I bought a Mercier Kilo TT last month and it has a 1" steerer tube. I bought a 1 1/8" bmx stem and a 1 1/8 shim so that it would fit. I went into it thinking it would be a simple task, but I was wrong. I can't get the stem to stay in place. It doesn't matter how much I tighten it. How far should the shim be inside of the stem? Any help or tips would be much appreciated. I'm pretty new at taking apart/reassembling bikes. Thanks!