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Sticky valve?

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Brantel

Well Known Member
Sticky valve or maybe not?

For the engine experts out there....

Preamble:

Leaving Osh just about passing the edge of the D, bam! Sounded like something smacked the bottom of the plane with a dead blow hammer! Scared the pooooo out of my wife! I felt nothing in the controls, no shudders, nobody around me visually, nobody around me on the ads-b, quick glance at the tail and it is all there, quick shake of the stick and it all still works, quick look at the wings for dents or blood and nothing. I thought we must have hit a bird with the gear or something. Nerves calmed down and we keep going. Due to weather had to spend the night in Danville Il. Checked the plane out real good. No bird strikes. I removed the cowl and checked everything firewall forward and found nothing. Fast forward to departure morning and we blasted off in severe clear with 1:49 to go. On the climb up to 9500 and I got another bang! Just like the one coming out of Osh. Then a few more bumps from the engine a few minutes apart but then they went away. I realized that these might be after-fire bangs from a sticky valve. Normally my engine runs like a sewing machine. Never has had morning sickness. Stayed high till we had our home field made, in the rapid decent from 9500ft, got a couple more bumps from the engine. These were more than the normal downwind pop you sometimes get from closing the throttle too fast. Nothing will prepare you for how a sticky valve will scare you when it sticks while in cruise! I am certain that my wife will need new underwear!

So now I am ready to wobble test/ream the guides on all 4 before any additional flights! I am not fooling around with this kind of stuff. A miss or after-fire bang every now and then seems like a warning sign of an imminent bent pushrod or worse!

To clarify, the after-fire events I have seen have been one cycle events. Bang and then smooth again. No rough running for consecutive cycles. When it is running smooth, it is really smooth. No time to see any changes in EGT's.

Questions:

Can a sticky exhaust (open) valve cause an after-fire thru the exhaust for one cycle? If so, how does this happen if the valve is stuck open? One would think that if it is stuck open, it would not draw in any fuel on the intake stroke or be able to make any compression on the compression stroke?

What else could cause such a thing? I am already committed to the wobble test/reaming procedure but want to ensure I am on the right track. Since I have one Pmag and one Mag, I would thing the chances of late ignition timing to be slim to none?? I checked the intake and exhaust for leaks, blown out gaskets, cracks etc. None found. I still got an RPM rise at shutdown when I pulled the mixture.

Thanks for any comments or advice. I am rounding up the stuff I need to do the wobble test/reaming. The price Lycoming wants for the official tools is ridiculous so I will be making my own. Already have the reamer required. I will be using my friend Mike Bullock's awesome thread as guidance on how to perform the reaming operation as needed.
 
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Brian,

Just one thing to check - I was getting some "backfire bangs" on Tsam a few months back when I leaned. This is on an engine that has always been smooth as glass, so I was concerned. It was attributable to a bit rougher running on one P-Mag, and since I had about 600 hours on the engine and P-Mags, I decided to pull them and send them to Brad for a checkup and software verification. WHen I took them off, I did a resistance check on the ignition leads, and sure enough, two were way out of the spec - the same two that, it turned out, had significant corrosion on the end that plugged in to the P-Mag. I got some new leads from Brad, and once again, the engine is smooth.

So lesson - high resistance on the P-Mag plug wires can lead to an after-fire. They should be checked every year at annual - the spec is given as Ohms per inch, so you have to measure the length of each lead and do the math, but it doesn't take long.

Much less invasive than taking the engine apart!

Paul
 
I attended the lycoming class at osh on smooth valve operations and what you described is exactly what they said the symptoms of a sticky valve are. They said if it happens make sure your push rods are straight, if the valve sticks bad enough it can bend the rods/tubes.
 
So I have started the troubleshooting session. At this point I have the cylinder exhaust valves stripped down to just the valve in the guide.

I can feel no evidence of stickiness. Slick as hot butter. I am still going run the reamer thru all 4 next trip to the hanger just to ensure a nice baseline.

Paul, I am going to check the wires per your post above for both cross talk and high resistance.

