Neil: please share something with a photo? I am lost at your mention of a "second" electric starter motor. I thought of a "shotshell" starter once, and would do it if it could be adapted to a pony motor.
Dual starting option has been welcomed here. I saw someone once have a starter rigged up to their D6 because the pony was dead, and they left it in place; I was not the first most likely, but having the properly functioning pony engine and a direct electric 12V starting system sure makes life much more pleasant. The pulling of the rope gets old at times, even if the pony starts on the first or second attempt. Perhaps I am getting lazier in old age.
The D2s, D4s and D6s here set up as dual start cost some coin, and not original, but when there is usually only myself to start and move things around, it speeds things up. I swear I can never keep enough gasoline on hand, and the pre start procedure takes up a lot of time.
There have been times where someone has accidentally killed a motor, and a quick re-start is in order!
Like some folks tell me, work smarter, not harder? JM

My goodness Neil. Another way to start a tractor hahaha. I have never seen these before. Interesting concept for sure.
Feel free to do one of yours up with the "spring starter" and let us know how you liked it. Those would be kind of neat to try on a pony. Battery poor here. The rope pony D2s that run good here won't get swapped to electric in any manner. JM

Hi, Folks.
The German manufacturers, Klockner-Humboldt and Deutz, seemed to like 'clockwork' starters. Another German manufacturer, Maybach, seemed to like inertia starters.

'Sproing' starter fitting and operation:





GOTTA LOVE this kid:



Maybach Inertia stater:



Food for thought???????????????????

Just my 0.02.

Tiger is not a (Spring Starter) Schwungmasse.

Hi, restore49.
Well, I suggest that you go tell that to the person who posted that video. And did you read the blurb below the video, the bit where it said that the INERTIA starter was the preferred method of starting in cold weather due to batteries being less reliable in those days but that the unit DID have electric starting?????????????????

Just my 0.02.

The Tiger tank is an inertia starter. That is the only one that gives me shivers up and down my spine!

Hi, hfdzl.
The tiger had electric starting but it also had the inertia starter for use in cold weather 'coz batteries were not as reliable back during WW2.

Just my 0.02.