Issue with the Connect Line Tool

[micheus]

That guide for fixing the front wheel was perfect, if you have the time do you think you could help me out with the back wheel? I tried to follow the same steps, but it just doesn't look 100% accurate to the front.

Image: https://www.dropbox.com/s/l1xl6w1oskpluk7/9.png?dl=0

Yeah, I can try (for tomorrow )
Supposed the rear wheel is going to have the same size the front one, maybe the first step would be ensure the two "gaps" have the same size. Then, ensure they have the same amount of segments.

Please take a look at my smooth preview image and yours. It seems your forgot one step near to the end of the gif sequence which the initial edge loop created at begin was "rearranged" and had the up edges removed and the vertices was connected to reorganize the mesh. Also, it seems you added an extra edge sequence to the top:

If you see that kind of discontinuance on the mesh in Smooth Preview mode, then something is wrong and you need to review your work.

One final question:
How did you create that perfectly fitting wheel? And not exactly world threatening but why is it a different color to the rest of the model in that attached image?

First I checked the max diameter it could have by selecting two vertices in from the bottom of the "gap" - it was about 0.81. Then I create a cylinder with a radius of 0.4 (0.3 for the height and 14 sessions because you can count about 7 segments in the area for the wheel we just created)
The color is different just because my Theme uses default material as blue.