Other than ignition, what the heck else could it be if there are no exhaust gasket leaks or cracks and no intake leaks that I can find? (I have one impulse coupler mag regular aircraft plugs and wires and one Pmag with car plugs and wires)

Is it possible for the stickiness to be on the cam side of things with the lifter/tappet?
 
Brian,

Have you checked the intake valves? While the exhaust valves are typically the culprit, I wouldn't leave it out of the realm of possibility for the intakes to be sticking.

When I had a sticky valve issue, it was much more pronounced than just a blip here and there....it was a major event where I lost EGT in #2 and CHT was rapidly decreasing over the time of the occurrence. Did your engine monitor report anything abnormally other than Shantel squeezing on to your hand for dear life?

Strange enough, on taxi out of SnF and Osh this year, my #1 cylinder exhibited morning sickness right after startup during taxi. EGT's drop off and the engine runs rough as heck. After cycling the throttle, everything smooths out and continues to run smooth for the remainder of my journeys. Something to do with recent storms me thinks? These engines are more complicated than the little man in the canoe!
 
how many hours on the engine? what was the wobble measurement value?
a new engine is set up with about .010 play. a worn out guide measures about .035. a mid time engine should be about .022.
 
I can feel no evidence of stickiness. Slick as hot butter. I am still going run the reamer thru all 4 next trip to the hanger just to ensure a nice baseline.

Forget feel. Measure. And don't ream unless you need it.

...what the heck else could it be....?

A little water.

Is it possible for the stickiness to be on the cam side of things with the lifter/tappet?

No.
 
how many hours on the engine? what was the wobble measurement value?
a new engine is set up with about .010 play. a worn out guide measures about .035. a mid time engine should be about .022.

~400, still waiting on the fixture to do the proper wobble test. Even though the valves feel great, I want to get a baseline reading on them for future reference.

Eyeball and finger engineering looks and feels like they are OK but I want to test them properly. I already have the dial indicator, just waiting on the fixture and extension.
 
Forget feel. Measure. And don't ream unless you need it.



A little water.



No.

Thanks Dan, plan to follow your advice. Waiting on the fixture to do the proper test. Already have the dial indicator.

As for water, will it cause an after fire pop?

Good to know to forget worrying about the cam side of things!
 
Brian,

Have you checked the intake valves? While the exhaust valves are typically the culprit, I wouldn't leave it out of the realm of possibility for the intakes to be sticking.

When I had a sticky valve issue, it was much more pronounced than just a blip here and there....it was a major event where I lost EGT in #2 and CHT was rapidly decreasing over the time of the occurrence. Did your engine monitor report anything abnormally other than Shantel squeezing on to your hand for dear life?

Mike, will check intake as well.

No indications from the EMS. I have looked at the trends and nothing to report. It was too fast for anything to respond. Like 1 cycle fast each time it happened.
 
Are you sure that is was an explosion in the exhaust? While I have never had a sticking valve, your symptoms don't match my expectations. I would expect the affected cylinder to go cold for a period until the valve free'ed up. I would not expect the valve to stick for just one cycle.

In my opinion, the most likely cause of a single cycle explosion in the exhaust manifold is ignition. If a plug doesn't fire, the raw gas goes into the manifold and if it fires the next cycle. The following hot gas ignites the raw fuel from the previous cycle. It's been a while, but I recall learning that the exhaust from the previous cycle is no longer hot enough to ignite raw fuel. You only get ignition when raw fuel is dumped and the following cycle, which is hot enough, will ignite it. Or the exhaust valve remains open a bit and the flame exits the valve, igniting the charge.

While unlikely in your case, overly lean mixtures can also cause ignition in the exhaust (mixture is too lean to burn) I had this on a motorcycle years ago. However, in those cases it was more unpleasant noise and far from a "bang" that I would expect to hear scare my wife wearing ANR headsets.

