Originally Posted by
oneclick
Go backwards - if a right-threaded cup, place it in the shell and turn anti-clockwise with light pressure. When the cup gets to a point it will drop inwards one thread and that's when you know you have the start.
For damaged threads there may be more than one point where the cup drops. Check the cup visually as most often the original threads will still be there, and hopefully they are still deeper and better formed than whatever damage there is. Go around several times and decide which point has the best-feeling drop - size, and at the moment after the drop look at the alignment. Use that.
Yeah, that's the standard working theory for this, not always that straight forward and not for the inexperienced.
Not always, that's where many make their mistake, if the starting threads are only half good after a rework, they can get you in more trouble so caution wins the day.
If you screw this up at the drag strip, you don't make the next round, I never missed a round in 25 years.
Never had to pull a motor or transmission out or apart either for this in 35 years, 25 professionally.
