Jump to content

Need help diagnosing a starting problem


Recommended Posts

8 minutes ago, Ragsf15e said:

IF it does end up being the SOS, it may not cost much.  If it starts to add up though, a Surefly mag is an option as you no longer need the sos.  You can keep your newly oh spare mag on the shelf or sell it.

So I know basically nothing about electronic mags.  Would I replace just one (the left?) and leave my existing right mag?  Then I'd remove the SOS entirely?

Link to comment
Share on other sites


Matt,

The left mag is the specific mag for starting...

It has a specific extra set of points (a switch in a circuit related to spark timing)

The starting points in the left mag fire at TDC, Top dead center... which happens to be perfect for starting...

The other points are timed to be around 20 or 25° BTDC (before top dead center).

Since your mag was recently OH’d... it should be working properly...
 

But, with such difficulty... the left mag is suspect because it is the sole starting mag...
 

Check the mag’s part number to verify that it is the proper mag to do the left mag’s job...

 

You can read up on the electronic mags around here... search the word SureFly...

They go into the L mag’s spot to enhance the starting...

They provide a stronger spark which helps starting as well...

They are very new and don’t have much history to go on... but all looks good so far...

There have been a couple of minor install challenges typical of new products in the field... but nothing long lasting...

It would be wise to check your log books to identify what spark plugs are in there...

  • if they say champion...
  • if they are years old...
  • inspect, clean, and measure their resistance...

It is quite possible you have a common problem of old spark plugs... And, it would be too soon to replace a good mag, and leave crummy spark plugs in place...
 

Find the entry in the log where it mentions what plugs are in there...

PP thoughts only, stuff I read around here...

Was that helpful?

Best regards,

-a-

  • Thanks 1
Link to comment
Share on other sites

I spent some time with Matt this evening, a few comments:

Starter is turning the prop at a perfectly reasonable speed for engine start, that's not the root issue.

We practiced multiple cold and hot starts.  Nothing wrong with Matt's starting technique in either case.  All his practices and procedures are normal, and he's well-versed on how fuel/air/spark come together via priming, ignition switch, and mags.  I think it's very likely the reluctant starts are an issue with a marginally-functional component, just need to figure out which one.

In the fuel/air/spark trio, it seems unlikely air is the issue.  Air filter was recently replaced, and engine runs completely normally once started.

Turning to spark, it's a fine idea to clean, inspect, and test the plugs, as well as checking mag wiring and timing.  But this has been done recently by a well-regarded A&P at Matt's home airport.  Doesn't mean something might not have been missed, or that he shouldn't check these components again, but that's not where I'd start.

The idea of replacing the SoS system with electronic ignition to address a starting issue is not reasonable.  The SoS box is easy to remove and inspect, inexpensive to repair if worn, and perfectly capable of providing reliable starts for years on end.  I know this from 16 years' experience with the same engine and starting system here in the Denver area.  Electronic ignition is comparatively expensive, requires disconnecting and reconnecting ignition wiring (at the very least to remove the SoS) which can have its own issues, and we don't actually have enough information to know the current magnetos or SoS are actually the problem.  There can be principled debate on the value of electronic ignition for other reasons, but difficult starting is not one of them.

On that last note, it's important to understand the SoS system can make the desired buzzing noise, while generate a weak spark that is barely sufficient for starting.  Because the SoS system is straightforward to remove and bench-test, Matt and I think that's a good next step in debugging.

On the fuel side, we discussed the possibility the operation of the fuel servo is somehow marginal when the engine is not running, such that it feeds substantially more or less fuel to the flow divider during priming than desired, resulting in an overly rich or lean starting mixture.  But that seems like a stretch.  For now, my bet is on weak spark from the SoS.

  • Like 3
  • Thanks 1
Link to comment
Share on other sites

Great review Vance!

Lots of votes pointing towards the SOS box...

 

If checking everything possible...

