Mag timing procedure with 25 deg impulse coupling?

[FlyBoyM20J]

It's annual time and I have the chance to participate in the work this year.  Great experience for me.  I do want to get my A&P someday.

I have been authorized by my IA to perform the replacement of long overdue vacuum pump and OH'd dual magneto after which he will inspect and so forth. 

At this point, I have the pump and the mag installed after a few hours of figuring out how not to do things in the wrong order (put the fittings on the vacuum pump before you install it, and so forth), but I am not certain of the timing procedure for the dual magneto.

It's a Bendix 10-682555-11 (D4LN-3000) with a 25-degree impulse coupling. 

Is this the general idea?

1) Set crank to 25 deg prior to TDC for C1

2) Set magneto to K minus a bit to magnetic neutral

3) Attach mag to accessory port and finger-tighten clamps

4) Attach timing lights to P-terms (I have adapters)

5) Rotate prop slowly through a few cycles to ensure impulse coupling is engaged

6) Expect points to open at TDC for C1, not 25 deg prior?

How do I precisely adjust timing?  I'm not sure how rotating the magneto a few degrees to fine-tune will work with the impulse coupling there.  But there is some play in the magneto position relative to K when back-rotated to magnetic neutral, and some play in how the mag drive gear meshes with the crank idler, so it seems that some fine-tuning is required.

Cliff

[EricJ]

On most Bendix mags there's a plug you can remove to see the plastic drive gear, and there's a red tooth on the gear.   When that red tooth is visible the rotor is pointing at the #1 lead.   Install the mag when it is in this position and the #1 cyl is at the desired timing location (e.g., 25 degrees BTDC on the compression stroke).   When the mag is installed it can then be turned slightly so that the points open at the desired crank angle, as shown with a timing light connected to the p-lead.   With a dual mag there is a spec of a couple of degrees for the points to open relative to each other.

The main consideration with the impulse coupler is that you move the prop to get it to trip before you set the timing.   You do that by ear, i.e., listen for it to trip, then move the prop back to where it needs to be and then set timing moving the prop forward slowly.

There are a bunch of vids on YT and elsewhere online showing how to set timing on typical GA aircraft engines.   A nice thing on an M20J is that you can use the marks on the flywheel gear teeth to set the crank position pretty easily.   Just make sure it's on the compression stroke, which can be verified by removing a plug on the #1 cyl and put your thumb on it when moving the prop.  

This is a simple enough process that if your IA is willing to supervise your work it doesn't take very long for them to show you the basics of how to do it.

Edited July 6, 2020 by EricJ

[kortopates]

No, you pull the prop through just enough so the impulse coupling fires. Then pull the prop back to before 25 BTDC and set the mag to engine timing to your 25 degrees.

 

[FlyBoyM20J]

6 minutes ago, kortopates said:

No, you pull the prop through just enough so the impulse coupling fires. Then pull the prop back to before 25 BTDC and set the mag to engine timing to your 25 degrees.

 

OK, this makes sense.  Thanks!

[Guest]

Be sure to use the new style clamps as called out in SI1508C.  Use the correct gasket and use new lock washers, torque the nuts to 204”LBS

The accuracy of getting both magnetos to fire at 25 degrees, depends on how closely both points were set when the internal timing was set.

Clarence

Edited July 6, 2020 by M20Doc

[FlyBoyM20J]

56 minutes ago, M20Doc said:

Be sure to use the new style clamps as called out in SI1508C.  Use the correct gasket and use new lock washers, torque the nuts to 204”LBS

The accuracy of getting both magnetos to fire at 25 degrees, depends on how closely both points were set when the internal timing was set.

Clarence

I have the new style clamps per the Si for mounting dual mags.  Lucky there, I guess.  QAA sent a new gasket and I torqued both nuts to 17 ft lbs (204 in. lbs).

