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07-18-2017, 01:50 PM
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Join Date: Jun 2016
Location: Houston, Tx
Posts: 40
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Mag check
Relatively new owner of a bought -7A. Recently, the left mag shows zero RPM drop during mag check. Could this be an issue? Appreciate any feedback!
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07-18-2017, 01:53 PM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,627
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Zero RPM drop could be an indication that the P-lead is broken or the switch is not working properly.
A quick check is to see if the engine will turn off at idle by using the switch. That will verify that the P-lead is good if it turns off. If it stays running then check the P-Lead.
If it does turn off, then I would suspect the switch.
Vic
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 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
Kitplanes "Unairworthy" monthly feature
EAA Sport Aviation "Checkpoints" column
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Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
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07-18-2017, 02:00 PM
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Join Date: Jan 2007
Location: Battleground
Posts: 4,348
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Be careful. That Mag could be HOT !
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Smart People do Stupid things all the time. I know, I've seen me do'em.
RV6 - Builder/Flying
Bucker Jungmann
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.
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07-18-2017, 02:23 PM
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Join Date: Sep 2007
Location: Hudson County, NJ
Posts: 1,092
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I'm no expert but you reminded me of my own experience. MY mags were barely dropping during run-up. I had bought the plane as well and after getting some "issues" worked out, it turns out she really needed some attention. At any rate, my mechanic rebuilt the mags and they were way off on timing (among other issues I think). They have been very consistent at around 50 rpm drop now after almost 400 hours.
It seems like you are in need of a rebuild (re-timing at a minimum) or you are running on one mag. Either one should get some quick attention I would think.
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07-18-2017, 02:33 PM
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Join Date: Jan 2017
Location: Alameda, CA
Posts: 29
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Lean the engine so that you can just get it to 1700rpm, then try the mag check. This will cause a much more significant drop in rpm on the mag check (if the mag is working).
If you still get no drop then, as others have said, you likely have a broken p lead and should be very careful as you have a hot mag.
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Dan Ainge
RV-7A N375M
2019 =VAF= dues paid
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07-18-2017, 02:59 PM
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Join Date: Jun 2016
Location: Houston, Tx
Posts: 40
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Thanks so much for your responses. Thought I might have been asking a dumb question, but looks like I might have a serious safety problem.
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07-18-2017, 03:33 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,687
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If you have an electronic ignition on the left 0 drop is normal.
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Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
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RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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07-18-2017, 03:36 PM
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Join Date: Jan 2007
Location: Battleground
Posts: 4,348
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If last time you flew and things where fine, and then all of a sudden they are not, my guess is a broken P-lead, usually the terminal. Do Vic's test. Of course this is all assuming standard mags.
If you do find it is a broken terminal, here is a thread that may help avoid this in the future.
http://www.vansairforce.com/communit...ailed+terminal
__________________
Smart People do Stupid things all the time. I know, I've seen me do'em.
RV6 - Builder/Flying
Bucker Jungmann
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.
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