[Razorback1980]

I'm not sure what the tolerance is, but I know what the starter sounds like with bent valve(s). It whirls like you have no compression. Either test your gauge on another engine or get a second compression gauge, that will tell you the story. I am guessing it will probably measure the same as the first. The compression was probably so low that it never measured on the scale. If you pulled the cam tower back off, you could look at the height of the valve springs and that should tell the story for sure without pulling the head. Not sure of any other way to confirm it. Compression has to be good for the engine to run.