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I've worked out WHY that problem of getting one end or another, rather than the middle of the timing adjustment happens. Though the gear to the jackshaft has 12 teeth, the oil pump drive only has 6 sides, so the dizzy will only drop easily in 6 places. So the tendency is to fit it where the dizzy drops, meaning you often skip the correct tooth on the gear.
I don't understand how that works Steve. The 12 teeth of the dizzy gear are directly meshed to the Jackshaft but the oil pump drive, although only having 6 sides, is free to rotate 360º, so it's position is irrelevant.
Yes it's free to move, but the drive socket in the bottom of the dizzy is only a hexagon like the drive rod. So if you drop it VERTICALLY (and this is the key point) onto the drive rod 30 degrees out of synch, as is possible exactly as often as not, it will baulk! It can't turn to engage as the gear teeth have already partially engaged with the jack shaft and there's not enough wriggle room in that engagement to allow the drive rod to turn the 30 degrees and no rotational force at all acting on the drive rod to make it want to line up.
So most people pull the dizzy out again and try for a point where the dizzy WILL drop in easily and hence go 30 degrees the OTHER way from correct and miss the sweet spot in the centre. I've done it myself, many times, before I worked out WHY I couldn't get it right. Now, it's easy! TBH, until I saw it in these pages, it never occurred to me to to turn the jackshaft, far too much like hard work!
Maybe if you are doing it with a warm engine, or one that has no oil in the pump for whatever reason, the resistance put up by the oil in the pump might be easier to overcome and the drive rod easier to slip round. But most people, you and I included, are more likely to pull the dizzy just to wind oil pressure up manually on a cold motor before starting it for the first time or after a long layup. Thus increasing the resistance in the oil and making your own life harder! Of course, you STILL only have a 50% probability of getting it wrong! I guess it's just a case of "do you feel lucky?"
Steve