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Hello- > > It's not as much as you think... if it were such a major problem, then the > > flywheel endplay of a typical modern EFI engine would play hell with the > > flywheel-mounted crank position sensor, but it doesn't. > > That would be, as you mentioned earlier, because these magnets are mounted at a > much larger radius. > > The magnetic field error would amount to only a small amout > of the total circumference of the flywheel circle. That is why this is done on > the flywheel rather than in the distributor. You're talking about distances in different directions. It'd be like describing how well centered you are in your lane while driving by discussing how much further ahead your car's bumper is than the guy in the other lane - its the distance in the opposite direction we need. The radius effects how much a given tolerance effects timing. In other words, if magnet placement is 0.001" off with a radius of 3/8" (kinda like Pertronix), that's _16_ times worse than being 0.001" off with a radius of 6" (kinda like a flywheel). The actual distance between the sensor and the magnets is on the order of ~0.050" or so. Crank endplay can be roughly 5-10% of that measurement, which is significant. However, distance effects the _strength_ of the hall-effect pulse. But, you don't time based on the strength of the pulse. You time by finding a transition point in the primary hall effect voltage signal (well, actually, this is a slight oversimplification... but the exact method is much more complicated to explain but gives the same danged result). Guess what? No matter what the distance, it is at the _same_ place - when the sensor and magnet are right over one another. End result? So long as the sensor isn't so far away from the magnet that the signal is too weak to be seen, it really doesn't matter. What _is_ important is the accuracy of magnet placement on the spinning disc. Good mfg tolerances help. A large radius helps. Take care, Shad Laws LN Engineering http://www.lnengineering.com ------------------------------------------------------------------- List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org