I’ve got a drive belt fitted in a way that it stays on the pulleys when turning the engine by hand and with the engine running.
I will post a photo when home from the allotment.
I’ve had to fit a loose belt to be able to start the engine. I couldn’t turn it over fast enough with a tight belt.
I’ve had the mower blade spinning by tensioning the drive belt by with the edge of a spanner with the engine already running.
Just got to figure out a way of tensioning the belt for normal use.