A leak in an exhaust gasket can also cause ignition in the exhaust, but It would not be limited to highly isolated events like you are experiencing

Larry
 
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Are you sure that is was an explosion in the exhaust? While I have never had a sticking valve, your symptoms don't match my expectations. I would expect the affected cylinder to go cold for a period until the valve free'ed up. I would not expect the valve to stick for just one cycle.

In my opinion, the most likely cause of a single cycle explosion in the exhaust manifold is ignition. If a plug doesn't fire, the raw gas goes into the manifold and if it fires the next cycle. The following hot gas ignites the raw fuel from the previous cycle. It's been a while, but I recall learning that the exhaust from the previous cycle is no longer hot enough to ignite raw fuel. You only get ignition when raw fuel is dumped and the following cycle, which is hot enough, will ignite it. Or the exhaust valve remains open a bit and the flame exits the valve, igniting the charge.

While unlikely in your case, overly lean mixtures can also cause ignition in the exhaust (mixture is too lean to burn) I had this on a motorcycle years ago. However, in those cases it was more unpleasant noise and far from a "bang" that I would expect to hear scare my wife wearing ANR headsets.

A leak in an exhaust gasket can also cause ignition in the exhaust, but It would not be limited to highly isolated events like you are experiencing

Larry

Larry,

I agree, it is a puzzle.

Fairly certain that it is an after fire bang. It is loud, you can feel it in the floorboard and at this point has only been one cycle at a time when it happens.

I am also leaning toward ignition. Going to ohm out the Pmag wires per Paul's suggestion above and I am also going to send the PMag in for a checkup. Will perform a good inspection of the regular mag as well. The only problem I have with thinking ignition is the fact that I have 2 of them of different types. One would think that at least one of them would fire. The ground mag checks are fine. I forgot to do a full power check in the air.


I don't think it is a lean mixture issue. The engine has been responding normally to mixture knob adjustments. The issue I am experiencing does not feel like the normal roughness that one gets when leaning too much.

I have looked for blown gaskets and have not found any signs. I use the blow proof ones on the exhaust that can leak but typically don't blow out.
 
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As for water, will it cause an after fire pop?

It can be real hard to judge exactly what you felt and heard. For example, a momentary power interruption of more than one cylinder can bang the pipes against an A-model's mount tubing, or the bottom of the firewall.

Always start with the simple stuff. Checked the gascolator lately? If good, it's one simple thing eliminated.
 
It can be real hard to judge exactly what you felt and heard. For example, a momentary power interruption of more than one cylinder can bang the pipes against an A-model's mount tubing, or the bottom of the firewall.

Always start with the simple stuff. Checked the gascolator lately? If good, it's one simple thing eliminated.

Will do! Thanks for the help!
 
I have looked for blown gaskets and have not found any signs. I use the blow proof ones that can leak but typically don't blow out.

You're not looking for a blown gasket, just a leak. A loose flange or missing chunk of gasket. During the exhaust stroke you get a strong volume of gas moving and it creates a negative pressure. A leaking gasket will allow air in which will cause any unburnt fuel to ignite (They started adding air into the exhaust in the 70's to combust remaining fuel in the exhaust to reduce the carbon emssions before they had FI to better manage AFR). Again, this shouldn't create enough energy to feel anything in your floorboards, just noise.

I still struggle to see how any combustion in the exhaust pipe could cause something you feel in the floorboards or creating something referred to as a "bang." Maybe Paul can describe what he heard / felt when he had this issue. This has never happened in my plane, only cars and bikes. I can't help but wonder if it is something else.

Larry
 
You're not looking for a blown gasket, just a leak. A loose flange or missing chunk of gasket. During the exhaust stroke you get a strong volume of gas moving and it creates a negative pressure. A leaking gasket will allow air in which will cause any unburnt fuel to ignite (They started adding air into the exhaust in the 70's to combust remaining fuel in the exhaust to reduce the carbon emssions before they had FI to better manage AFR). Again, this shouldn't create enough energy to feel anything in your floorboards, just noise.

I still struggle to see how any combustion in the exhaust pipe could cause something you feel in the floorboards or creating something referred to as a "bang." Maybe Paul can describe what he heard / felt when he had this issue. This has never happened in my plane, only cars and bikes. I can't help but wonder if it is something else.

