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Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Mike Canter, Feb 2, 2016.
What about a larger diameter trigger wheel?....
I'd consider the FIE setup as the components are encased in epoxy. When I used it, it worked great. That is until I broke a belt and the belt cleaned off the wires, lol. I start mine on 12v with a cheapo starter and it works fine until you get the phase off when using the crank trigger.
I agree the Mag trigger produces a higher amplitude signal because of the smaller diameter internal wheel allows for the magnet to move across the pickup at a faster rate than with a 7" crank wheel and trigger. The problem can be with the magneto as the trigger that the timing can fluctuate half to a whole degree on a good Mag drive. That much variation or fluctuation really changes the tuneup.
TOL, a larger diameter trigger wheel makes the problem even worse on signal amplitude
Wouldn't the periphery speed be higher for a bigger diameter wheel at the same RPM?.....
Not in reference to the magnet passing the sensor
Okay, I'm still not getting it. Maybe you can clue me in offline?....
With a blower starter we have "just" enough cranking speed to get the job done starting on the trigger. The on board deal is a little closer to the wrong side of the edge than a blower deal. All it takes is something being off and it is not going to start on the trigger. I agree with Scott, there has got to be a way to design a removable switch. Downside, another potential component to fail.
The milspec or push/pull switch like a mallory may work.
This thread is proof of why we have the lame trigger setups on our cars.
Apply bandaids until the engine will make noise.
I could never get an answer for why the magneto trigger is so powerful.
They are both an a/c generator.
There is a noticable amplitude difference between trigger types and gaps.
The closer gap increases the amplitude and low speed generation for starting but carries a noise penalty.
I can tell you that the Lahey trigger makes the most voltage but we seemed to get the cleanest signal with the MSD type with stainless jacket.
The amplitude of the signal is based on the speed of the magnet making and breaking the magnetic field that is felt by the sensor. The Mag has a small diameter wheel as compared to a crank wheel so the magnet on the Mag moves faster across the sensor and therefore a higher amplitude signal
There has to be something else affecting the signal. The crank magnet moves past the sensor at a much higher speed than the mag. First of all the crank wheel is spinning at twice the speed of the mag in RPM alone. The surface speed of a 7 inch wheel is approximately 146 inches per second at 200 RPM cranking speed. A 3 inch (estimated) mag pickup surface speed is less than 16 inches per second at 100 RPM (1/2 crank speed) The crank magnet is therefore spinning over 9 times faster past the sensor. Please correct me if I am wrong.
I believe the mag uses a reluctor ring and has twice the number of triggers than the crank to make up for the half speed.
DMy math was wrong on the crank magnet speed. I accidentally doubled it. Even correcting for that it is still a much faster magnet speed. As for the mag, it has 8 versus 4 in the crank. I could be wrong on this but I believe the mag has a larger fixed magnet and the reluctor wheel passes through the magnetic field whereas the crank has the magnet pass through a non-magnetic pickup. The mag pickup is a stronger signal but less accurate in relation to the crank/pistons due to gear slop, etc. The crank trigger is weaker at slow speed, but more accurate in relation to the position of the piston. None of this solves Mike's crossover switch problem, but I'm trying to fully understand the reason he needs/wants the switch
The crank trigger allows for a more stable timing. If using the mag the amount of timing is unpredictable and can move all over the place because of gear slop or wear or anything. You can pretty well estimate that one degree of timing is worth about a 100 horsepower but that could be a plus or minus horsepower or move one degree advanced the one degree retard for a total change of two degrees. That can be a change of two hundred horsepower. If you are pushing traction to the limit then this can totally mess up your tune. So you want to be on the crank trigger for the run but that doesn't help you if the motor doesn't start on the crank trigger. You want the best of both worlds and start in on the mag and after it starts switch over to the crank trigger. The other way to do it is always start it and run it on the crank trigger and if it fails to fire on start then switch to the mag and get the motor started and then switch back to the crank trigger. The only way you can do all this is to have a crossover switch and there lays the problem, a switch that the contacts may or may not bounce and cause a misfire in the motor which will slow you down as what happened to us last weekend.
You could try here ..... http://www.itwswitches.com/Mil_Aero.shtml#
Just a thought Mike, but would it not work to have both triggers plugged in, in parallel to start the engine and then simply unplug the mag head plug while it is running? The signals should be very close and if a second one collapsed the field a second time a nano later, so what, the rotor position is still pointed at the same plug lead.
So no switch at all, just parallel leads. Jeff J.
Good idea but the rotor is not phased right on in the mag to help when the ignition is retarded. This would result in double trigger pulse.
Of course you know your mag setup and phasing but if it would be off enough to be a problem, the mag could be put in any position for starting only, correctly phased and the crank trigger placed for running only, correctly phased for your advance/retard swing. Even if it would get a double signal to the coil, the ignition would only collapse twice and think it was running at twice the speed and the rotor can only deliver spark to the post it is aimed at. And so what if it even gave the plug a double spark while it is sitting there idling? It would only be a spark into an already lit cylinder. The Nitro cars used to run both mags a bit out of phase and do exactly this and under power I believe.
You guys all know way more about this than me. But I don't get why you guys just don't run a blower starter, it would save you weight, and as yuo guys run outlaw stuff there is no need for the onboard starter. I never had a no start on my 48 volt blower starter. i don't even have a crossover switch. so less stuff to fail and maintain.
Hi Sune, the classes and associations we want to run with this year only allows onboard starters. The extra weight of the onboard starter actually helps us get up to the required weight.
Ahh ok my mistake. i thought you guys only ran outlaw stuff.