THE ROAD TO HELL
Splitting headache: The crack (at 2 o’clock) means the head’s a doorstop. Overtightening the head bolt, between the exhaust ports, is a common cause.
No return: The tight cam ring prevented the ignition advancing properly. A hand scraper is a gentle way to remove tiny amounts of metal to achieve the correct clearance.
Down the hatch: Aaaargghh! escaping my grasp, this nut rattled down the hole, quicker ’n a rabbit. Thankfully it didn’t wedge in the cam gears and the magnet pulled it out.
Polish it off: This is a witness mark from where the piston was still contacting the head. Removing a bit of material with a burr in a drill finally restored the clearance.