The 1931 101 has a fixed (correct me if i am wrong) rear drum+ sprocket and the highest option 22T front sprocket. 43/22=1.95

The previous years 45" scouts have for solo duty 21-36 36/21=1.714 or 21-40 .

40/21=1.90 for heavy duty

It seems the gearing of the 1931 is too short and it is capable in my opinion for cruising at 85-90 kph (50-55mph) with less stress on the engine and maybe less vibration. 

I currently have 22-43 and thinking of putting a 23 front (option for the Chief but not for the scout). From the drawings it will be 4.5 mm in diameter larger than the 22T, has anybody done this before? as i see my bike it will fit marginally in the chain guard of the bike.

43/23=1.87 so in theory it will be similar to options from other years and will not be a problem in uphills while better in cruising.

Hello Konstantinos , There is only one way to find out what it's like ! GO for it and let us know how you get on ! Good luck , Ken

Finally got the 23T sprocket. It is a very tight fit but can be done. I thought it would touch the upper side of the chain cover but the problem is mostly the lower side  (on my bike). Anyway with a bit o fiddling it can be fit, i believe it is worth it, not ridden yet.

Hello, yes i had no problem at all.

Tim,  Interesting thought that the late 101 had the primary helical gear ratio changed near the end of 31.  I find that pretty hard to believe, because they knew the 101 was doomed after 31 because of cost of manufacturing 3 different bikes in a terrible depression era market.

  The big culprit in the low gear ratio for 31 was the introduction of the new internal expanding rear brake. This was fitted to all models in 31, Scout, Chief and 4. Other than the rim size, spokes and sprocket alignment on the drum, the entire wheel would interchange between models.  The internal expanding brake was a huge upgrade from the external strap design introduced in 26.  The trade off was the size of the drum required a larger sprocket, 43 teeth being the minimum, resulting in an overall lower gear ratio. The 4 was able to accommodate a larger transmission sprocket under the chain guard so the high solo gear ratio could be raised easily enough.  The Scout and Chief were not able to handle a large enough sprocket under the chain guard to maintain the high solo gear ratios from previous years.  The Chief did receive a new primary drive gear ratio in 31. This required new inner and outer case castings, with the idler shaft relocated and new engine and idler gears.  These new cases will not fit the Scout. This was a fair amount of expense, but the Chief was continued in this configuration for 3 years.  Making these changes for the Scout was not practical, so it became the forgotten child as the 31 model year ended.   Of course, the Chief and Standard Scout then used the same primary drive cases and gears through 1933.  However in 1932, the generator drive for the chief platform was moved to the rear of the primary drive case, same as 101.  This required yet another change to the primary drive cases to accommodate the generator drive.  Indian could have saved a lot of expense by simply making the 32-33 cases, put them on the 31 Chief and blank out the generator drive for that 1 year.  All of this generator drive stuff for 31-32 is because the Chief still used the Splitdorf generator in 31, even though the Scout and 4 were fitted with the Autolite generator in 31. The Chief generator was mounted under the magneto and driven off the timing gears through 1931.

This is mostly Chief info of course, but I find it very interesting to see how it all fits with the Scout and 4 in those years.