Before I torqued down, I had finger-tight and verified by my timing light that the points open right at 25 deg BTDC for C1 and that the red line on the distributor gear was visible in the side port of the mag at that point.  All looked good.  Both left and right points open within a fraction of a degree of each other, as far as I can tell.  Right is first. 

But when I tried to run the engine just now, it did not start.  Cranks fine, just no start.

I didn't try for long.  Been a long day in the hangar so I packed things back up and will consider this further from home.

BTW: It seems to me when I pull the prop through to trip the impulse coupler that the impulse retard is beyond TDC.  Maybe this is how it seems when hand-pulling, but if the impulse coupled retard is past TDC, that would account for no start, I suppose.  I don't want to assume QAA did a bad overhaul.  This must be something I have done wrong.

Cliff

[carusoam]

Somewhere there is probably advice on how to log your time working on the mechanical things...

If you are going for an A&P license, I believe there is a time requirement...

If this counts, might as well start collecting in it in a proper fashion...

Thanks to all the A&Ps that add their experience around MS...

PP thoughts only, not a mechanic...

Best regards,

-a-

[FlyBoyM20J]

Just now, carusoam said:

Somewhere there is probably advice on how to log your time working on the mechanical things...

If you are going for an A&P license, I believe there is a time requirement...

If this counts, might as well start collecting in it in a proper fashion...

Thanks to all the A&Ps that add their experience around MS...

PP thoughts only, not a mechanic...

Best regards,

-a-

My IA has delegated other work on other planes to me and says I do excellent work (mostly tracking down electrical gremlins), and he knows I want to get my A&P.  His question for me was "why don't you get your A&P?  You should!"  I said time was the issue.  I'm sure he'll help me log time if that's the way.  I'll talk with him when he gets back on the field in a day or 2. 

But I've read on here that it can take years doing it at this rate.  I guess that's OK. 

Cliff

 

[N201MKTurbo]

Double check that the red tooth Is in the hole with #1 at TDC on the compression stroke. I wish I could say that I’ve never put a mag on 180 out, but I can’t. That’s always been the problem.

[FlyBoyM20J]

1 hour ago, N201MKTurbo said:

Double check that the red tooth Is in the hole with #1 at TDC on the compression stroke. I wish I could say that I’ve never put a mag on 180 out, but I can’t. That’s always been the problem.

This may be it!

The manual for this mag (the D4LN-3000) says to init the phase of the mag by rotating in the normal rotation direction until 'K' is found in the top view and the red marks are on the gear teeth visible in the side ports.  I did that and there is a bit of red paint near the 'K' that is centered when the points open.  That's what is centered when the prop is at 25 BTDC on C1 now that the mag is installed.  I pulled the top plugs and verified timing after I failed to get the engine to catch.

But, now that you mention it, I realize that I must have initially found 'K' by rotating the mag drive backwards - that is, I was definitely not engaging the impulse coupling on the bench.

So, if it's possible to have found 'K' and the red marks be at side ports (and have all this stuff always come up at 25 BTDC for C1 after install) but having come at them by hand driving the mag in reverse, I guess I screwed up in precisely this way.

Easy fix tomorrow AM.  I'm getting good at removing, adjusting, and re-installing this mag.  I am not happy with how cramped it is back there and I have some banged up fingers and some words for whoever didn't trim the zip tie ends on all those bundles of wires.  But I'm getting better at this stuff.

Cliff

 

[FlyBoyM20J]

Update:  it works now.

I was overthinking it.  The timing was just late by a degree or 2.  Being timed for 24 degrees BTDC means that the +25 impulse coupling will fire 1 degree beyond TDC.  Not gonna start the engine that way.

I re-timed to exactly 25 BTDC and the engine started up and ran well.  I did a rich mag check and then a lean mag check. 

Thanks everyone for the help.

Cliff

[carusoam]

Cliff,

a really good run up with an engine monitor set up properly will show how good your Mag timing matches each other.

If you have a JPI... collect data, up load to savvy, click share, post link...