Larry

If you've ever experienced an in-flight mag check where the pilot inadvertently shut off both ignitions then turned them back on, then you'll believe you can hear and feel a "bang" under the floorboards! Overly LOP (with mags) can also cause noticeably audible "pops" from the exhaust...
 
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If you've ever experienced an in-flight mag check where the pilot inadvertently shut off both ignitions then turned them back on, then you'll believe you can hear and feel a "bang" under the floorboards! Overly LOP (with mags) can also cause noticeably audible "pops" from the exhaust...

I would certainly expect turning off and on your ignition while spinning 2500 RPM would create quite a noticeable experience, though I have not done it in a plane. However, that is much more involved than "afterfires." The "Pops" you refer to are the explosions in the exhaust that we are referring to in this thread. I discussed above how an overly lean condition creates these "afterfires." I would expect them to be heard as pops like you describe. I would not expect them to be referred to as "bangs" that can be felt in your feet and make you wonder if something feel off your plane. As I mentioned, I have not experienced this in a plane and hoping others can describe the event so Brantel can determine if this is what he experienced and not something different.

Larry

Larry
 
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What I experienced was a very significant "pop" as I was leaning - not a sharp "bang" (as if someone hit aluminum), but clearly an ignition of fuel/air event. Finding the bad resistance and corroded plug wires was definitive to me.

Paul
 
You're not looking for a blown gasket, just a leak. A loose flange or missing chunk of gasket. During the exhaust stroke you get a strong volume of gas moving and it creates a negative pressure. A leaking gasket will allow air in which will cause any unburnt fuel to ignite (They started adding air into the exhaust in the 70's to combust remaining fuel in the exhaust to reduce the carbon emssions before they had FI to better manage AFR). Again, this shouldn't create enough energy to feel anything in your floorboards, just noise.

I still struggle to see how any combustion in the exhaust pipe could cause something you feel in the floorboards or creating something referred to as a "bang." Maybe Paul can describe what he heard / felt when he had this issue. This has never happened in my plane, only cars and bikes. I can't help but wonder if it is something else.

Larry

If you've ever experienced an in-flight mag check where the pilot inadvertently shut off both ignitions then turned them back on, then you'll believe you can hear and feel a "bang" under the floorboards! Overly LOP (with mags) can also cause noticeably audible "pops" from the exhaust...

I would certainly expect turning off and on your ignition while spinning 2500 RPM would create quite a noticeable experience, though I have not done it in a plane. However, that is much more involved than "afterfires." The "Pops" you refer to are the explosions in the exhaust that we are referring to in this thread. I discussed above how an overly lean condition creates these "afterfires." I would expect them to be heard as pops like you describe. I would not expect them to be referred to as "bangs" that can be felt in your feet and make you wonder if something feel off your plane. As I mentioned, I have not experienced this in a plane and hoping others can describe the event so Brantel can determine if this is what he experienced and not something different.

Larry

Larry

What I experienced was a very significant "pop" as I was leaning - not a sharp "bang" (as if someone hit aluminum), but clearly an ignition of fuel/air event. Finding the bad resistance and corroded plug wires was definitive to me.

Paul

The significant "Pops" I have experienced on the last 3 flights were very similar to the sound that airplanes sometimes make on the ground when being started and goes bang. I have heard this more with injected engines. Kinda like someone fired a 30-06 while laying in the prone position under the airplane. The only difference was I was non sitting on the ground and I was moving along at about 150 mph. The other occasional 'bumps" felt and sounded more like regular "misses".
 
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So here is where I am at this point:

Pulled all 4 rocker covers, rockers and springs from the exhaust valves. The E valves appear to be free and slick, I have not done the wobble test yet since I am waiting on the fixture tool to arrive next week. The clearance seems normal to me and others on the field with much experience.

