What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Do I have a bad mag? Could really use your help here.

jcarne

Well Known Member
Patron
I was hand propping (without plugs) to get oil pressure on my newly rebuilt engine. The impulse coupler on the left mag was doing it's clicking and felt normal. There was a definite click but didn't take a lot of resistance to overcome. After I got a slight oil pressure I went back and turned the prop some more. After quite a few blades the area where the click is got insanely tight! I could still get it to turn but it hit a hard stop at the normal impulse coupler snap spot. I stopped and came here in hopes that someone will hopefully give me some advice on what to do.

Should I pull the left mag and see if there is something wrong with the impulse coupler or is this normal? It sure didn't feel normal. There was also what sounded like a creaking sound coming from the left mag after it got tight. It only makes the sound when it is winding up the spring in the mag and ready to release. The engine also spins smoothly backwards.

The engine was ran for almost 2.5 hours at Aerosport but they used a slave left mag.

Could really use your guys' help on this one, I'm getting very frustrated with the project at this point...

Thanks in advance everyone
 
Last edited:
Jereme, Best you pull it off and have a look. It's pretty easy to do and for peace of mind... and dollars...
Russell
 
It should not do that and I would not run it. If the impulse fails, parts can fall into the engine. Remove the mag and see if the problem remains.
 
Pull it off. You won't like what happens if that drive end comes apart.

FYI- I've seen more than one mag eat itself right after overhaul or installation.
 
Correct Bob, you can only get it to about 30-40 PSI.

I will go ahead and pull the left mag. From videos I have seen I should be able to turn the mag and actuate the impulse coupler by hand correct?
 
If you can "feel" the resistance of the impulse coupler at the prop at all, and it is indeed the impulse coupler, then you have a big problem.

Also, spinning the engine with the starter is much more effective at "priming" the oil pump than swinging the prop by hand.
 
I was flying a few weeks ago and the tach signal from my magneto became erratic. The engine ran fine though and I didn't notice a thing. At that point it was probably running on my Electroair only because it wasn't just electrical noise. I flew a little further and landed at my destination.

I have no starter and always hand prop on the magneto only. The next day it wouldn't start. The impulse coupling didn't feel right and then it started binding, completely stopping engine rotation. So, I pulled the magneto. I could tell that the pawls on the impulse coupling were loose. I removed the gear and the impulse coupling shell and sure enough the rivets that both pawls rotate on had failed!

There is a service bulletin on those rivets for my magneto, which was brand new from Slick and only had 25 hours or so in service. Still waiting to hear on my warranty claim ...
 
Well this is the project that just keeps on giving... I'm starting to think I have some of the worst airplane luck in the world.

I pulled the mag, definitely a bad impulse coupler. The question now is what caused it? There was no lube at all on the impulse coupler assembly, specifically where the pawls and stop pin are. That seems like an area that would be lubed upon assembly due to the friction of metal on metal right there.
The pawls are definitely trashed. I found some metal on the mag spacer. Below is a pic of the two large fragments next to a 1/4" nut.

IMG_0121 by Jereme Carne, on Flickr

Next is a picture of one of the impulse pawls. Definitely damaged. Pretty sure this is where the large pieces came from. There are lots of tiny bits too magnetized to the end of the pawl as you can see.

IMG_0159 by Jereme Carne, on Flickr

Now the big question. The gear train.

I looked it over as best I could as there isn't that great of access behind the engine and found one tooth on the mag idler gear that has me wondering. It looks like the corner of the gear is slightly misshaped. It is hard to tell though. It feels perfectly smooth but doesn't look like it in the picture below. I am also really confused as to why it is just on the corner. It almost seems like it was dropped onto that corner.

It looks really bad in this picture. But can't tell if light is playing tricks as you will see in the following pics.

IMG_0152 by Jereme Carne, on Flickr

Hardly noticeable in this picture.

IMG_0151 by Jereme Carne, on Flickr

Less noticable in this pic but definitely looks different than the other gears.

IMG_0157 by Jereme Carne, on Flickr

Any idea here guys?

Before you jump the gun and say that hand propping didn't generate enough oil pressure to lube the pawls lets keep in mind that Lycoming 1241C lets you spin the engine for more than a minute with the starter (taking breaks of course) and not obtain oil pressure before taking a closer look at things. Even then they say minimum oil pressure during pre-oiling is 20 psi. I hand spun the prop for about 10 seconds on two occasions and got the oil pressure in the 30s.
 
