Warping in first layers (Prusa Mendel i2)

Hi everyone.

I have recently been encountering an issue of warping of my first layers, predominantly on my y-axis.
I have a Prusa Mendel i2, and my heating bed is problematic, as it heats up only half the bed (roughly from y=80mm to the end of the bed). The issue I am having appears predominantly on the first layers.
I printed a small object (toy truck) to check whether i was having this problem only in larger prints. It appears not as you can see in the attached images:



Does anyone have any suggestions on what may be causing this and how I could solve this issue (aside from buying a new heating bed which is on the way)?

The print was made with PLA @ 187 Celsius, 0.2 layer height and Bed temp @ 50 degrees Celsius (which again is not exactly accurate as it is more like 70 on half of the bed and 25-26 on the other half so that the thermistor at the middle of the bed reads 50).

Update:

So I tried printing the same print in blue tape (that is: no heated bed) and the result is exactly the same as before...

Can anyone suggest any possible solutions to the problem?

So I managed to fix my heated bed and it works fine now.
The problem does not seem to go away though:

Here is the finished print of the same toy truck (quality has increased considerably. Moving parts moved immediately upon removing the part from the bed!) and here is the persisting warping.

I also tightened my y-axis belt which seemed a bit loose.

Any other ideas anyone?

Edited 1 time(s). Last edit at 10/14/2014 04:34AM by Hlias.