Posted: Thu Jan 20, 2011 6:29 am
Original Posted By: Ben Charvet
Listers,Here is a copy of an email I just sent to Larry Morlock detailing my 2nd mag drive troubles, after he inquired about it. Hi Larry,I had 13 hours on her (in flight). Maybe another 10 on the ground. During the flight the trouble occurred, I had checked the mags (in flight) individually before I left the proximity of the airport. All seemed well so I ventured out. The engine started running rough, and I checked the mags to discover that the cam gear-driven mag appeared to be completely dead. As of this date, I am still unsure why the engine continued running rough after I shut off that mag, and switched over to the crank mag. That is still a mystery to me. The only thing I can think of, is that in my panic, maybe I left the switch on "both" and the cam-driven mag was catching periodically (because of the partial tooth situation) and it was sending wild sparks in there.So I am not quite sure even now what happened, or exactly when. As you can see from the photos about 30% of the gear teeth are completely cracked off. The remaining teeth appear to be "worn" off. This is my speculation: There was insufficient clearance between the aluminum timing gear and the steel magneto gear. I had no trouble inserting and mounting that magneto at all, so no red flags were raised at that time. In my ignorance, I did not check the clearance between the gears. Over a period of hours, pressure was exerted onto the aluminum gear teeth and the metal failed on a number of the teeth, either from fatigue, or just the continued "mooshing" of the steel mag gear teeth against the aluminum teeth.When I contacted Ken Perkins, he speculated the same, and said the fix was adding shims (or extra gasket thickness) between the mag housing (casting that the mag is bolted to) and the engine block to achieve a clearance of four thousandths. This action would necessarily give more clearance between the two gears in question. But upon further examination, this action creates another problem. It is kind of hard to explain in an email, but there are three bolt holes that would have to be elongated, in the flat timing gear cover, in order to allow those three timing gear cover bolts to line up with the holes in the back of the engine block. I guess this would not be that big of a deal because only a few thousands of an inch would be needed. I myself have decided to go in another direction as far as the 2nd (redundant) ignition system goes (mostly to satisfy my wife). The Model A car suppliers sell an electronic ignition module that drops into a traditional distributor body. It will appear to be a stock Model A ignition system. Downside for me, is that I need a battery. I found a light weight battery at Wicks (4.4 lbs) that I will use. Another hang up is how is it recharged? I will maybe get a solar cell to put out when I am on the ground. Who knows, after you have proven the viability of the Perkins mag drive, I might go back to that! BTW Falluca told me that the aluminum gear should have had no problem with this set-up if clearances were correct.I think you would be wise to, during your on-ground break-in period, periodically remove that mag and peer in there to closely inspect that gear to see how it is doing. BTW, there was no apparent wear or damage that I can detect on the steel mag gear.I am willing to send you this aluminum gear for your close inspection. You may be able to glean some clues upon close examination. Let me know and I will UPS or mail it over to you.Please ask me more specific questions if you have them, and I will be more than glad to help however I can. Dan________________________________________________________________________________Date: Thu, 20 Jan 2011 08:26:35 -0500
Listers,Here is a copy of an email I just sent to Larry Morlock detailing my 2nd mag drive troubles, after he inquired about it. Hi Larry,I had 13 hours on her (in flight). Maybe another 10 on the ground. During the flight the trouble occurred, I had checked the mags (in flight) individually before I left the proximity of the airport. All seemed well so I ventured out. The engine started running rough, and I checked the mags to discover that the cam gear-driven mag appeared to be completely dead. As of this date, I am still unsure why the engine continued running rough after I shut off that mag, and switched over to the crank mag. That is still a mystery to me. The only thing I can think of, is that in my panic, maybe I left the switch on "both" and the cam-driven mag was catching periodically (because of the partial tooth situation) and it was sending wild sparks in there.So I am not quite sure even now what happened, or exactly when. As you can see from the photos about 30% of the gear teeth are completely cracked off. The remaining teeth appear to be "worn" off. This is my speculation: There was insufficient clearance between the aluminum timing gear and the steel magneto gear. I had no trouble inserting and mounting that magneto at all, so no red flags were raised at that time. In my ignorance, I did not check the clearance between the gears. Over a period of hours, pressure was exerted onto the aluminum gear teeth and the metal failed on a number of the teeth, either from fatigue, or just the continued "mooshing" of the steel mag gear teeth against the aluminum teeth.When I contacted Ken Perkins, he speculated the same, and said the fix was adding shims (or extra gasket thickness) between the mag housing (casting that the mag is bolted to) and the engine block to achieve a clearance of four thousandths. This action would necessarily give more clearance between the two gears in question. But upon further examination, this action creates another problem. It is kind of hard to explain in an email, but there are three bolt holes that would have to be elongated, in the flat timing gear cover, in order to allow those three timing gear cover bolts to line up with the holes in the back of the engine block. I guess this would not be that big of a deal because only a few thousands of an inch would be needed. I myself have decided to go in another direction as far as the 2nd (redundant) ignition system goes (mostly to satisfy my wife). The Model A car suppliers sell an electronic ignition module that drops into a traditional distributor body. It will appear to be a stock Model A ignition system. Downside for me, is that I need a battery. I found a light weight battery at Wicks (4.4 lbs) that I will use. Another hang up is how is it recharged? I will maybe get a solar cell to put out when I am on the ground. Who knows, after you have proven the viability of the Perkins mag drive, I might go back to that! BTW Falluca told me that the aluminum gear should have had no problem with this set-up if clearances were correct.I think you would be wise to, during your on-ground break-in period, periodically remove that mag and peer in there to closely inspect that gear to see how it is doing. BTW, there was no apparent wear or damage that I can detect on the steel mag gear.I am willing to send you this aluminum gear for your close inspection. You may be able to glean some clues upon close examination. Let me know and I will UPS or mail it over to you.Please ask me more specific questions if you have them, and I will be more than glad to help however I can. Dan________________________________________________________________________________Date: Thu, 20 Jan 2011 08:26:35 -0500