hnorber

M20J Mag Timing Adjustment; Static RPM

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Quick question for group.   I was recently informed by SAVVY Analysis that my engine monitor data indicated that I have split mag timing.  I called a maintenance shop to ask about an adjustment, and they told me that for a dual drive mag (I have a Lycoming IO-360 A3BD6) that the mag actually needs to be removed and  opened up by a certified mag repair shop (which this shop  is) in order to adjust the timing.   Is that correct?  (I'm confused since my engine log shows that the mag timing was checked (and adjusted) at several annuals without the mag being sent out to a certified repair shop).  

Thanks in advance for any replies!
 

 

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I do it myself. I have the procedure. I don’t know why they would say it has to be done by a repair station.

I was flying to Dallas a while back and one of my mags quit. I stopped in Odessa and a repair shop reset the points and internal timing in a little over an hour. They only charged me $125. I was very pleased.

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The only thing that can cause a timing difference is unequal point gap. 

You have to take the cap off of the mag to remove it. At that point you have unrestricted access to the points. There is nothing else to open. 

I think your mechanic either doesn’t know how to do it or doesn’t want to.

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Thanks.   My mechanic told me that he has checked the timing at every annual - but I was calling a new shop (since my regular mechanic works out of his hangar, and it can be difficult to get his attention).  The shop that I called told me that the adjustment requires them to take out the mag and must be done by a certified repair shop (which they are) - but also told me that it will only take one hour.

 

 

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If it can be avoided, have your mechanic set the timing without pulling it. Pulling the mag involves new lock washers, torquing the nuts holding it down, etc. and generates more work than is really necessary. As @N201MKTurbo says above, not a really long job.

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Here is a Lycoming S/I calling for an improved hold down clamp for the D3000 series magneto.  It’s worth looking at your clamps to see which style you have.

Clarence

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Thanks.  I think that the clamp was replaced to comply with the SI, but we'll triple check.  I'm curious as to why the service manager is telling me that the mag needs to come off?  (It's a very reputable shop - they also have an engine shop on-site).   I'm pretty sure he wasn't thinking about internal timing, because I explained that my Savvy analysis indicated split mag timing.  Sounds like plenty of folks are able to adjust the timing (external - to engine) on an M20J with a D engine without removing the mag.

 

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Personally I would remove the mag to re set the points, but that’s only me. I find it’s easier to get the timing exactly the same on the bench.  It doesn’t really take too long to remove and reinstall the mag and set the timing to the engine.

Clarence

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You have to remove the magneto to put in the newest style hold-down clamps as well.

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On 8/4/2019 at 8:32 AM, hnorber said:

Quick question for group.   I was recently informed by SAVVY Analysis that my engine monitor data indicated that I have split mag timing.  I called a maintenance shop to ask about an adjustment, and they told me that for a dual drive mag (I have a Lycoming IO-360 A3BD6) that the mag actually needs to be removed and  opened up by a certified mag repair shop (which this shop  is) in order to adjust the timing.   Is that correct?  (I'm confused since my engine log shows that the mag timing was checked (and adjusted) at several annuals without the mag being sent out to a certified repair shop).  

Thanks in advance for any replies!
 

 

I'd say skip that shop, sounds like they want $$.  Shouldn't be more than a usual timing bump. Unless it's been bumped a bunch and needs an inspection.

Edited by jkarch

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As a follow-up, I took the plane to the shop for the timing adjustment yesterday.  They made the adjustment without removing the mag - but what they explained was that they would need to remove the mag in order to reduce the split - but they could move the timing on both mags in sync without removing.  Essentially - my split was 1 degree (which, they told me is within permitted tolerances) - and was firing early at 27.5 and 28.5 degrees, respectively.   They moved the timing to 24.5 and 25.5 (therefore within a half degree of book timing) - but that they would need to remove the mag to adjust them separately and eliminate the split (so that they would both fire at 25 degrees BTDC).

I don't understand why the split can't be eliminated without removing the mag - but certainly they weren't trying to squeeze me for more $, since they told me that the 0.5 degree discrepancy was fine and that there was no need to remove the mag.

 

Separately, I asked them to inspect my cylinders since my oil consumption has increased significantly recently (probably about a quart every 2.5 hours now).  They showed me that all 4 cylinders were glazed and that I need a full Top Overhaul (quoted me btwn $5K and $8K to overhaul my existing cylinders - I think that the higher end of the range would be for replacing the pistons, if necessary).  I currently have 1950 hours on the engine - so I'm inclined to overhaul they cylinders rather than replace them with new ones.

Happy to listen to any thoughts/suggestions regarding the Top Overhaul.  I understand that it's unwise to replace all 4 cylinders where the diagnosis is only one or two bad cylinders, but here it looks like all 4 legitimately need to be overhauled. 

 I plan to start a new topic on this as well (so that it won't fall under the label 'mag timing') .

 

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How many hours are on your magneto? If it is over 500, you should remove it and send it Select Aircraft in Lancaster, TX for a 500 hour service. I don't think I'd tolerate the split timing...something is worn and you shouldn't mess around with the dual mag. It needs some expert attention IMO.

