Philip Posted December 29, 2018 Report Share Posted December 29, 2018 Hello All, '75 M20F I have a PRESTOLITE ALY8420 alternator that I believe has gone bad. I get about 13.6+- volts when at cruise setting but it can drop a little lower at idle. Lately I have had the voltage enunciator flashing from time to time. Today I did some test and found 10.5 volts on the field wire at the alternator, my voltage regulator has a troubleshooting light on it and it's Green (a ok). I also tested the ohm's reading of the field on the alternator and got 9-15ohms spiking to 30+ ohms if I found the right spot while turning the pulley. This has led me to conclude I need a new alternator. I have contact AirPower in Arlington, TX and they only have a reman alternator ALY8520 supplied from Cessna. I want a new PlanePower alternator if I can get it. Where can I get a new alternator? Philip Quote Link to comment Share on other sites More sharing options...
FloridaMan Posted December 29, 2018 Report Share Posted December 29, 2018 Check the wires on the alternator. If your wires are old, I suggest replacing ALL of them, at least to the firewall, and not just repairing the connectors. They will fail again and leave you stranded somewhere when it will cost you a lot more money and be much more inconvenient. Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 29, 2018 Report Share Posted December 29, 2018 For the record, what VR do you have? Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Philip Posted December 29, 2018 Author Report Share Posted December 29, 2018 26 minutes ago, carusoam said: For the record, what VR do you have? Best regards, -a- ZEFTRONICS 1 Quote Link to comment Share on other sites More sharing options...
David Lloyd Posted December 29, 2018 Report Share Posted December 29, 2018 When you are checking resistance and seeing more than 6 ohms you most likely have worn brushes. Take your alternator to a local shop and have them check it for you. New brushes and bearings for your airboat alternator should be about $50. 1 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted December 29, 2018 Report Share Posted December 29, 2018 The brushes are about $20. You can change them without removing the alternator from the plane. Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted December 29, 2018 Report Share Posted December 29, 2018 Or you can get a new Planepower alt from Spruce. I got one from them about a month ago. Maybe $550. Probably coulda had the brushes changed for my “airboat” but I like new vs 50ish year old and my IA won’t play that game. 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted December 29, 2018 Report Share Posted December 29, 2018 Certified brushes for your alternator are less than $25.00. Any maintainer should be able to check/ replace them without removing the alternator. Clarence Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted December 29, 2018 Report Share Posted December 29, 2018 8 hours ago, Ragsf15e said: Or you can get a new Planepower alt from Spruce. I got one from them about a month ago. Maybe $550. Probably coulda had the brushes changed for my “airboat” but I like new vs 50ish year old and my IA won’t play that game. My wife is the same way. She says “I want a new wash machine” and I ask: “Is there something wrong with the washing machine?” And she says it works fine, but it is old and I want a new one. It makes me wonder what she thinks about me? 2 1 Quote Link to comment Share on other sites More sharing options...
FloridaMan Posted December 29, 2018 Report Share Posted December 29, 2018 29 minutes ago, N201MKTurbo said: My wife is the same way. She says “I want a new wash machine” and I ask: “Is there something wrong with the washing machine?” And she says it works fine, but it is old and I want a new one. It makes me wonder what she thinks about me? Pre-EPA washing machines are best washing machines. Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted December 29, 2018 Report Share Posted December 29, 2018 5 minutes ago, Antares said: Pre-EPA washing machines are best washing machines. The guy at the appliance parts store and some of the customers tell me the washer I have is the best one ever made and I should keep it going forever. That’s my plan. My wife says she loves me because I can fix anything. She also says she hates me because she never gets new things. 2 Quote Link to comment Share on other sites More sharing options...
Philip Posted December 29, 2018 Author Report Share Posted December 29, 2018 10 hours ago, Ragsf15e said: Or you can get a new Planepower alt from Spruce. I got one from them about a month ago. Maybe $550. Probably coulda had the brushes changed for my “airboat” but I like new vs 50ish year old and my IA won’t play that game. I have been searching but can't seem to understand which PlanePower model is correct for my '75 M20F with a IO-360-A1A. Can anyone help? Quote Link to comment Share on other sites More sharing options...
