A few weeks ago I landed just a bit too hard after coming off a jump and bent my Crank arm. The chain side. It just had Shimano Alivo cranks. So I replaced them with the same ones. They were supposed to be the same lenght, but as soon as they were put on I had to raise my seat by about a half inch. Now, the front deralier isn't shifting right. When I'm in the 8th gear in the back and the middle in the front, it won't want to shift back down in the front. I have to change the gears in the back for the front to shift back down. I took it down to the shop that put the cranks on and he told me that it wasn't ever ment to shift in the gear combo. I did however notice that the new cranks have a hyperglide sticker on them. I know it has sram cassett on the back as well as a sram chain. Did this shop sell me the wrong kind of cranks?
Actually, the shop is right about using that gear comvo. It's called cross chaining, and tends to accelerate wear on the components because the chain is running at such a severe angle sideways. Step behind the bike, when it's in that combination and you'll see what I mean.
That sais, the new crank may not have fit on the spindle EXACTLY the same amount as the old crank.
You could probably turn the FDER L screw out 1.4 turn or so. Too much, and you may be throwing the chain off the small ring in other combos.
Another possibility is that the cable doesn't quite have enough slack, but I would play with the L screw first. Just don't get crazy with it and KEEP TRACK where it's initially set. You may have to return it to that spot.
And really, you DON'T want to use the extreme chain angles if you can avoid it. That's why you have all those gears. Think of your bike as really being an 18 speed.