The fuel system can be tested by doing the baby food jar test... a test for good fuel distribution amongst all four fuel injectors...

This is a great baseline test if your fuel system has seen lots of years of activity without much OH activity...

Or while the engine is running, test the GAMI spread... to get a good idea of the distribution...

PP extra thoughts...

Best regards,

-a-

Link to comment
Share on other sites

7 hours ago, Vance Harral said:

I spent some time with Matt this evening, a few comments:

Starter is turning the prop at a perfectly reasonable speed for engine start, that's not the root issue.

We practiced multiple cold and hot starts.  Nothing wrong with Matt's starting technique in either case.  All his practices and procedures are normal, and he's well-versed on how fuel/air/spark come together via priming, ignition switch, and mags.  I think it's very likely the reluctant starts are an issue with a marginally-functional component, just need to figure out which one.

In the fuel/air/spark trio, it seems unlikely air is the issue.  Air filter was recently replaced, and engine runs completely normally once started.

Turning to spark, it's a fine idea to clean, inspect, and test the plugs, as well as checking mag wiring and timing.  But this has been done recently by a well-regarded A&P at Matt's home airport.  Doesn't mean something might not have been missed, or that he shouldn't check these components again, but that's not where I'd start.

The idea of replacing the SoS system with electronic ignition to address a starting issue is not reasonable.  The SoS box is easy to remove and inspect, inexpensive to repair if worn, and perfectly capable of providing reliable starts for years on end.  I know this from 16 years' experience with the same engine and starting system here in the Denver area.  Electronic ignition is comparatively expensive, requires disconnecting and reconnecting ignition wiring (at the very least to remove the SoS) which can have its own issues, and we don't actually have enough information to know the current magnetos or SoS are actually the problem.  There can be principled debate on the value of electronic ignition for other reasons, but difficult starting is not one of them.

On that last note, it's important to understand the SoS system can make the desired buzzing noise, while generate a weak spark that is barely sufficient for starting.  Because the SoS system is straightforward to remove and bench-test, Matt and I think that's a good next step in debugging.

On the fuel side, we discussed the possibility the operation of the fuel servo is somehow marginal when the engine is not running, such that it feeds substantially more or less fuel to the flow divider during priming than desired, resulting in an overly rich or lean starting mixture.  But that seems like a stretch.  For now, my bet is on weak spark from the SoS.

Start with the simple things like making sure the switch it working properly and the p leads are not getting shorted out.   Last one around here was a shorted P lead.

Link to comment
Share on other sites

8 hours ago, carusoam said:

Great review Vance!

Lots of votes pointing towards the SOS box...

 

If checking everything possible...

The fuel system can be tested by doing the baby food jar test... a test for good fuel distribution amongst all four fuel injectors...

This is a great baseline test if your fuel system has seen lots of years of activity without much OH activity...

Or while the engine is running, test the GAMI spread... to get a good idea of the distribution...

PP extra thoughts...

Best regards,

-a-

So quick update:  Aircraft Accessories of OK sells overhauled starting vibrators for $380 and new ones for $450.  I bought a new one and it should arrive in a few days.

I haven't done the baby jar test yet.  I don't have much reason to suspect fuel distribution.  When doing my LOP setting via the JPI, the FF from lean to rich is usually within 0.3 GPH according to my ancient fuel flow monitor.  The engine runs great at about 8.3GPH and will run as low as mid 7s without too noticeable roughness.

My only slight concern with the FF is that sometimes when I try to really finesse the vernier to get from, say, 8.5 to 8.3 gph, leaning will sometime result in a fuel flow reading actually increasing. I chalk that up to my very old Hoskins but it is something I'm conscious of and do monitor.

cc @Vance Harral

  • Like 3
Link to comment
Share on other sites

13 hours ago, Matt Ward said:

So I know basically nothing about electronic mags.  Would I replace just one (the left?) and leave my existing right mag?  Then I'd remove the SOS entirely?

