trying to perform leakdown test on my hp500. tried to put at TDC but when i start to fill cylinder it pushes piston back down, try to hold crank but after 70 lbs or so cant hold it. everything i read says test at TDC except instructions with guage from summit says bottom dead center. tried that also but cant seem to get both valves closed either leaks through exhuast or intake. it has billet pulleys on it so no crank bolt without removing safety wire and pulley so im turnig with prop shaft. , i've looked on line and it looks simple. what am i missing????