I have had this Tamron lens for a while. It is a good lens for the price but it had shown its problems like over exposure in flash shots. I received a replacement that was slightly better for the over exposure problem. However the lens soon developed a wobbling front end problem. The piece that holds the lens hood started to wobble and I even noticed that the front lens element can move back and forth. Eventually I saw the backside of the front element touching the surface of the lens behind it! There were fine pieces of white dusts that I thought were small broken glass pieces.
The lens was in still in warranty and I could certainly send it to get it fixed. However I hated the long wait time and I had to pay the shipping. So I searched online and found other people reporting similar wobbling front end problem. The fix (like this Youtube video) seems to be easy enough. So I removed a plastic ring and tried to tighten the three screws. It helped but it didn’t completely fix the problem. The front end was still slightly loose and the backside of the front lens element could still touch the lens behind it. That was a couple of years ago. Since I didn’t find any issues with image quality, I just ignored the problem.
Recently I was trying to get my stuff ready for a volunteer photographer role. I decided to take another look at the problem. So I removed the plastic cover and proceeded to remove all three screws. After that I could remove the front element. I took the opportunity to clean the inside of the lens as much as possible. Although the lens surfaces touched but no permanent damage appeared to have been done.
I then proceeded to put the parts back and noticed that the front element assembly is held down to the base by the screws. Each screw goes through a slot on the front element assembly. The thickness of the slot is like a wedge, one end is thicker than the other. At the thin end, the screw is too long to hold the front element assembly down completely. By rotating the front end element, it is possible to tighten the screws, and most importantly, create some extra space between the front element and the lens element behind it so they no longer touch each other.
At the end, I was happy to have fixed the problems. I was curious why the lens was designed that way but I could find a good explanation.