Last edited:
My concern, after seeing your pictures, is the pieces of metal you found - and what about the ones that you didn’t? Where are they now? A brand new engine with pieces and slivers of metal running around inside is not a good thing.

Paul
 
My concern, after seeing your pictures, is the pieces of metal you found - and what about the ones that you didn’t? Where are they now? A brand new engine with pieces and slivers of metal running around inside is not a good thing.

Paul

True Paul. Although I think most if not all was captured in the mag spacer. The gears were covered with a thick assembly lube and when I was wiping that off to get a better look at the gears I never found another piece of metal. Not saying it couldn't of happened but it doesn't appear to have. If metal did enter the rear case it should of dropped down into the sump which I would find in the screen eventually?

Unless anyone else has any ideas on course of action I guess all I can do is call Aerosport on Monday and see what they say.

If anyone knows why this may have happened I'm all ears. I can't find a similar case anywhere else on the web.
 
I was hand propping (without plugs) to get oil pressure on my newly rebuilt engine....The impulse coupler on the left mag was doing it's clicking and felt normal. There was a definite click but didn't take a lot of resistance to overcome. After I got a slight oil pressure I went back and turned the prop some more. After quite a few blades the area where the click is got insanely tight! I could still get it to turn but it took a large amount of force on the prop to do so, much larger than before.

I think this is where you experienced some kind of debris dropping into the accessory gear assembly. That may have had nothing to do with oil pressure - just the rotation of the engine may have dropped something into the gears.

... I think most if not all was captured in the mag spacer....If metal did enter the rear case it should of dropped down into the sump which I would find in the screen eventually?

I think both are bad assumptions. You really don't know where the metal came from or how much. And whether there is still some there or some consequence of rotating the crankshaft when it seemed very tight. This might be just about the impulse coupling, maybe the gears as well. Maybe more.

There are a couple of possible failure modes here and I think the starting point is to discuss this with the engine builder before any further turning of the crankshaft. The photos are excellent, but they might want to see the actual metal debris you removed.
 
I think this is where you experienced some kind of debris dropping into the accessory gear assembly. That may have had nothing to do with oil pressure - just the rotation of the engine may have dropped something into the gears.



I think both are bad assumptions. You really don't know where the metal came from or how much. And whether there is still some there or some consequence of rotating the crankshaft when it seemed very tight. This might be just about the impulse coupling, maybe the gears as well. Maybe more.

There are a couple of possible failure modes here and I think the starting point is to discuss this with the engine builder before any further turning of the crankshaft. The photos are excellent, but they might want to see the actual metal debris you removed.

Thanks Dan. I think you're right. I will talk to the builder and see what they recommend. I just hope it doesn't need another tear down; that might just make me sell the project at a steep discount.

Just to clarify though. It did get tight somewhat progressively but rapidly. When I noticed this happening I stopped. I didn't blindly force the prop with all my might. When I took the mag off, the pawl that was on the stop pin had so much friction between the two that I couldn't actuate it by hand. I eventually freed up the mag and it spins fine now, but for some reason there was a lot of friction between the pawls and the stop pin. So much so that is sheared some of the metal off of the pawls. In others words, the mag impulse assembly wasn't kicking the pawls off of the stop pin for some reason.
 
Last edited:
Most likely you have the wrong impulse coupler or the wrong magneto installed. Verify the dataplate first for correct direction of rotation.
 
Thanks Dan. I think you're right. I will talk to the builder and see what they recommend. I just hope it doesn't need another tear down; that might just make me sell the project at a steep discount.

Hang in there and maybe take a break for some fresh air! I am sure that every project has its ups, and downs that always seem worse at the time. ;)
 
Unless anyone else has any ideas on course of action I guess all I can do is call Aerosport on Monday and see what they say.

Good Find!! It takes a careful observation to find these things, you did well!!!

Regardless of what happened, calling Aerosport is the first action, That tooth is definitely deformed. Not acceptable.

I will tear into anything, but IMO, they own this engine at this point.
 
Most likely you have the wrong impulse coupler or the wrong magneto installed. Verify the dataplate first for correct direction of rotation.

It is the correct mag and impulse coupler. Just verified it. Is the mag gear supposed to have a little bit of play in it though? I can definitely rattle the gear slightly a bit on the mag.

Hang in there and maybe take a break for some fresh air! I am sure that every project has its ups, and downs that always seem worse at the time. ;)

Thanks Paul. I'll get over it eventually. It's just super demoralizing to potentially have to send this engine in again for another tear down. It's an emotional roller coaster of looking forward to first flight and being only days away from it to having to take an engine off for a 3 month delay. Life goes on...

