The starter reduction gears used on the Honda 250ES BIG RED went through a few design changes during their production run between 1985 and 1987 (US). I am writing this post to provide some information on the changes that I have noticed. Since I don't know all the factors of the changes that could of happened I cannot be certain on part interchangeability between the 1985 and 1986 designs. The 1987 design is different than the 1985 and 1986 per the information below.
The 1985 250ES starter reduction gears are on the left and the 1986 250ES starter reduction gears on on the right. As shown the shaft is larger on the 86 and the gears are thicker. The gear ratios are also different between the two. Notice that even with the changes the it appears that they could be interchangeable.
The image above is marked up with some approximate measurements that I have taken. The gear ratio between the two shafts for the 1985 250ES is 1.6875 (27 teeth / 16 teeth). The ratio between the two shafts for the 1986 250ES is 1.3888 (25 teeth / 18 teeth). So the design changes in 1986 250ES decreased the torque from the starter to the flywheel but increased the speed as compared to the 1985 250ES. I wanted to share this as the part diagrams and numbers for the 85 and 86 don't show the differences.
Assume starter torque is 10 ft-lbs and the starter speed is 50 RPM (these are just made up numbers for the calculations below)
1985 250ES - Torque to the flywheel would be 1.6875 * 10 ft-lbs = 16.875 ft-lbs
Speed output to flywheel 50 rpm / 1.6875 = 29.63 rpm
1986 250ES - Torque to the flywheel would be 1.3888 * 10 ft-lbs = 13.888 ft-lbs
Speed output to flywheel 50 rpm / 1.3888 = 36 rpm
I don't know why the changes were made in 1986. Could it be the 1985 parts were not strong enough? Did the starter specs (torque) change from 1985 to 1986? Not sure. I am also not sure if the complete starter reduction gears and cases are interchangeable. You would think that if Honda was to make a design change it would require minimal changes to reduce complexity and cost.
The 1985 gear is on the left and the 1986 is on the right. The 1986 gear is thicker but there is an undercut so the height can be used with the same case.
1985 is on top and 1986 on the bottom
Additional picture of the gears and case. Note the thrust washer on the left side.
There was a bearing added to the reduction gear for 1987. This design is not interchangeable with the 1985 and 1986 as seen with different shape gear reduction case.
