I tried to be a "mechanic" and didn't really know what I was doing. It's a 105 dereailer, and I took the two screws out of the top of it, hoping I could turn it just slightly because the chain was rubbing on the left side of the derailer while I was on my tallest gear in the back.

After realizing that I shouldn't have messed with the two screws at all, I can't get one of them screwed all the way down. It only goes 90% of the way down, and I've kind of stripped it. And therefore, my front dereailer won't even shift at all. I can't even move the lever.

However, with both of the screws not even in there, it shifts just fine. Why is that so? And how much harm will I do if I leave them out until Monday when my LBS can get it in to look at it? I'm hoping to still be able to do a couple more rides.

What you have done is removed the stops on your front derailleur. IF you use it as is, you stand a very good chance of shifting the chain off of the chainrings. If you shift from the large ring to the small without the stops set correctly, it is possible to drop the chain off to the inside of the crank. If this happens, you will possibly suck the chain up into the rear wheel which will probably destroy the rear derailleur and bend the hanger. It could also break some spokes on the drive side and destroy your wheel. Also, the chain getting sucked up will probably score your right chainstay which could ruin your frame if it cuts deep enough. I wouldn't ride it with the stops on the front derailleur messed up.

First and foremost, you get a little LOL. (but only because I've basically done this before)

Anyway, those screws are only "limit" screws that stop the derailler from going too far in either direction. (one screw for each direction).

The reason it won't shift at all with them both tightened down is that you've basically set the lower limit and the upper limit to the same thing, so there is no room for movement.

With both screws completely out, it should shift, but it's very likely that you'll throw your chain off the chainrings when you do it.

It's safe for you to just put the chain on one of the front chainrings (with your hand) and not to use the front derailler until you either get it sorted out or take it to a shop. Your back one should still shift fine.

Actually, to adjust what you were trying to adjust in the first place, you need to loosen that "other" bolt that attaches the entire contraption to the frame. You will be able to move it in either direction that way. But be careful, because you'll also be able to move it up or down with that bolt loose, so you may want to mark it with a piece of tape or something like that.

lol... I'm a knucklehead. It seemed as easy as putting two screws in... and I can't even do it.

Yeah those screws don't need to be all the way tight either. Since you said you stripped them out you may need to replace the screws or get a new FD.

There are lots of nice manuals online on how to adjust the FD, but basically you want to shift to the big cog in back, small ring in front, loosen the cable with the barrel adjusters until the cable is loose. Then set the low limit screw (the left one on the 105 I believe). You want the derailleur cage to just be almost touching the chain on the left side. Now that that's done shift to the small cog on the back and pull the wire tight with your hand. The FD should move over and push the chain up onto the big ring. You then set the right screw. You want the derailleur cage to almost touch on the right this time.

After this is done take up the slack with the barrel adjuster until the cable is taut.

Oh and by the way Shimano's website has all the manuals for their equipment online.

Step away from the bike. Step far away.......
Then have someone else load it into their car and drive it to an LBS to have the front derailluer adjusted.

^^lolled, but in a harmless kind of way... thinking about my own moments over the years.

unbelievable. you clearly have access to the internet (who doesnt?) why the hell would you just start pulling screws out of a device you know nothing about without first at least doing a quick look-up on how the thing works?

the others have covered what you did wrong, take this as an opportunity to read the park tools site or the shimano site and fix what you messed up, it will be a learning experience for you, dont just walk into the bike shop with your tail between your legs and admit defeat, man-up and fix your own mistakes, this isnt rocket science here.

As funny as this thread is....I don't think there is a person alive who didn't tinker with something then royally screw it up because they didn't know what they are doing. Not me of course...

The park tool website is a great resource. I use it myself and feel a whole lot smarter after reading it.

As slowandsteady mentioned above check out Park Tools website. Here is the link to the Park Tools Repair guide website:

https://www.parktool.com/repair/

I found the website to be better than their book.

i just learned to do this myself. it's easier than you might think.

https://www.google.com/search?client=...UTF-8&oe=UTF-8

just watch a few of those, and you'll see that adjustment is easy.

one rule of thumb for bike maintenance: brute force is never the way. if something won't go in all the way, it's either in wrong, not greased, or it's not supposed to go in all the way.

Yeah, I was going to post some simple der adjustment links and advice, but I think it's best to let your mechanic show you how to do this in the future. After he/she shows you and you pay for the adjustment, I advise you to take the bike off the stand, loosen the cable clamp and loosen the frame clamp completely, then start from scratch on your own, so you'll know how to do everything. (Do this practice while you're still in the shop)

Align der (up/down and rotation)
Set lower limit
Adjust cable
Set upper limit
Test and minor adjust cable

This post was by far the best advice given to me in this thread, and I very much appreciate it. I was able to fix it on my own. I won't know that it's 100% fixed until I take it for a longer ride. I screwed the lower limit screw almost all the way down. But the screw on the right I found I had to loosen quite a bit. I started with it all the way down, couldn't move the shifter. I loosened it quite a bit, then a bit more... then a bit more until the chain smoothly shifted from the little ring to the big ring.

I will probably take it to work with me tomorrow on my commute to make damn sure I have it dialed in right.