When doing a run-up wait a few extra seconds on each mag click... allow the temps to stabilize....

PP thoughts only, not a mechanic...

Best regards,

-a-

[FlyBoyM20J]

Here's the plot from my JPI set at 2-sec capture intervals.  I stayed roughly 30 seconds in each stage.  First full-rich run-up (Both, R, Both, L, Both) then lean run-up (same sequence).

We can see here that C4 is richest and C2 is leanest.  I already know that and am working on balancing that better.

I'm a bit disappointed in how much hotter the left mag is relative to the right in the lean runup.  The prior mag that had > 1000 hours on it had a similar profile.  I'll find some data and review it to see just how similar.  But the data below bears out the timing light signals: right mag fires a little before left mag.  By less than 1 degree as far as I was able to determine when setting timing earlier today. 

Perhaps C4 is just on the edge of LOP and the ~1-deg timing retard for left mag pushes it back up a steep slope?

Cliff

[carusoam]

Can you share the link?

The pic is pretty nice, but the data is really much more helpful.

When the timing is different between mags... their EGT peaks are different...

With access to savvy data... people can put a mark on the graph and ask... what’s this?  What caused that? That kind of thing...

or why does this mag check look so good... and EGT is all spread out on that mag...

Best regards,

-a-

[FlyBoyM20J]

Just now, carusoam said:

Can you share the link?

The pic is pretty nice, but the data is really much more helpful.

When the timing is different between mags... their EGT peaks are different...

Best regards,

-a-

I'll have to figure out how to upload to Savvy.  I never have done that - I just analyze it using EzTrends on my local computer and this is a screencap from that. 

I do find it interesting that C1 and C3 EGT peaks stay roughly the same for lean mag on both R and L mags.  But the spread between C2 (leanest) and C4 (richest) is increased when I switch to L mag in lean test.  If I'm correct in my bench and engine-mounted timing tests that R points open less than 1 degree prior to L points, this seems an rather severe consequence.

I suspect something else...perhaps leads on C4 and C2?  Or C4 spark plug?

Cliff

[carusoam]

Check to see what plugs you have...

If they say a Champion on them... check their resistance...

If they say other manufacturer on them check to see if they are whole, not missing any parts...

Loading data to savvy Is pretty easy... and free...

MSers do it often...

Best regards,

-a-

[FlyBoyM20J]

On 7/7/2020 at 2:58 PM, carusoam said:

Check to see what plugs you have...

If they say a Champion on them... check their resistance...

If they say other manufacturer on them check to see if they are whole, not missing any parts...

Loading data to savvy Is pretty easy... and free...

MSers do it often...

Best regards,

-a-

They're Champions.  The C4 plug on left mag is the lower plug.  I'll check it later today.

Cliff

[carusoam]

Comparing the two sets of peaks... is pretty easy.

If I have identified the mag tests properly, they aren’t looking alike as they usually do...

Right first, then left.... 

The right mag is showing a pretty mellow peak...

The left mag is showing two plugs in disagreement with each other...

Follow-up question...  what is going on with EGT4.  At the two minute mark, maybe as some leaning occurs.... it leaves the pack. As if there is less FF to the injector to that cylinder...
 

Something to look closer into...

Best regards,

-a-

[FlyBoyM20J]

Yes, those are the two lean tests.  The first, better-behaved one is the Right mag.  The second one in which C4 temp rises and C2 falls is the Left mag.

This is a brand-new overhauled mag by QAA.  I tried to reach Aaron at Select and he kindly wrote back telling me he had moved on, so I went with QAA.

I do hope the slight (~1 deg) advance of right points over left is not the whole story here.  I'm not sure how to get a better build on a mag and I believe that 1 deg is within spec.

But I already know I need to balance the fuel flow between cylinders better.  Replacing the mag was the first required step to this process since the old mag produced similar lean test profiles to this and also had far too many hours on it.  Unfortunately, I did not do a timing test on the old mag while it was still on the engine so I do not know for certain what the spread between R and L points is for it to the level of accuracy that I do the new mag.

