Youre right. I did know this, but when I looked at the picture on the 'lotus' link above, you can see a very wide, straight cut gear, which from a quick glance I took it as the newly cut 1st gear you get on uprated shafts. I just went and checked a few standard shafts in my workshop and the reverse gear on a standard input shaft, the width is very small in comparison to the one in the photo, like only 13mm or so wide and that one looks almost like 30mm+ in size! Hence I thought it was the straight cut first. Interesting to notice these differences in shaft design. But I see what you mean now about the synchro reverse gear.Hi Bruce, no it doesn't. All primeshafts , whatever the UN1-XX versions were all helical and with the same ratios.
The only straight cut gear is the reverse. Maybe, what you consider to be the first gear is the reverse one, as it is a bit different than the earlier versions : teeth stand over a wider surface on the shaft because ont these UN1-XX versions , reverse gear is synchronized.
Just thinking, I went and had a a look in one my assembled box with uprated shaft, and there is plenty of room to have the reverse gear teeth wider as seen on the shaft in the photo link above. I did also notice, that the uprated shaft did not have the straight cut reverse gear made wider along the shaft, but cut very narrow as the earlier boxes are.
I also have this other theory, that this is also the narrowest part of the whole shaft. And having the gear teeth spread out further along the narrow part of the shaft like that, would make the shaft stronger with less flexing less about that area. Maybe that was one of Lotus's 'strengthening upgrade' ideas as well?? Bugger - I should have had mine made up like that!