For the record, I agree that you’re not at a point to go to electronic mag.  Trying to solve a starting problem is not reason to switch - could still be a fuel issue or harness or plugs etc.

But to answer your question, you can just remove and replace the left mag.  You leave the right mag as is.  You unhook the SOS.  If you want to remove it you can.  You have to run one wire to the battery.  If the battery is in front, it’s easy.  If it’s in the tail, it’s more work.

Link to comment
Share on other sites

Quick update:  I ordered a new starting vibrator from Aircraft Accessories of OK ($450).  It arrived today.  I installed it in about 30 minutes.  There are two 3/8" bolts that can be accessed through the oil access door on the cowling.  The actual vibrator is on the co-pilot side of the instrument access panel.  There are two wires.  

After installing it, I fired up the engine a couple times and it seemed to start much quicker!  I'll need to have a few more starts before I can say for sure what the impact is, but so far so good.

Here are a couple side-by-side pics of the old and new.  If any aspiring electrical wiz wants my old one for research, it seems like there are a lot of SOS-type issues, let me know and I'm happy to donate it.

Edit: the sticker on the box suggests Bendix mags.  I actually have Slicks.  The model number of the vibrator (new vs old) is the same without the final letter.  My *guess* is my old SOS far pre-dates on my Slick mag conversion.  I called the shop and they didn't think it was any sort of issue but it was something I noticed.

 

IMG_4023.JPEG

IMG_4022.JPEG

  • Like 1
Link to comment
Share on other sites

I’m more and more confident this has solved my starting issues. @carusoam and @Vance Harral, I thought you guys were kidding when you asked me about getting it started in 2 or 3 blades, but that’s exactly what’s happening! Most starts have been cold and they are great. A few hot that have been excellent too. No occasion for flooded start yet. Thanks for all the help!

  • Like 3
Link to comment
Share on other sites

Matt,

One of these days... you will be giving similar advice to the next MSer...

Vance really knows his stuff...

I merely copy as much as I can remember...   :)

Or find the guy that knows his stuff... and invite them to the conversation...

MS has so many knowledgable people with all kinds of backgrounds...

Go MS..!

Best regards,

-a-

Link to comment
Share on other sites

On 8/27/2020 at 5:56 PM, Matt Ward said:

Quick update:  I ordered a new starting vibrator from Aircraft Accessories of OK ($450).  It arrived today.  I installed it in about 30 minutes.  There are two 3/8" bolts that can be accessed through the oil access door on the cowling.  The actual vibrator is on the co-pilot side of the instrument access panel.  There are two wires.  

After installing it, I fired up the engine a couple times and it seemed to start much quicker!  I'll need to have a few more starts before I can say for sure what the impact is, but so far so good.

Here are a couple side-by-side pics of the old and new.  If any aspiring electrical wiz wants my old one for research, it seems like there are a lot of SOS-type issues, let me know and I'm happy to donate it.

Edit: the sticker on the box suggests Bendix mags.  I actually have Slicks.  The model number of the vibrator (new vs old) is the same without the final letter.  My *guess* is my old SOS far pre-dates on my Slick mag conversion.  I called the shop and they didn't think it was any sort of issue but it was something I noticed.

 

IMG_4023.JPEG

IMG_4022.JPEG

I believe that Aircraft Magneto Service in Montana will test/ adjust your SoS box for next to nothing.  You’d have a spare when you need it in 30-40 years.

Clarence

Link to comment
Share on other sites

20 minutes ago, M20Doc said:

I believe that Aircraft Magneto Service in Montana will test/ adjust your SoS box for next to nothing.  You’d have a spare when you need it in 30-40 years.

Clarence

Sometimes fixing a weak SOS is as simple as filing/cleaning the points.

  • Like 2
Link to comment
Share on other sites

52 minutes ago, Mooneymite said:

Sometimes fixing a weak SOS is as simple as filing/cleaning the points.

