Custom kernel for Android

I have a HiKey Lemaker 2Gb board. I would like to build some custom kernel for Android, to enable some drivers. The problem is the board does not boot with the custom kernel.

I follow the instructions from here to build the kernel:
http://source.android.com/source/devices.html#running-android-hikey
The kernel builds fine. Then I copy the Image and hi6220-hikey.dtb files to the device/linaro/hikey-kernel/ folder in the Android source tree. Then I recreate the images by calling the following commands:

. ./build/envsetup.sh
lunch hikey-userdebug
make -j8

Then I flash the generated images to the board.
Everything works without error, but the device does not boot. I also tried this without changing anything in the kernel configuration. Any idea what do I do wrong?

Br,
Istvan

Problem solved. All instructions talk about 4.1 kernel, but actually 4.4 is needed. When I switched to 4.4 branch it started to work.