I think that the general rule of thumb is no more spacers than 1 - 1.5 x the steerer tube diameter. So, a 1" steerer tube could have 1 - 1.5" of spacers below the stem. If you mean that there are 4cm above the stem, then aside from looking a little bit odd, I don't think that there's a problem with it. Just make sure you put the top spacer so that there is about a 2mm gap between the steerer tube and the top of the spacer. That will let the headset cap tighten down properly.

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Brandon Marsh - Website | @BrandonMarshTX | RokaSports | 1stEndurance | ATC Bikeshop |

None, as long as you have the proper gap for the top cap to make the aheadset adjust properly. If I am unsure of my steer tube length, I typically run the steer tube between 30-50 taller than where my stem is.