That was the main issue with our SoS box when it got weak: the points were worn and mis-shapen.  They can be filed, or you can order replacement points.

The other usual culprit is the condenser (capacitor) that is part of the oscillatory circuit that causes the back-and-forth action of the vibrator.  The electrolyte in large capacitors ages, leaks through seals, etc.  The result is a capacitor whose actual capacitance is different than the design value, which affects the circuit.

Matt, I'm glad to hear a new SoS box seems to have resolved your issues!  Recommend that at your leisure, you procure a new condenser and new set of points, and install them in the old box.  This should not be expensive, and then you'll have a spare to keep on the shelf.

  • Like 2
Link to comment
Share on other sites

Hey Yves!

I went down Doc’s parts list...

Found Capacitor 10-164418...

Searched that number... said it was superseded by another one...

https://www.aircraftspruce.com/catalog/eppages/continentalnewcapacitors_07-05250.php

This could be dodgy coming from an ordinary PP... so confirm before going too far...
 

Missing KOSH still.... great memories from last year still.... :)

PP thoughts only, not a mechanic...

Best regards,

-a-

Link to comment
Share on other sites

6 hours ago, M20Doc said:

I believe that Aircraft Magneto Service in Montana will test/ adjust your SoS box for next to nothing.  You’d have a spare when you need it in 30-40 years.

Clarence

 

6 hours ago, Mooneymite said:

Sometimes fixing a weak SOS is as simple as filing/cleaning the points.

 

It's always amazed me that people don't understand the shower of sparks so they love to bad-mouth it, even though it's one of the simplest and most effective systems on our airplanes.  Plus you can replace the internal parts that wear out in about an hour for about $20.  Can't do that with a bad impulse coupler.

And it is also a significant safety enhancement:  the likelihood of a broken p-lead causing an accidental start is practically zero, unlike an impulse coupling.

 

  • Like 1
Link to comment
Share on other sites

17 hours ago, Mooneymite said:

Sometimes fixing a weak SOS is as simple as filing/cleaning the points.

I was gonna say, light filing of the points and replace the capacitor and it's probably essentially new again.   There's not much to those things.

10 hours ago, Andy95W said:

It's always amazed me that people don't understand the shower of sparks so they love to bad-mouth it, even though it's one of the simplest and most effective systems on our airplanes.  Plus you can replace the internal parts that wear out in about an hour for about $20.  Can't do that with a bad impulse coupler.

And it is also a significant safety enhancement:  the likelihood of a broken p-lead causing an accidental start is practically zero, unlike an impulse coupling.

I think the only significant downside to the SoS is the need for the battery (i.e., precludes the ability to hand prop with a dead batt), and that's probably not a practical issue for most people.

  • Like 1
Link to comment
Share on other sites

Matt, I'm certainly not taking anything away from what you've done.  I'm glad you're back up and running and happy for a reasonable price.

The price for the capacitor/condensor has gone up a bit- I'm now showing $42.95 for that part, but nothing else really wears out.  File the points, replace that capacitor, set the points per the manual, reassemble.

Actually very simple, but the catch is you have to find a mechanic willing to read the manual and give it a try.

TCMIgnitionVibratorManual.pdf

  • Like 1
Link to comment
Share on other sites

20 hours ago, Andy95W said:

Matt, I'm certainly not taking anything away from what you've done.  I'm glad you're back up and running and happy for a reasonable price.

The price for the capacitor/condensor has gone up a bit- I'm now showing $42.95 for that part, but nothing else really wears out.  File the points, replace that capacitor, set the points per the manual, reassemble.

Actually very simple, but the catch is you have to find a mechanic willing to read the manual and give it a try.

TCMIgnitionVibratorManual.pdf 2.5 MB · 3 downloads

Understood!  If I were more confident in my MX abilities I'd probably have tried that.  For me, the time-to-value just made sense to replace with new.  Either way, I'm super happy with the way the plane is starting now!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.