I have pulled all 8 plugs and have inspected the edge of the E valves thru the top spark plug hole. #1 while it seems to be sealing all the way around, one spot makes me want to double check the valve head with a borescope. The other 3 look very much normal with what appears to be good seating. #1 is seating all the way around but one spot appears to be a bit thin.

I have ordered an articulating borescope to be able to check the valve faces that should arrive next week.

I used a hangar neighbor's straight borescope to inspect the top and edges of the pistons. They look normal to me with typical carbon buildup but no signs of other nastiness around the edges.

I have checked the tanks and the gascolator for water and I found absolutely nothing.

I have checked the plugs for issues.
The top car plugs are on the P-mag and look like a textbook example of a properly running plug. They ohmed out ~5K ohms each. These typically get replaced annually since they are so cheap.

The bottom plugs are regular massive plugs by Tempest. They have about 50 hours on them and they ohmed out at ~1K each. I did pick out some hard ceramic like crud from all 4 plugs around the center electrode/instulator

I inspected the Pmag wires and found that their resistance was very similar across the board and met the specs called out in the Pmag manual 450-550 ohms. There was one wire that has been being rubbed by something. A section about 3/4" long has rubbed away about 25% of the silicone insulation (will examine this more later). The Pmag wires where installed per the manual with spacers between them and very few places where the wires could cross talk. Not completely separated but as much as practicable. I checked the connections and they all look good since I always use dielectric grease.

The regular mag wires were inspected as well. The resistance in these was less than 2 ohms each. They looked to be in great shape. The springs and the silicone tips that the springs mount to looked OK. There was a little bit of black on them but nothing that looked too bad.

Before pulling the mag/Pmag I checked the timing and both were spot on.

The Pmag is getting shipped back to Brad for the Flat Fee Check-up since it needs the latest V40 firmware. The tattletale sticker has never turned black and the bearings seem good but I would like Brad's team to check it all out good.

I pulled the mag off and inspected it. There was one post of the distributor block/cap that has some significant smoky looking appearance to it kinda looks like carbon dust or evidence of arcing. (will inspect this more later) This is the post that receives the spring from the wire harness/outer cap. The other 3 post looked normal. The silicone ends of the wires had some black on them but nothing that looked too out of place. Springs looked normal.

The distributor block/cap looked OK inside with some gear train dusting but I did not see much if any evidence of arcing or carbon tracing.

The rest of the mag parts looked very normal. The mag has 350 hrs since the 500hr overhaul I did many years ago. At that time I replaced all the gears, rotor, the distributor block/cap, brush, cam and points. The points and cam also look normal. (Will check E gap later)

Tomorrow the exhaust and intake tubes come off for inspecting the gaskets for leaks. I have new ones to go back. I also have new intake tube hose couplings and clamps for extra insurance.

So far all I have found is the place rubbed in the Pmag plug wire and the evidence of arcing on the mag's distributor block post...

The saga continues! Any advice is definitely welcome!
 
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I thought more about your issue and you raise a good point that both plugs have to fail for the spark to be the cause of an afterfire and they likelihood of both stopping for one cycle on both igntion's is quite remote.. There is also the issue that it is very isolated. If your engine is FI, I would pull the injectors to clean. You can get a piece of trash or debris that only occassionally blocks the injector, causing a lean condition. That condition should have presented itself by showing random quick spikes (mostly down) on the EGT for one cylinder.

Larry
 
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I thought more about your issue and you raise a good point that both plugs have to fail for the spark to be the cause of an afterfire and they likelihood of both stopping for one cycle on both igntion's is quite remote.. There is also the issue that it is very isolated. If your engine is FI, I would pull the injectors to clean. You can get a piece of trash or debris that only occassionally blocks the injector, causing a lean condition.

Larry

It has a carb. # 10-3878 that has been drilled out to a #30 since the first 5 hours. Mahlon has mentioned that the 10-3878 was subject to a "M" kit modification to help solve some issues where people would experience occasional misses. I have examined the engine logs and see no indication of any change in EGT or MP on the engine logs. I have compared them to flights from a couple years ago and they seem to be similar.
 
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Ignition Switch?

