Slick Magneto 6314 failure at 700hrs

Sorry, I don’t know how to start an entirely new thread on here so I tapped into this one about slick mags.

Yes…the crank is exactly 25 BTDC and I use a digital inclinometer on the prop to find that. Additionally, last year I discovered the drive gears look identical for both mags but are 2 P/Ns and they were swapped so I installed them correctly on these new mags. Previously, the mags were clocked all the way out in the opposite direction. The mags are new, the internal mag timing is correct and they are stabbed to the engine properly.
I am wondering if it is possible that the cam is clocked one tooth off when the engine was rebuilt?
 
I wouldn’t think that would be possible because the starter ring gear marks also line up and indicate 25 BTDC also when I use the inclinometer. If the cam was clocked wrong there would be no way both indicators would be telling me the same thing. The valve lap would be off if that was the case.
 
Which drive does yours have? A tanged drive like this one,

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Or a gear like these one?

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If it's the tang drive, then perhaps something's wrong in the mag. Was it just overhauled? The tech might have got the points cam in the wrong position, for a mag that rotates the other way, for example. Or the distributor gears aren't timed right.

Or maybe you're just turning the mag the wrong way. See next paragraph.

If it has a gear, I'd recheck the mag and make sure the red tooth is in the window properly. If it is, and if you have the turn the mag far over to get the points to open, you might be rotating the mag the wrong way and the points are riding up the backside of the cam for the cylinder in the previous firing order. Look at the mag's tag. It will have the rotation in the mag model number. S6LN, for example, is a left-hand rotation mag, as viewed looking at the mag's drive end. Counterclockwise. If it's a LH mag, you need to rotate the mag the opposite to that to get the points open. S6RN is a RH mag. It rotates clockwise as seen looking at the drive end.
 
Some Bendix magnetos will end up close to one end or the other of travel on the magneto slots even when everything is perfect. I’ve only seen this happen on magnetos with a drive gear installed on them. This can usually be corrected by installing the magneto one tooth forward or back from the original attempt.

If you have the tang drives and rubber cushions in the engine then there is a chance the gear in the engine is indexed wrong. It would have always been indexed wrong however, unless the gear was pulled out at some point after the engine was assembled. Either way, the problem likely would have shown up before now if that was the case.

This is easy enough to overcome with a little trial and error. Don’t overthink it.
 
Clocking of the Drive Gears is not identical.

If you reverse the gear on the Impulse Mag it may help.

Can’t do on the non- impulse mag .

Some newer gears have 2 key ways to facilitate the timing process .

If engine/cam were off a tooth rpm would be low.

You can verify by bringing a cylinder to TDC and noting Rocker Arms on opposing

cylinder.

Lycoming has a SI on this.
 
WannFly said:
You can be on top of mx game, do everything by the book, things will still happen.

Preventative mx doesn’t always prevent jack
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That’s right. We also recently had one go bad about 150 hours out of the 500hr inspection from AMS. They took care of it at no charge.

You can have failures at anytime, but if someone’s neglecting important maintenance it’s much more likely to bite them.
 
WannFly said:
Once I get the mag back I am going to start chasing the P Lead / harness/switch rabbit hole
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When testing the leads make sure (while you’re testing) that you wiggle the lead along it’s entire routing. I saw one recently that would only fail when the lead was moved about while testing. It was causing an intermittent problem. Unfortunately a maintenance facility had recently checked them and signed the lead check off as good when they were not.
 
It is possible that the valve timing is messed up on your engine depending on the original assembler's attention to detail.

I diagnosed one on the AOPA forum many years ago. And I had a Pinto (a new car then) that was factory assembled off by one timing belt tooth.

Just don't ask me what the valve overlap timing to TDC should be. Best to compare to another engine.
 
Here's more background. I have Bendix mags with the single slot drive gear. They are both installed correctly. When I bought this plane 5 years ago the engine was just overhauled...and both mags were clocked to one side (The opposite direction) of where they are clocked now. The previous mags were all the way at one end of the range (Left mag had no more advance & right mag had no more retard left). I discovered the drive gears were swapped on the mags (Probably when installing on the new engine) and I was told by Kelly Aero and Aircraft Magneto service they see this all the time. NOW, I installed new mags from Aircraft MS and they are clocked maxed out but in the opposite direction (no more advance on the right & no more retard on the left)...after I swapped the gears to the correct mag.

SO...by swapping the drive gears the problem shifted to the other end of the spectrum...and this is on both mags!
Prior to installing the new mags I verified the points opened approx 10 degrees past the E-gap position...just as they should (On both mags). Now, I don't have the $250 degree plate that you install on the mag to set E-gap...but it was close enough to 10 degrees that it wouldn't have maxed out the mag positions all the way to one side...and I doubt AMS set the points wrong on both mags. If that were true then the previous mags from California would have had the same issue. Not much odds on that.