Sent from my LG-US996 using Tapatalk

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1 hour ago, hnorber said:

As a follow-up, I took the plane to the shop for the timing adjustment yesterday.  They made the adjustment without removing the mag - but what they explained was that they would need to remove the mag in order to reduce the split - but they could move the timing on both mags in sync without removing.  Essentially - my split was 1 degree (which, they told me is within permitted tolerances) - and was firing early at 27.5 and 28.5 degrees, respectively.   They moved the timing to 24.5 and 25.5 (therefore within a half degree of book timing) - but that they would need to remove the mag to adjust them separately and eliminate the split (so that they would both fire at 25 degrees BTDC).

I don't understand why the split can't be eliminated without removing the mag - but certainly they weren't trying to squeeze me for more $, since they told me that the 0.5 degree discrepancy was fine and that there was no need to remove the mag.

 

Separately, I asked them to inspect my cylinders since my oil consumption has increased significantly recently (probably about a quart every 2.5 hours now).  They showed me that all 4 cylinders were glazed and that I need a full Top Overhaul (quoted me btwn $5K and $8K to overhaul my existing cylinders - I think that the higher end of the range would be for replacing the pistons, if necessary).  I currently have 1950 hours on the engine - so I'm inclined to overhaul they cylinders rather than replace them with new ones.

Happy to listen to any thoughts/suggestions regarding the Top Overhaul.  I understand that it's unwise to replace all 4 cylinders where the diagnosis is only one or two bad cylinders, but here it looks like all 4 legitimately need to be overhauled. 

 I plan to start a new topic on this as well (so that it won't fall under the label 'mag timing') .

 

You can re-ring and hone the cylinders for a lot less than that.

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1 hour ago, KSMooniac said:

How many hours are on your magneto? If it is over 500, you should remove it and send it Select Aircraft in Lancaster, TX for a 500 hour service. I don't think I'd tolerate the split timing...something is worn and you shouldn't mess around with the dual mag. It needs some expert attention IMO.

Sent from my LG-US996 using Tapatalk
 

Thanks.  Mag has 300 hours since last overhaul.

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To see the effects of the split timing...

Use an engine monitor... post graphs using Savvy....

You will see a difference in EGTs from Rmag to Lmag... during the run-up...

Got an engine monitor?

Best regards,

-a-

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Mag trying to tell you something.  Send it to Aaron in Lancaster TX.  You’ll be glad you did.  He does fantastic work.  

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47 minutes ago, bradp said:

Mag trying to tell you something.  Send it to Aaron in Lancaster TX.  You’ll be glad you did.  He does fantastic work.  

Aaron Williams is Select Aircraft Services. Super knowledgeable and a nice guy as well.

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I havent personally used them, but they are reputed to be THE D2000/D3000 mag shop.  @cnoe can tell you.

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I had so many issues with a 4300 series slick mag.  First IRAN I had I asked shop to send to Aaron, but they didn’t.  Instead they sent to the shop of their choice (this is the same MSC that another user posted about getting bilked on ICAs and a shady deal with their attached avionics shop... hint it’s the only one in VA).  Anyway that mag shop in Florida sent me back a mag with a bad secondary not once but twice with a bunch of AOGs for me and much frustration on my part.  Third try they sent me a  Frankenstein mag with a bunch of parts they had.  This one worked for ~250hrs before the points went out.  

This time I’m no slouch, so I RRd myself and sent to Aaron at Select in Lancaster (TX).  He’s totally knowledgeable, reasonable, fair and honest.  Couldn’t ask for better work.  Good guy and talented with ignitions.  Turn around time was about a week and a half. 

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I have a couple of questions for the experts on ignition timing. (a)  Is it correct that an advanced timing (such as 25 deg compared to 20 deg) make the plane harder to start when cold?  The timing on my A3B6 two drive magneto has wandered off a bit to the 25 or 27 deg mark. I don't have much of a problem starting hot, but when cold, it requires at least 2 or 3 sets of cranks. (b) How does the RPM drop change when operating on one mag (either L or R). I notice that the RPM drop is now around 100 or so (used to be 40 or so when the timing was correct). I have the Slick magnetos and coming up on the 500hr and will probably replace the L mag with the Surefly to getter starting performance and the variable timing. Thanks.

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It depends on the retard breaker setting or the impulse coupling. They should fire it at TDC. If either is set for 20 degrees and you set your mag to 25 degrees then it will fire at -5 instead of TDC. This will make it harder to start.

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So...

if the mags are set up properly, the regular timing doesn’t matter.  The start timing is 0° at Top Dead Center... for all Mooney engines.

This keeps Most starts from occuring in reverse...

In the odd case of the engine firing before TDC... the starter ring can get beat up... while fighting the starter...

Probably not good for the starter either...

PP thoughts only, not a mechanic ...

Best regards,

-a-

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Observation: some owners complain that their mechanic is too picky (expensive) others feel their mechanic isn’t thorough enough. The FAA gives mechanics a lot of leeway to use good judgement to determine what is airworthy and it’s not all black and white, so find a mechanic that has standards that match yours an you’ll both be happier. 

Skip

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