Good Find!! It takes a careful observation to find these things, you did well!!!

Regardless of what happened, calling Aerosport is the first action, That tooth is definitely deformed. Not acceptable.

I will tear into anything, but IMO, they own this engine at this point.

Thanks for the kind words Bill. I'll definitely contact them. I just hope they make it right.
 
As Paul said, hang in there. I would venture to say not too many get through an entire build without some trying issues.

I had 34hrs on my "rebuilt" engine when it started making metal. Turns out the reground tappets were not done correctly and took out the cam. New cam/lifter kit, pistons, bearings, oil pump, cylinder hone etc etc and away we go again. Very discouraging but it could have been worse.

As my AME friend says, better to find it on the ground than in the air!

Keep the faith!
 
Metal

Those small pieces look like they could possibly be pieces of cotter pin. Can you confirm that there is a cotter pin installed on the mag gear. For a Bendix mag that cotter pin is a Bendix part number and is not a standard fractional size pin. Also the mag cotter pins require trimming the ends after installation.
 
As Paul said, hang in there. I would venture to say not too many get through an entire build without some trying issues.

I had 34hrs on my "rebuilt" engine when it started making metal. Turns out the reground tappets were not done correctly and took out the cam. New cam/lifter kit, pistons, bearings, oil pump, cylinder hone etc etc and away we go again. Very discouraging but it could have been worse.

As my AME friend says, better to find it on the ground than in the air!

Keep the faith!

Ouch, sorry to hear about your troubles at only 34 hours. Thanks for posting.

Those small pieces look like they could possibly be pieces of cotter pin. Can you confirm that there is a cotter pin installed on the mag gear. For a Bendix mag that cotter pin is a Bendix part number and is not a standard fractional size pin. Also the mag cotter pins require trimming the ends after installation.

Here is a pic of the cotter pin. Looks normal to me but then again I have never installed one on a mag.

IMG_0162 by Jereme Carne, on Flickr
 
Last edited:
Since you verified the correct part #'s and rotation the only other thing I'm guessing it could be is improper heat treatment of the pawls. No it is not normal for the gear to rock like that. The rotor shaft end is a tapered shaft with a woodruff key. The gear should be tapped onto the shaft where it will lock onto the taper. The key is just a backup.
 
After the last Slick SB on the Impulse mags and the warnings, I bit the bullet and installed a SureFly on the left (impulse) side. Very simple installation and peace of mind.. starts better, too. Maybe the shop would give you some credit for the bad mag?
 
Something is wrong with that magneto to make the drive gear loose on the shaft like that.

My unofficial opinion is that it' likely that wiggle is what caused a misalignment, causing it to bind up and resulting in the rest of your problems.

Who put that magneto together and installed it on the engine?
 
Though the impulse coupler is an old school solution to a problem that was solved with electronics more than 50 years ago and remains a mechanical nightmare, I thought that this self disassembling hand grenade was "fixed" by the AD years ago. This thread illustrates that the threat remains. It's also important to consider this issue if you are thinking of adding an EI and wondering which mag to replace. When I went to my first Pmag years ago, it replaced the impulse mag just for this reason. And this also adds some data for the debate concerning the relative reliability of the SDS crank trigger.

Sorry about the bad luck here, but thanks for posting.
 
Something is wrong with that magneto to make the drive gear loose on the shaft like that.

My unofficial opinion is that it' likely that wiggle is what caused a misalignment, causing it to bind up and resulting in the rest of your problems.

Who put that magneto together and installed it on the engine?

I think you may be right about the misalignment. The magneto was put together and installed by the engine builder. I received the engine with it already installed. The engine was test run but the report says that it was done with a slave left mag.

Though the impulse coupler is an old school solution to a problem that was solved with electronics more than 50 years ago and remains a mechanical nightmare, I thought that this self disassembling hand grenade was "fixed" by the AD years ago. This thread illustrates that the threat remains. It's also important to consider this issue if you are thinking of adding an EI and wondering which mag to replace. When I went to my first Pmag years ago, it replaced the impulse mag just for this reason. And this also adds some data for the debate concerning the relative reliability of the SDS crank trigger.

Sorry about the bad luck here, but thanks for posting.

Ya something tells me I'm going to just replace it with a Pmag. First I am waiting to see if the engine shop will make this right; they have been great to deal with so far. It sounds like from a few people that the mag gear wasn't installed properly.
 
mags

I'm now thinking that a stray piece of metal got between the mag gear and the idler gear and damaged both the mag and the idler gear and perhaps more. There are very likely some more small pieces of metal in the sump.
 