I guess anything is possible but it has never acted strange whatsoever when doing mag checks. I may be over thinking it but one might think that if the switch did momentarily ground out both the Pmag and the Mag that you would feel the loss of power and that it would go for more than one cycle. I never felt any loss of power and the pops seem to be instantaneous events. I also see no indication of any change in EGT or MP on the engine logs.
 
Brian: Sounds like you have all the bases covered so nothing to add to your search, however my money is on a ignition problem. I would look at the mag distributor block with a bright light and a magnifying glass. Separate issue: since your exhaust rocker arms are out you should check that the correct bushings with the oil passage are installed. Put rocker shaft in rocker arm and blow some air in the pushrod socket oil hole and make sure it comes out the small hole on the opposite side. I've seen this installed wrong numerous times.

Don Broussard A&P/IA
RV9 Rebuild in Progress
57 Pacer
 
You may have found your culprit with that arc over.

I am thinking so as well.

Brian: Sounds like you have all the bases covered so nothing to add to your search, however my money is on a ignition problem. I would look at the mag distributor block with a bright light and a magnifying glass. Separate issue: since your exhaust rocker arms are out you should check that the correct bushings with the oil passage are installed. Put rocker shaft in rocker arm and blow some air in the pushrod socket oil hole and make sure it comes out the small hole on the opposite side. I've seen this installed wrong numerous times.

Don Broussard A&P/IA
RV9 Rebuild in Progress
57 Pacer

Will do on the Mag distributor block.

Thanks for the advice on the rocker arms. I am checking the rocker arms out as well. Believe it or not I think I found at least one cylinder where the engine builder installed them opposite of how they are suppose to be installed. I found the service instruction on how to ID them and that details which one goes where. This means that now I am not only chasing a weird issue, I am also cleaning up someone else's mistake. Will have to check the dry tappet pushrod clearance and hope that I can make the pushrods work out....
 
Brian I had a cracked distributor cap on my one mag that gave silimilar symptoms at high power settings. With one light speed ignition that has been totally reliable I tended to ignor the mag. It still contributes to performance and can also cause issues when maintenance is required
 
Brian I had a cracked distributor cap on my one mag that gave silimilar symptoms at high power settings. With one light speed ignition that has been totally reliable I tended to ignor the mag. It still contributes to performance and can also cause issues when maintenance is required

Good to know that similar symptoms can exist even though we both have two independent and dissimilar ignitions installed. This is really building a case for the distributor block/cap dusting that I have.

Will take pictures today and post later.
 
[Believe it or not I think I found at least one cylinder where the engine builder installed them opposite of how they are suppose to be installed]

I have seen this issue numerous times. It's easy to get this wrong on assembly and several other ways as well. If you had a exhaust rocker swapped with the intake be on the lookout for excessive exhaust valve guide wear on that cylinder. The lack of lube and cooling can accelerate wear especially on the right side cylinders. If you need pushrods I might have what you need.

Don Broussard
 
So rather than try to post all the pics here where they will eventually get deleted by the hosting company, I made a shared folder on my google drive.

Here are the photos and comments that I made on my findings once pulling the regular mag apart and inspecting it:

(CLICK IMAGE TO GO TO PHOTOS)


This details what I found on the distributor block/cap that looks like strong evidence of arcing on one of the four post.
 
Had this wobble test fixture tool 3D printed by Proto Labs DuraForm HST (Mineral Fiber Filled Nylon-12) Selective Laser Sintering.

They look awesome! Can't wait to try it out.

ogm.jpg
 
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Had this wobble test fixture tool 3D printed by Proto Labs DuraForm HST (Mineral Fiber Filled Nylon-12) Selective Laser Sintering.

They look awesome! Can't wait to try it out.

OOB
I shake my head at you <with a smile>.
 
