, cut out the opening below.

Will it work?

Read and reply to the full thread at RenovateForum.com....