Leaderboard

Up should be the least pressure. When it starts coming down, that's when pressure is applied. Most engines have some sort of mark that indicates TDC. You might research that. The screwdriver method works too ...usually. The problem with the screwdriver method, is it's a judgement call, and not perfect. But it sounds suspiciously like maybe we're not quite at TDC. Just based on the symptoms, and subsequent description of same. If there's no marks, at all, then try adjustment of the valves by rocking the engine. Look for the sweet spot, when the slack in the rod appears. Because that's likely where your tap is. Adjust that to tolerance specs. See if that improves the situation.

You might try to find a leak down tester at the local auto parts tool loan program, and give that a try. Otherwise I'm assuming that there's not any oil leaking around where the cylinder meets the case. And if you pull the dipstick while its running, and oil doesn't come out. Nor is there any oil on the crankcase ventilation tube. That pretty much covers the head gasket. I'm still thinking that one of the lifters is the problem, but it's a good idea to keep an open mind. If it makes good power, and the plug is still looking good, and as long as it doesn't get worse. I'd just keep driving it for awhile. Always keep an eye on it, and keep checking the plug. If it's anything significant then eventually it'll start showing signs of what's wrong with it.