Hi,

I have an electric folding bike which is fairly new at just two months old.
It's got 8 gears. The derailleur is a Shimano Altus. The rear shifter is a Shimano SL-M310 8 speed.
Anyway, here's the problem:

I set the gear to 1 and pedel a bit, and it gets there, but then, for as long as I pedal, the chain moves from 1 to 2 gear non-stop, every second or so. So essentially, I can't use 1st gear, but only 2 and upwards. Also, it never changes to 8 gear (the smallest cogwheel), so whether the shifter is set to 7 or 8 gear - it doesn't matter. The chain stays on the 7th gear.

The bike is still under warranty, but if I can avoid having to go to the shop (which is a bit far), then please let me know how to do this.

You need a rear derailleur adjustment. Assuming that it was never right it could be either a limit screw adjustment or a cable tension adjustment.

Since your bike is so new, I'd advise taking it back to whoever sold it to you. If you want to tackle fixing it yourself, go to the Park tool website and find the instructions for installing a rear derailleur. If you decide to do that, don't mess around. Completely disconnect the shift cable and start from the very beginning. Follow the instructions IN ORDER and don't skip any steps.

Considering I never done it before, how long would it take to do that? Also, is it what's called "indexing"?

How mechanically inclined are you? Your first attempt could take any amount of time. I've never done anything in my life that I didn't think I could do faster and better the second time.

"indexing" means the shifter has little steps that match the exact amount of cable pull necessary to shift the rear derailleur into the next cog. That means you can shift to the next detent and the derailleur will snick the chain onto the next cog. Naturally, you have to have matching parts, everything has to be aligned as new, and the cable adjustment has to be right for indexing to work.

Park Tool Co. » ParkTool Blog

Any where from 5 minutes to 2 days of cursing.

A basic understanding of what the limit screws do, and what "cable tension" means will get you most of the way there. It's really pretty simple. Some people prefer to turn screws and adjusters at random, and they fall into the "days of cursing" category.

Very briefly:
The limit screws control how far the derailleur can move inwards & outwards.
The Low limit "L" controls it's ability to reach the lowest (easiest) gear. Bad adjustment means you could shift into the spokes, or not even reach the biggest cog.
The High limit "H" controls reaching, or not, the highest (hardest) gear. Bad adjustment means you can overshoot, or not reach the smallest cog.

"Cable tension" is fine tuning the position of the derailleur so that when the shifter is in '3' (for example), the derailleur lines up with cog # 3. If the derailleur is a tiny bit higher or lower than cog #3 , you will get noise, bad shifting & poor performance.

Read the Park tool section, maybe watch a few videos, then come back if you have specific questions.

I think I'll leave it to the pros, and if it happens again anytime soon, I'll learn to do it myself. Thanks for the comments!

Hello again. I went to the bike shop and they told me I should leave the bike and it will be ready in 3-4 hours. The bike shop is not near where I live, so I couldn't leave it there because I needed to use it that day.

So, I'd rather just do it myself. On the Park Tool website, I see this special tool is listed as a prerequisite:
Park Tool Co. » BT-2 : Cable Stretcher : Brake Tools

Do I really need it, or is it possible to do the whole derailleur thing without special tools?

You don't need the tool.

OK, I played with the screws a little bit and got the derailleur to move the chain to the first gear (and then to the spokes, but I fixed that). Now I need to make it able to to move the chain to the highest gear (smallest cog), but I noticed something, which I don't think happened because of my playing with the screws. The derailleur looks awkwardly placed. Here's a photo:



As you can see, its angle is just weird. When I look at a photo of my bike on the seller's website, it looks "normal", like other bikes:



Is it one of the screws that controls it, or is my derailleur bent or something?

EDIT: My bad, it appears to have to do with the gear the bike is set to. It looks normal on the lowest gear. HOWEVER, while I did get the derailleur to move the chain to the highest gear, I can't make it KEEP the chain there. When I pedal, the chain tries to go back to a lower gear (7th gear out of 8). What screw should I play with?

Also, when I play with the b-tension screw, nothing seems to happen as far as I can see.

Somehow, that does not seem like the prescribed procedure.

Probably the only thing you ever needed to do was "play with" the little black knob.

You mean the cable tension? I did try that, but I still can't mange to keep the chain on the smallest cog.
The derailleur looks bent to me. What do you think?

Of course it's bent. The pulleys are bent inward and twisted as well - likely the derailleur hanger (from an impact due to a fall to the right) or could be the derailleur itself is bent/twisted (both are possible). Need to correct hanger alignment then readjust. The info we needed that nobody asked was when the problem started and what immediately preceded it. I would guess the bike fell over or something got caught in the derailleur/chain.

Yes, it makes sense. The bike fell to the right due to very strong winds (I left it standing on the jack for a second while I was collecting the dog's poop. It fell immediately).
I hope the warranty covers it.

Edit: Then again, I was having gear problems even earlier, but now it's worse. The chain falls off the front chainring when I pedal backward (but not only then), and the gears started acting even weirder since that fall.

The shop would have to do it as a courtesy, as accident damage is not covered by warranty. I would think they'd at least not charge for the derailleur adjustment, or maybe discount the straightening. You are very lucky that you did not shift the chain into the spokes right after the accident. It's always important to look over your bike and check operation after any incident of that type.

There's no guarantee a chain won't come off when pedaling backward. It's more likely when on the largest or smallest cog in the rear.

So far, they were nice enough to replace the bike's LCD computer after I shorted it by connecting the headlight's wire the wrong way, and they also gave me a new USB charging cable after I told them the old one was stolen (I was willing to pay for it, but they surprised me). I hope they'll be just as nice this time.

Hope so, but you may be starting to stretch their patience and good will.

Thank you for posting pictures, as that really shows the problem.

Some people looking for help let things go on for pages before it gets figured out.

Can't tell from here if the frame hanger (where the derailleur attaches) is bent, or if the derailleur is bent, or both. Hangers bend most of the time. Is your frame steel or aluminum ? Steel can be bent back easily (most of the time). Aluminum is not very forgiving and often cracks when trying to fix a bend.

The shop replaced a bent piece of aluminum (not the derailleur itself) for 30 bucks. The chain doesn't fall and I can use all the gears now, but they feel so much stiffer. Also, even when set to the biggest cog, the derailleur isn't "straight" like it was yesterday before the fix. That's weird.

If it works properly don't worry about what you think is an issue.

But it feels tough on my legs. First gear doesn't feel as easy as it was before, and changing gears is harder too - when I lower a gear, it actually becomes harder to pedal for two seconds, and only then the gear is lowered.

What the shop did was replace the derailleur hanger. It is a separate part and it protects the bike by being replaceable. It did it's job.

Sounds like possibly a perception problem. Do you pedal gently when shifting gears?
It does take a little time for the chain to move over to the next cog. When shifting the pedals need to be turning but very little pressure on them. One also does not shift going up hills, because of the pressure on the pedals. One shifts before the hill. being in a gear where you can pedals at a relatively high speed, with not much pressure on the pedals will speed up shifting time.

If it shifts properly, as already mentioned, the derailleur problem is fixed. Harder on the legs could just be perception or an unrelated problem like low tire pressure.

Maybe you need to charge the battery.
Or just bend the derailleur back the way it was.

If by "tipped" you mean the bottom pulley on the derailleur is closer to the front of the bike when viewed from the side of the bike, then it's OK. As the chain shifts to different size cogs the slack in the chain is controlled by the position of these parts. In other words, nothing is wrong.

I know when and how to change gears, and that's not the issue. The real issue is that pedaling feels harder now.

trailangel, I am talking about pedaling without the battery (in both cases).