Mag Timing and Timed out.

[Steve Tadlock]

1968 Mooney M20 F,, IO360 A1A. Lots to unload here. Engine ID plate has 25 BTDC XXXed out and has 20 BTDC next to it. Ok, read some things about that and thats cool. Problem is looking at mags and they are dated from 2007 and show 15 BTDC. Cant find any where that that is a valid timing. Engine was missing, changed plugs, mag check looked great. Ran 10 min and started missing and mag check was awful, missing like it was missing on 2 cylinders. Right mag was issue, smoothed out on left or both. But switching to right it sucked. Obviously the mags are out of date, will have replaced. Just wondering about timing though. I think as the mag warms up its coil breaks down. Logs show last mag replacement was in 97, but date on current mags show 2007. No record of being replaced except in 97. Any way, just wanted to pick yalls brains. TIA

[PT20J]

The mags must be timed to the engine per the data plate. In your case, 20 deg BTDC.

Did you check the actual timing or are you inferring 15 deg because of the label on the mag? The lag angle is the angle that the mag fires during starting which must be closer to TDC than normal timing or the engine will kick back due to the slower rotation when driven by the starter. 15 deg is the correct lag angle for 20 deg BTDC engine to mag timing. Only the left mag should have a 15 deg lag angle; the right mag should have a 0 deg lag angle.

Mags should be serviced every 500 hrs. 

 

 

[LANCECASPER]

6 hours ago, Steve Tadlock said:

1968 Mooney M20 F,, IO360 A1A. Lots to unload here. Engine ID plate has 25 BTDC XXXed out and has 20 BTDC next to it. Ok, read some things about that and thats cool. Problem is looking at mags and they are dated from 2007 and show 15 BTDC. Cant find any where that that is a valid timing. Engine was missing, changed plugs, mag check looked great. Ran 10 min and started missing and mag check was awful, missing like it was missing on 2 cylinders. Right mag was issue, smoothed out on left or both. But switching to right it sucked. Obviously the mags are out of date, will have replaced. Just wondering about timing though. I think as the mag warms up its coil breaks down. Logs show last mag replacement was in 97, but date on current mags show 2007. No record of being replaced except in 97. Any way, just wanted to pick yalls brains. TIA

You mention replacing your mags. Most of the time having them serviced by someone that really knows mags is more cost effective. Even though I live in TX I have used Robert at Aero Accessories in Van Nuys CA. http://aeroacc-vny.com/ I ask him to do an IRAN (Inspect and Replace parts As Necessary). He has always done it very well and turned them around in a few days at a fair price. They come back like brand new. I would trust a mag that he has serviced more so than a new one out of the box. 

Also once you know you have good mags and the engine timed correctly by someone that does this often, then if it's still not running as well as you'd like you could check the resistance of your spark plugs. Many people, including myself, have had good results with Tempest Fine Wire plugs. Also you might check your wiring harness from the mags to the plugs. It could be fine but if it's been decades since it's been changed it may well be worth it. But I wouldn't do everything at once. I would try one step at a time so you can identify what's working and what's not. 

[Steve Tadlock]

7 hours ago, PT20J said:

The mags must be timed to the engine per the data plate. In your case, 20 deg BTDC.

Did you check the actual timing or are you inferring 15 deg because of the label on the mag? The lag angle is the angle that the mag fires during starting which must be closer to TDC than normal timing or the engine will kick back due to the slower rotation when driven by the starter. 15 deg is the correct lag angle for 20 deg BTDC engine to mag timing. Only the left mag should have a 15 deg lag angle; the right mag should have a 0 deg lag angle.

Mags should be serviced every 500 hrs. 

 

 

You read my post and answered every concern and yes you are so right. I did some more reading understand the lag timing and its purpose. Yes left mag shows the lag time. The mags should of been swapped years ago. If logs are correct they have 800+ hours on them. I just bought the plane, so still playing catchup on it being idle for many years. Paying the hangar tax right now. Slick, straight plane, virgin panel and usual issues with not being flown. The plate original stamped was 25 BTDC and they XXXed that out and stamped 20 on it. Waiting for A&P to get to it. Getting some cooler temps in W. Texas and getting antsy wanting to fly. KODO

Thanks

[Shadrach]

2 hours ago, Steve Tadlock said:

You read my post and answered every concern and yes you are so right. I did some more reading understand the lag timing and its purpose. Yes left mag shows the lag time. The mags should of been swapped years ago. If logs are correct they have 800+ hours on them. I just bought the plane, so still playing catchup on it being idle for many years. Paying the hangar tax right now. Slick, straight plane, virgin panel and usual issues with not being flown. The plate original stamped was 25 BTDC and they XXXed that out and stamped 20 on it. Waiting for A&P to get to it. Getting some cooler temps in W. Texas and getting antsy wanting to fly. KODO

Thanks

I’ll take an opportunities to add an unsolicited opinion. I think the angle valve IO360 runs better timed at 25° BTDC.  The benefits are more apparent at peak and lean of peak settings.

[Fly Boomer]

9 hours ago, Steve Tadlock said:

Any way, just wanted to pick yalls brains.

This article from Sacramento Sky Ranch has a description of lag specifications for impulse mags, which starters should be used with which lag, and what happens if you mismatch magneto lag and starter.

Magneto Ignition Systems.pdf

 

[Marc_B]

Another shop that does solid work is Aircraft Magneto Services in Montana.  https://www.aircraftmagnetoservice.net/

Easy to print out a prepaid mailer from their website, fill out a service order, and ship in.  They typically have their turn around times listed on the website.  They also have an AOG service for a quicker turn that adds a couple hundred but takes you to the front of the line.

[MooneyMitch]

4 hours ago, LANCECASPER said:

You mention replacing your mags. Most of the time having them serviced by someone that really knows mags is more cost effective. Even though I live in TX I have used Robert at Aero Accessories in Van Nuys CA. http://aeroacc-vny.com/ I ask him to do an IRAN (Inspect and Replace parts As Necessary). He has always done it very well and turned them around in a few days at a fair price. They come back like brand new. I would trust a mag that he has serviced more so than a new one out of the box. 

My experience a few years ago with Robert and the good folks at Aero Accesssoires....................and my opinion and suggestion................. during 500 hr IRAN, ask the shop to replace the condensers too!  I learned from Robert that the condensers are NOT part of the 500 hr part replacement.  They give them a visual only inspection.

How I learned this.................... recent 500 hr serviced Aero Accessories mags installed with approximately 30 hours of operation, right mag failed in flight.  Robert discovered the condenser had failed.