Mag

One more thought-the mag gear nut is a special nut. It is a matter of luck if the cotter pin lines up within the torque specs for the nut. It is possible that the nut was loosened to line up the cotter pin.
I think the small pieces of steel inside the engine are likely from something dropped there during assembly. This could be another possibility that a stray piece between the mag gear and idler gear bent the mag shaft or caused other damage to the mag.
 
One more thought-the mag gear nut is a special nut. It is a matter of luck if the cotter pin lines up within the torque specs for the nut. It is possible that the nut was loosened to line up the cotter pin.
I think the small pieces of steel inside the engine are likely from something dropped there during assembly. This could be another possibility that a stray piece between the mag gear and idler gear bent the mag shaft or caused other damage to the mag.

After thinking about it some more I'm almost positive that all of the metal likely came from the mag impulse pawls. The forces built very rapidly as I was spinning the prop quite fast and the last "click" I heard was very loud indeed. The corner of the pawl just sheared off it would appear. You can without question see where metal is missing from them.

I'm in contact with the engine builder and he is in contact with Champion to see what needs to be done. He said in his 30 years of experience he has never seen these pawls just self destruct like this on a new mag. Worn down ones yes but never destruction.
 
Here is a video of of the gear movement I mentioned in an earlier post. I don't know if it's normal or not. It seems pretty sloppy to me.

That looks normal for an impulse mag. The gear is not locked onto a tapered shaft for an impulse mag. That is only true for a non-impulse mag.
 
That looks normal for an impulse mag. The gear is not locked onto a tapered shaft for an impulse mag. That is only true for a non-impulse mag.

Ya that is what the engine shop indicated too. May be a moot point now though as I don't think there is a chance in heck I'm putting another impulse coupler in this engine.
 
Damaged Gear

The pictures you show of the accessory case gear in post 11 clearly show a damaged gear tooth. In my opinion, the accessory case needs to come apart at a minimum to replace that gear and search for remaining debris. I suspect the binding you felt when hand turning the engine was a piece of the debris wedging itself between the mag gear and the accessory case gear teeth which is what left the visible witness mark. If that’s the case it also may have excessively side-loaded the mag rotor shaft because the the debris would have been trying to force the gears out of mesh. The mag should also be disassembled so the rotor shaft can be checked for straightness.

Skylor
 
Last edited:
The pictures you show of the accessory case gear in post 11 clearly show a damaged gear tooth. In my opinion, the accessory case needs to come apart at a minimum to replace that gear and search for remaining debris. I suspect the binding you felt when hand turning the engine was a piece of the debris wedging itself between the mag gear and the accessory case gear teeth which is what left the visible whiteness mark. If that’s the case it also may have excessively side-loaded the mag rotor shaft because the the debris would have been trying to force the gears out of mesh. The mag should also be disassembled so the rotor shaft can be checked for straightness.

Skylor

I'm still waiting to hear back from the shop on contacting Champion but I won't feel comfortable flying this engine until the idler gear is replaced, sump/gears scavanged for more metal, and I want to see NDT done on the crankshaft gear as well as see if the pin was damaged. It had to have taken a fair amount of force to do that to a gear.
 
Good Call.

I'm still waiting to hear back from the shop on contacting Champion but I won't feel comfortable flying this engine until the idler gear is replaced, sump/gears scavanged for more metal, and I want to see NDT done on the crankshaft gear as well as see if the pin was damaged. It had to have taken a fair amount of force to do that to a gear.

That's the right approach! This may seem like a pain right now but in the long run this is the safest path forward and will give you peace of mind down the road!

Skylor
 
Alright, let's give this thread some closure. After one of the longest shipping delays I have ever experienced the mag made it back to Aerosport in early January. They noted that the flyweights on the impulse coupler appeared to be made of a softer and darker metal than an older mag they compared it to. It would certainly explain why this impulse coupler decided to fail.

Taking it a bit further I saw my friend Wirejock was selling his two mags so I had him take a picture so I could visually compare. Here is the side by side with his mag on the left and mine on the right. The metal certainly looks different! Larry's is consistent with other mags I have seen on the internet as well.

mags by Jereme Carne, on Flickr

I'm not sure what caused this manufacturing defect (wrong metal used or missed heat treat?) but the engine is now repaired and was started again two days ago. See post 614 in my build thread on how the repair went. (good pictures in that one)

Thanks again to everyone that helped me out on this!
 
Back
Top