^... gets my vote every time, even when I've got the head off, engine on the bench and a perfectly good dial gauge + bracket hanging on the board. I don't like the roll-over factor of a dial gauge when compared to the certainty of a positive stop. Last time we had this debate I think it was Harry Barlow that pitched in with the fact that the Nascar team that he worked for in the USA would ONLY allow the positive stop method to be used..... and you can't get better than that! The best bit about this method is that you just need to pop the plug out, insert a stop, mark 2 points accordingly on the mag housing lip, slip a sheet of paper between the mag housing and the flywheel, run a pencil or pen around the lip to mark a straight reference line between the 2 points and mark the 2 points also, hold up to a light source, fold mark to mark along the line. slide this back in between the flywheel and housing lip.... and the centre fold is TDC..... SIMPLE! Mark TDC on the mag lip with a pencil, then do this again with a stop of a different diameter as a check. Regardless of diameter, and resulting 2 stop marks, the mid point should again be where you have already marked as TDC will always be TDC. You can do this as many times as you like, until you feel sure that you've identified TDC correctly, then use a fine bladed screwdriver to tap in the final confirmed TDC mark.rosscla wrote:If you use the positive stop method you don't need to take the head off, though if its been seizing then a strip and check would be advised.
Put something like a round punch or large screw driver in the plug hole and strap it in place, turn the engine in one direction slowly till it hits the stop and mark the mag flange next to the arrow on the flywheel, then turn it in the opposite direction till it touches the stop again. Mark this point on the mag flange. TDC is midway between these two points.
To find the correct firing point you can simply measure the required distance around the edge of the flywheel, measurements can be found in various texts and probably by doing a web search.... or by doing some maths.
NB: Never trust an existing TDC mark (or firing point marks) as a change of crank of mag housing will cause an earlier mark to be out of position!
Adam
you have to dismantle the flywheel and line up marks on the flywheel and flange and then if necessary move the stator so that two white lines in the window line up with one on the pickup 
