Setting the gap on OHV Troybilt Pony 17.5hp.

I need help with adjusting the valves on my riding mower. I have sought out extensively the gap to set the valves, with varied opinions. I have tried to find TDC of the (I believe horizontal piston) with no clear instruction. The motor stops turning at compression point and I have not succeeded in a remedy. Is there anyone who can help me,I do appreciate your time and help.



Here are my specs:

model Number: 13AN77KS011/211 - Troybilt Pony 42inch

Motor:12 0511 ZA 23647 - Power Built 17.5 Gross HP 500 CC