After evaluating all the options of:

Overhauling the Mag myself (I don't have the tools to do a full teardown and inspection and the piece parts can easily exceed the cost of a new unit)
Getting a Mag shop to overhaul the Mag (they typically only replace what looks worn out or checks bad which means that the coil and condenser are typically not changed)
Purchasing an overhauled Mag (they typically only replace what looks worn out or checks bad which means that the coil and condenser are typically not changed)
Purchasing a rebuilt Mag (they replace all wear items, coil and condenser)

Due to the cost of the above options and the limited service life (my experience others may vary) of those things I have decided to divorce the antique technology completely and replace it with another more modern electronic ignition. I really have no idea how many hours are on the existing impulse coupling and I don't want that thing coming apart inside my engine.

While I struggled with the pros and cons, I have decided to add a second Pmag instead of using one of the other EI systems available.

Most contributing pros are:

1. I already have an existing Pmag that has worked as advertised.
2. I would really like to have the advance curves match on both ignitions and the only way to really do this for for them to be the same make/model and run the same settings.
3. I can do some limited customization of the advance curve to tweak it to my liking.
4. The fact that the Pmag has a built in power backup scheme makes it easiest to install for me without requiring a backup battery.
5. It can use car plugs and wires. The existing ones look beautiful each time I check them.


If I had not already been in bed with the existing Pmag, I would most likely install a dual SDS CPI. That looks like a sweet system for the money.
 
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So tonight I used the SB 388C "wobble test" tools I had 3D printed and you can read about how they worked and some issues I found with Lycoming's design here in this thread:

http://www.vansairforce.com/community/showthread.php?p=1195412#post1195412

Here are the results of my testing the wobble of my exhaust valves after correcting the readings for the geometry error on Lycoming's part:

Uncorrected:
#1 = 0.020"
#2 = 0.0275"
#3 = 0.023"
#4 = 0.027"

Corrected:
#1 = 0.016"
#2 = 0.022"
#3 = 0.0185"
#4 = 0.022"

Lycoming allows from 0.015 to 0.030"

I went ahead and ran the reamer thru #1 just to ensure it was clean. Will retest as soon as I get the valve back in the guide.... :(

Update: after reaming #1, it measured the same. Hardly any crud came out with the reamer.

The geometry behind the correction:

emBivM5.jpg
 
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Since I am knee deep in the engine at this point, I figured it would be a good idea to inspect the valve faces with a borescope and followed the recommendations on other threads and picked up a Vividia AbleScope VA-800 USB Flexible Inspection Camera:

s902975211958334_p280_i2_w800.png



This thing works like a dream!

I inspected the edges and faces of all 4 pistons just to ensure nothing weird was going on with them. All was good.

Then I used the articulation feature to get a good look at all the valves.
Here are the results:

CLICK PIC BELOW TO SEE IMAGES IN MY ALBUM:



I assume the lead deposits are because I have a carb and can't run LOP very well and I use 100LL all the time. I don't know much about how to interpret these images other than to look for symmetry which I think I have. I also don't see any green which I understand is good.
 
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Yes, the valves look good. I take pics of mine every 6 months or so and name the files by cylinder and date before archiving. Problems most often occur on the exhaust valves (smaller of the two) rather than the intake valves You can also position the prop just right and then rotate it back and forth just enough to observe the valve seat and unseat, watching whether the alignment is good. A good diagnostic for when the valve guides need work.

Erich
 
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After evaluating all the options of:

Overhauling the Mag myself (I don't have the tools to do a full teardown and inspection and the piece parts can easily exceed the cost of a new unit)
Getting a Mag shop to overhaul the Mag (they typically only replace what looks worn out or checks bad which means that the coil and condenser are typically not changed)
Purchasing an overhauled Mag (they typically only replace what looks worn out or checks bad which means that the coil and condenser are typically not changed)
Purchasing a rebuilt Mag (they replace all wear items, coil and condenser)

Due to the cost of the above options and the limited service life (my experience others may vary) of those things I have decided to divorce the antique technology completely and replace it with another more modern electronic ignition. I really have no idea how many hours are on the existing impulse coupling and I don't want that thing coming apart inside my engine.

While I struggled with the pros and cons, I have decided to add a second Pmag instead of using one of the other EI systems available.

