i just finished up a head gasket job yesterday, even after fixing a code 51 i still have a wierd hard starting, it sounds like like cranking with kinda random pausing, its even clashed with flex plate while starting a couple times. once it does start it wont stay running and has a choppy idle. i checked timing earlier with the cam gears pointing at 12 the crank looks to be sitting at maybe 4 degrees but i dont see a mark to say whats tdc 0 degrees. can anyone shed some light on this?