Philip Posted December 29, 2018 Author Report Share Posted December 29, 2018 Ok - as long as I need an alternator, I would like to upgrade while I'm at it and believe the Plane Power AL12-P70 is the correct fit for my 75 M20F. Can anyone confirm before I order one? Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted December 29, 2018 Report Share Posted December 29, 2018 Huh, you insist on replacing a perfectly good alternator instead of changing a normal wear item. The plane power alternator has brushes too. Wouldn't you rather spend your money on avgas? Quote Link to comment Share on other sites More sharing options...
David Lloyd Posted December 29, 2018 Report Share Posted December 29, 2018 Just before Interav sold out, I bought a brand new alternator from them to replace one with about 2500 hours. About 50 hours after installation the new one quit alternating. Problem? The brush assembly had been installed at an angle, only 1/2 of each brush was contacting the slip rings, and the brushes were worn at about a 30 degree angle until they no longer had adequate contact on the slip ring. So much for the new is better theory. Got a picture somewhere, will post if I find. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted December 29, 2018 Report Share Posted December 29, 2018 5 hours ago, Antares said: Pre-EPA washing machines are best washing machines. Can you explain this? Quote Link to comment Share on other sites More sharing options...
jetdriven Posted December 29, 2018 Report Share Posted December 29, 2018 4 hours ago, Philip said: Ok - as long as I need an alternator, I would like to upgrade while I'm at it and believe the Plane Power AL12-P70 is the correct fit for my 75 M20F. Can anyone confirm before I order one? That’s the one for the M20J. It replaces the 12v prestolite. But seriously replace the field wire from the firewall cannon plug to the alternator. Ours was acting up but the alternator was fine. So was the VR. The center conductor was shorting to the shielding. Kills the field and stops charging. Cost us 5$. Quote Link to comment Share on other sites More sharing options...
Yetti Posted December 29, 2018 Report Share Posted December 29, 2018 6 hours ago, Philip said: Ok - as long as I need an alternator, I would like to upgrade while I'm at it and believe the Plane Power AL12-P70 is the correct fit for my 75 M20F. Can anyone confirm before I order one? Call the manufacturer to confirm or use the TDS or STC Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted December 29, 2018 Report Share Posted December 29, 2018 AL12-P70 is correct. Ref: https://m.aircraftspruce.com/catalog/pdf/plane-power-pma2013.pdf Ok, generally I agree with all you guys about fixing stuff. Brushes probably easy enough, but there’s something to be said about starting fresh too. Maybe don’t tell your wife that-she May think you’re talking about more than the washing machine! Quote Link to comment Share on other sites More sharing options...
Philip Posted December 29, 2018 Author Report Share Posted December 29, 2018 Thanks for all your help guys! We pulled the brushes today and they were worn down to nothing. I have decided the easy and cheap fix is to replace the brushes. They are ordered and should be here soon. Thanks again. 3 Quote Link to comment Share on other sites More sharing options...
Guest Posted December 30, 2018 Report Share Posted December 30, 2018 35 minutes ago, Philip said: Thanks for all your help guys! We pulled the brushes today and they were worn down to nothing. I have decided the easy and cheap fix is to replace the brushes. They are ordered and should be here soon. Thanks again. A straight forward repair. As others have pointed out, old field wires are a common failure item as well. Clarence Quote Link to comment Share on other sites More sharing options...
RLCarter Posted December 30, 2018 Report Share Posted December 30, 2018 Is it common practice to turn the commutator when replacing the brushes if it is needed? 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted December 30, 2018 Report Share Posted December 30, 2018 Commutators are in starters and generators. Alternators have smooth copper slip rings, generally no need to turn them other than if the brush spring has made contact and scored the ring. Clarence Quote Link to comment Share on other sites More sharing options...
bradp Posted December 30, 2018 Report Share Posted December 30, 2018 On 12/29/2018 at 8:08 AM, N201MKTurbo said: My wife is the same way. She says “I want a new wash machine” and I ask: “Is there something wrong with the washing machine?” And she says it works fine, but it is old and I want a new one. It makes me wonder what she thinks about me? Same thing today I want a new dishwasher what’s the matter with the old one - the heater element went bad. New heater element on the way. The dishwasher will live to see another day. 2 Quote Link to comment Share on other sites More sharing options...
FloridaMan Posted December 30, 2018 Report Share Posted December 30, 2018 On 12/29/2018 at 1:52 PM, jetdriven said: Can you explain this? https://www.ar15.com/forums/General/-ARCHIVED-THREAD-So-the-EPA-has-ruined-washing-machines-too-/5-2051583/?page=2 Quote Link to comment Share on other sites More sharing options...
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