With some tweaking and adjusting the machine, it now types again! Several surprises in the adjusting (and it's not done yet). The hardest part to get right so far, was the line gauge. The new rubber platen is very grippy. So much so that the slightest touching of the line gauge to the platen blocks the carriage advancing.
Another adjustment to be done was the carriage bearing rail. Worried about the sprocket leaving its track and any play, I'd initially over-tensioned the carriage. Given the four screws that hold the rail a turn to loosen and gently letting the rail move out a bit. That way a close fit without putting any pressure on the bearings was found. Another thing is that this is really best done without the outer frame fitted.
This outer frame blocks easy access to some screws. Best put on as a last step. Another tricky one is the crossbar that holds the rear bottom screws of the outer frame. This crossbar must be put in place before sliding the outer frame in place - there is no way to get it in afterwards. The tensioning nut on one end of the crossbar can be used to wedge it in place. Getting the tension on this nut wrong will block the shift, by the way. If the inner frame is pinched or pried open there, the shift levers are pinched and it won't settle back to lower case.
Next to the reference machine, the patents on the Remington Portable typewriter are also a neat source of information. These show the construction itself as well as some of the reasons-why behind the construction.
The actual tension on the carriage motor spring is a bit less critical. Just enough tension to accelerate the mass of the carriage at the very end of the line. With the adjustments removing all the little snags and frictions on the carriage, the spring can be released until the least tension that still works is found.
As a last step, the spacebar limiter bracket (part 76 with pads 77 in the figure) was fitted again. After fitting this little bracket, nothing worked anymore.
That was a bit surprising actually. When typing the carriage no longer moved, piling all letters on top of each other. Poking and prying around a bit, the cause was found in that the bracket kept the spacebar down a bit too low. When the spacebar is not let back up far enough, the lever that releases the escapement is not fully releasing the escapement mechanism. Then the escapement is stuck 'half-way' and nothing indexes anymore. Some careful bending and/or new pads (part 77) fixes that.
Still to be tweaked is the position of lowercase and uppercase against the platen, but it does now type again.
The new soft platen is a mixed result so far. On the plus side the grip on paper is solid and the sound a bit less harsh than a hard platen. On the down side the rubber is so soft that the imprint of the characters gets a bit smudged when striking a bit too hard. Overall it makes the machine very sensitive to the typing itself in quality of printing.
Maybe to take off again and replace with something more firm (and reduce the diameter of the right hand side a bit more).
Starting to look better (and type better :)