Additionally, I experimented with the RH mag and stabbed it one tooth to the right and then one tooth to the left. When I did this the mag would NOT time at all. The points wouldn't open during the entire range of rotation. I am now wondering if the cam is off a tooth? Is this possible and has anybody ever seen this?

If the cam is off by one gear it would make sense because it drives both mags. However, the engine runs perfectly at all ranges of flight and ground. Here's the weird thing! The starter ring gear lines up with the 25 degrees BTDC marks when I set the #1 to 25 BTDC. I use a digital inclinometer on the prop to remove all backlash and I am dead center at 25 BTDC when I stab the mags...unless there are too many gnats flying around the hangar that morning...LOL. AND...both valves are closed at TDC and 25 BTDC so they valves are lapping as they should.

With 12 bolts on the starter ring gear that might logically allow it to be aligned incorrectly by following the initial installation of the cam incorrectly? Has anybody ever heard of a cam being installed one tooth off and the engine working normally?
This is driving me bat SH!@$%
 
BTW...I'm and A & P...just not a very experienced one on GA aircraft. All my previous experience is on heavy turbine jets.
 
You should grab a light-aircraft A&P to have a look at it. There is a simple reason somewhere. Your engine is OK. It's a mag or poitioning problem.
 
Cherokee Lover said:
If the cam is off by one gear it would make sense because it drives both mags. However, the engine runs perfectly at all ranges of flight and ground. Here's the weird thing! The starter ring gear lines up with the 25 degrees BTDC marks when I set the #1 to 25 BTDC. I use a digital inclinometer on the prop to remove all backlash and I am dead center at 25 BTDC when I stab the mags...unless there are too many gnats flying around the hangar that morning...LOL. AND...both valves are closed at TDC and 25 BTDC so they valves are lapping as they should.

With 12 bolts on the starter ring gear that might logically allow it to be aligned incorrectly by following the initial installation of the cam incorrectly? Has anybody ever heard of a cam being installed one tooth off and the engine working normally?
This is driving me bat SH!@$%
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It's driving you crazy because there is a misunderstanding. A lack of experience with piston engines in general seems to be hurting you, and you're overthinking things.

The cam being off a tooth will not affect the magnetos in any way. Further, neither magneto is driven directly off the cam. The 12 bolts on the starter ring gear that you're referring to likely hold on part of the spinner and have zero relevance in the timing marks being lined up correctly. The starter ring gear is indexed to the crankshaft and has nothing to do with the camshaft being timed properly or not.

An engine will not run "normally" with the cam timing being off. As long as the cam timing is close it would likely run but be down on power.

So, back to the question at hand. As I mentioned in my previous post, sometimes the magnetos end up close to the end of their travel when everything is perfect. I believe this is because some of the machine work performed on the magneto gears is random. A different gear may get it closer to center if it is really bothersome, or you may be able to move the magneto over a tooth and straighten it out. Or if the timing you need can be achieved it could just be left alone.

These are simple engines, I have yet to find one I can't make right without going to extraordinary lengths.
 
Thanks for the feedback. Per the overhaul manual it states that the left crank idler gear needs the timing marks aligned with the cam and crank with #1 piston at TDC for indexing. I am assuming that if that gear is off it would cause the issue with the left mag…and I will verify if I can see it with the mag off during annual. As far as the right hand idler gear…the manual says their is no specific marks or orientation and that how it is installed is irrelevant. I am assuming that gear needs re-positioned. My research and troubleshooting has determined these are the only remaining things that could cause this.

The manual doesn’t state this…but I would assume it’s a good learning point for overhaul assembly. The accessory cover should be tacked in place and the Mags should be dry fitting and timing position verified before final installation of the accessory case cover.

Only option I have now (Until next overhaul) which BTW I will be VERY involved in next time…is to replace the right mag drive gear (On the mag) with the double slot and install it 180 out. That should place the mag to the high side of retard…giving me plenty of advance to play with.

jim
 
Are you sure you're using the mag timer properly? The correct mag timing is when the points OPEN. The old neon-light timers light up when the points open; many of the newer LED timers have the light go OUT when the points open. The face of the tester will tell you what to look for. I've seen a real big mistiming problem when the mags were set with points closing at the timing mark. It doesn't run well at all. The exhaust got real hot with the timing so badly retarded.
 
Yes…my lights go out when the points open on my synchrophaser
 
I also verified my E-gap was approx 10 degrees. Both mags are brand new and I had the same problem with the previous mags.
 
Whether you're using the Eastern Tech "Buzz-Box" or the LED Magneto Synchronizer you get an audio signal when the points OPEN
 
Cherokee Lover said:
Thanks for the feedback. Per the overhaul manual it states that the left crank idler gear needs the timing marks aligned with the cam and crank with #1 piston at TDC for indexing. I am assuming that if that gear is off it would cause the issue with the left mag…
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The left gear is an idler gear that drives the cam. The marks are to make sure the cam timing is correct. There is nothing of significance with the gear placement when it comes to the magneto, unless you have a 540 with the rubber drive cushions.
 
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