Please Help!?

I just put a water pump in a 98 Mitsubishi Triton 4cyl petrol due to it leaking. You had to take the timing cover and belt off to get to the pump. I put it all back together but it wont run. When it winds over it sounds like its got very low compression. However it ran fine before I started. I'm thinking it might have bent valves. I have a compresion tester but i cant fit it down the tunnel in the tappet cover. So anyone know what I can do to check or anything? Please help