Most contributing pros are:

1. I already have an existing Pmag that has worked as advertised.
2. I would really like to have the advance curves match on both ignitions and the only way to really do this for for them to be the same make/model and run the same settings.
3. I can do some limited customization of the advance curve to tweak it to my liking.
4. The fact that the Pmag has a built in power backup scheme makes it easiest to install for me without requiring a backup battery.
5. It can use car plugs and wires. The existing ones look beautiful each time I check them.


If I had not already been in bed with the existing Pmag, I would most likely install a dual SDS CPI. That looks like a sweet system for the money.

So I sent my original Pmag into EmagAir to let Brad's team check it out good to ensure it was doing well. It had 260hrs on it so it was a bit premature to have a checkup but I decided since I had it off and wanted to rule it out as being the culprit of my issues and it needed the latest firmware update, I went ahead and bit the bullet and used their flat rate checkup service.

They tore it down, inspected, found nothing amiss and updated the firmware and sent it back with their version of a yellow tag so I am good to go with that one. Thanks Brad and team!

The second new Pmag is in hand and I have already updated the wiring in the plane to be ready to pop that sucker in. I have removed the old impulse coupled mag spacer and replaced the studs with shorter ones.

I also decided to add Bill's EI Commander to my panel. While I have already cracked the code on how to build a monitor for the Pmag's, I would have to make one that is in a nice package and panel mountable and Bill has already done that. To be honest, I don't have time to spend on making my own so Bill got an order. I already had a 2.25" spare hole with a blank in it. Worked out perfectly for the EIC. I do not plan to use the EIC to make timing changes in flight, only to make tweaks to the config on the ground and to monitor the 2 Pmags to keep and eye on them. The EIC and all wiring has been installed and tested.

To be honest with the work that Nigel did and the fact that I have never been very successful running LOP with my carbed engine, I am seriously thinking about shifting/limiting the Pmag's curve to the point that they run basically fixed timing. For me the advantages are not in timing advance but in the easy starting and car plugs and getting that impulse coupler out of my engine before it decides to explode.

Waiting on new pushrods to button up the top end. New silicone rocker cover gaskets standing by. The oil drain, intake and exhaust tubes are going back on tonight. New gaskets, new oil drain & new intake tube hoses going on as well to eliminate any leaks that may have been hiding there.
 
The oil drain, intake and exhaust tubes are going back on tonight. New gaskets, new oil drain & new intake tube hoses going on as well to eliminate any leaks that may have been hiding there.

Throw away the slotted hose clamps.
 
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I did use slotted hose clamps. Due to access, they are very easy to install and inspect tightness later if needed.

But I used full circle (even pull) hose clamps from NAPA Auto parts.
 
From an old post:



An excellent example of why we should never use band clamps with slots. Much of the original clamp pressure bled away when the rubber extruded through the slots. Use solid band screw clamps with embossed slots (look up ABA brand clamps at Wicks), or screw clamps with solid liners (see Breeze liner clamps at Spruce), or constant pressure spring clamps (like Brian posted, or below).

From Kitplanes...

The most popular OEM choice sidesteps the entire loss-of-clamping issue. Spring clamps (Fig14) are “constant clamping”, meaning even if the rubber extrudes or shrinks, the clamp will contract and maintain sealing pressure. They work well with all medium to soft rubber compounds (including silicone), are lightweight, and require little space. They can’t wear out, so this kind of clamp can also be very economical - OEM clamps salvaged from late model import cars will be as good as any you can buy.

aelc04.jpg
 
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Clamps

Yes sir...

Good Man!
I have ordered all the new hoses and spring clamps for drainback and intake per a previous post but haven't done the work yet. Sure seems like a great idea to help stop the seeps. I personally think it will look more professional as well.

Thanks Dan for posting the pics.
 
A buddy brought his new Chevy SS by for a look this afternoon. Naturally I popped the hood to look at the hose clamps ;)



Heck, they don't even use slotted clamps on the air ducts any more. These have embossed teeth on the bands.

 
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