I recently changed a bent valve and putting it back together I can not get the timing chain to stay tight. I lined up the timing mark(I) for TDC. then I put my cam shaft in with the holes facing up and the marks on the sprocket are even with the head. I put the timing chain tensioner back in and put tension on the chain. I bolted down the camshaft cover and gapped my valves. and as soon as i rotate the crankshaft the timing chain busts loose and has no tension on it what so ever. Does anyone know what I am doing wrong?