Cliff

[carusoam]

If not familiar...

The baby food jar test...  four glass containers, identical in shape and size.... used to collect fuel samples from the four fuel lines over a period of time...

 with and without injectors on the lines...

You might find an oddity to fuel flow doing this test...

The test will ferret out flow issues from the fuel divider and/or blocked fuel injectors...

A great time to use Hopp’s #9 for injector cleaning...

PP thoughts only, not a mechanic...

Best regards,

-a-

[RLCarter]

20 hours ago, FlyBoyM20J said:

I was overthinking it.  The timing was just late by a degree or 2.  Being timed for 24 degrees BTDC means that the +25 impulse coupling will fire 1 degree beyond TDC.  Not gonna start the engine that way.

I re-timed to exactly 25 BTDC and the engine started up and ran well.  I did a rich mag check and then a lean mag check. 

I would be cautious, 1 or 2° would not keep it from starting or running. 

[FlyBoyM20J]

34 minutes ago, RLCarter said:

I would be cautious, 1 or 2° would not keep it from starting or running. 

Edit: just re-read your comment...well, 1 or 2 degrees might keep it from starting if we account for the +25 degrees contributed by the impulse coupling at startup, won't it?  If I had timed it to 23 or 24 degrees, then the impulse coupling would add 25 and we'd be 1 or 2 degrees on the other side of the compression stroke.

----

Yes, so I found.  I believe that I had not accounted for gear lash sufficiently when I back-turned the prop after the impulse coupling fired.

I re-timed it yesterday and was very, very careful and verified it multiple times and multiple ways.  R points open at perhaps 25.5 degrees and L open at 25 degrees.

It runs well now, thanks.

Cliff

 

[RLCarter]

If the impulse coupler was engaged when the timing was set your timing would be off by the lag time of the coupler (25° ish). I’ve always used a degree wheel on the prop and a positive stop to find TDC (compression stroke), and rotate the crankshaft far enough to have the coupler disengage (snap) then rotate the crank backwards to the proper timing mark. If you rotate the crank too far backwards the impulse coupler will re-engage screwing things up again. One way to check is once the mag(s) is timed continue rotating past the timing mark 30° or so and the coupler SHOULD NOT snap

[FlyBoyM20J]

8 minutes ago, RLCarter said:

If the impulse coupler was engaged when the timing was set your timing would be off by the lag time of the coupler (25° ish). I’ve always used a degree wheel on the prop and a positive stop to find TDC (compression stroke), and rotate the crankshaft far enough to have the coupler disengage (snap) then rotate the crank backwards to the proper timing mark. If you rotate the crank too far backwards the impulse coupler will re-engage screwing things up again. One way to check is once the mag(s) is timed continue rotating past the timing mark 30° or so and the coupler SHOULD NOT snap

Understood, and this is what I did the second time around.  I was tired on Monday when I first timed it.  I didn't try to crank much, just stopped for the day.

I went back yesterday (Tuesday) and carefully engaged the impulse coupler on the compression stroke of #1, turned prop just until it snapped, then carefully turned prop back to about 35 degrees.  Then forward to 25.5, timed mag for right points to open there and left points by 25.0 (as far as I could tell by a pointer at case seam against marks on flywheel).  So, both sets of points open by 25 degree mark on flywheel.  Not later. 

Verified several times with 2 different timing light boxes and then started engine.

It started right up and so I stopped, put cowls back on, and taxied it to the ramp for run-up testing.

I think I have a handle on this now, but please correct me if I'm mistaken. 

[RLCarter]

Sound like your good to go, I will throw in the @carusoam disclaimer that I’m not an A&P . I would of had my A&P verify the work before re-cowling it, my A&P gets annoyed at times when I have him check my work but I don’t care....lol