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On 5 Mar 2003 at 23:01, Mark Seaton wrote: > When I recently checked my timing, for some reason I clipped the pickup onto > the other leads as well and discovered that no.3 read 5 deg adv as opposed > to the 7.5 deg of no.1! I had heard that this was a rumoured feature of our > engines as it would make no.3 run cooler. Thing is, I'm using a Pertronix > contactless ignition module! So what could this mean? Is it possible that > the pertronix magnet ring has a diplaced magnet for no.3 (there is no > orientation marking so it would be pure chance that it ended up in the right > place!) or could it be that there is a mistake in my magnet ring which again > by chance I fitted in the right place? Or perhaps the Pertronics relies on > the lobes of the dist cam to control the magnet flux so the timing is still > controlled by the cam? Anyone know? I think the real weakness of the Pertronix is the virtual impossibility of controlling the magnetic fields well enough to give consistent timing signals. I believe what you are seeing is just normal variation of the Pertronic system. This has always bothered me, because it is notoriously difficult to control magnetic fields in general, and permanent magnets in particular, plus these sensors are working in the fringing fields of the magnets where the field strength is a very strong function of the distance. So a small amount of radial play in the shaft can have a huge effect on the timing. I never thought about using the original cam lobes to help shape and control the Pertronic PM fields. No doubt there is some effect, but I'd be surprised if it was useful. Interesting thought, though. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ------------------------------------------------------------------- List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org