Yea, you probably are at 180 degrees out. You probably had the piston set at tdc but on the power stroke, not the compression stroke.

Only damage you could have done would be to the intake manifold. I've seen them crack due to the backfire, or blow the gasket out.


Easiest way to find TDC is to put your thumb over the number one spark plug hole, rotate the crank until you feel compression. Then CAREFULLY stick a screwdriver in the cylinder, and feel for the piston to come up as far as it will and then start to go back down, rotate it back so its all the way up, and then line up your 0 degree timing mark on your crank pulley.