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Multiple Spark plugs damaged

K

Kevin M

I'm New Here
I have about 400 hours on a completely rebuilt O-320-D2A that has had something crush the grounding strap closed on three different spark plugs in the last 3-4 hours.NGK-BR8ES first 2 times running with 2 Emags. This has happen on two different cylinders both the back cylinders 3 once & 4 twice, all times lower plugs in a RV9A. When rebuilt at a known shop in Colorado a new crank, cam, nitrated steel cylinders and fuel injection was installed. I put almost 300 hrs with no issues, then3-4 hours ago when flying engine stumbled then flew normal. However next flight when doing a mag check it ran bad, #3 egt dropped back when left mag was shut off. Pulled plug and found the ground strap on spark plug crushed down flat touching center electrode. Using an end scope top of piston showed carbon build up but no damage, valves looked good and compression check was good mid 70's. Put a new plug in and engine ran good for about ¾ hour when engine stumbled on climb out at neighboring airport but ran good going home but on the ground before shut down check mags and # 4 cylinder showed bad when right mag shut off. Pulled spark plug and ground strap was bent down maybe with a .004 gap. End scope showed carbon build up more oily than the first cylinder but no damage. These plugs were less than a year old with maybe 70 hours on them, originally set to .035. I called the Emag factory and they were very helpful and while not knowing what caused the damage after telling tell about the carbon buildup on the top of the piston thought it was possible a chunk came off hitting the grounding strap of the plug bending it. They recommend I try one step hotter plugs NGK-BR7ES which I changed all 8 to those. Start up and mag checks good but on the first climb out at full rich at 1000agl engine stumbled bad but after 1-2 seconds came back and ran good while I immediately made a normal landing. #4 cylinder lower sparkplug crushed down to .010. Engine was setup for Colorado at 5000 MSL where I am at 1000 msl maybe altitude makes a difference? I do get more that 50 rpm increase when going from full rich to shut down but thought that if I lean hard on ground it would not matter. I thought that idle mixture setting had nothing to do with cruse setting especially when I manually lean at altitude.

I always run lean on the ground and lean of peak at cruise but full rich while climbing. I am burning around 12-13 gal/hr while full throttle at full rich. I do have a fix pitch prop so during climb out I get only 2100-2200 for a while until leveling out. I typically fly lower power 60% or so at 2200 rpm but lean of peak. The previous owner told me he had trouble holding CHT down during breaking in the new overhaul so maybe the cylinder are glazed. I didn't think oil burn was that bad at 1qt per 20-25 hours but I have not kept good records on that. Maybe my oil ring or rings are stuck and I should try the oil control ring solvent flush to loosen them up? Maybe a oil ring has broke, and chucks are coming up and then hitting the spark plugs? Maybe as a last resort my AP/IA will have to pull the cylinders to check them out?

See pictures
In the top view of the plug you can see where something hit the grounding strap at the very end of it.

Any thoughts ?

Thanks for any help

Kevin
 

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gasman said:
Scope a cylinder with a plug installed. There should be no threads extending into the chamber.

It looks to me, like a long reach plug in your photo.
Click to expand...

BR8ES is an auto plug. It'll be the adaptor, not the plug itself.

Kevin, are you using SR or LR plug thread adaptors? Your O-320-D2A engine needs SR, I'm going to guess you're using LR, and the face of the piston is smashing into the bottom of the spark plugs.

- mark
 
newt said:
BR8ES is an auto plug. It'll be the adaptor, not the plug itself.

Kevin, are you using SR or LR plug thread adaptors? Your O-320-D2A engine needs SR, I'm going to guess you're using LR, and the face of the piston is smashing into the bottom of the spark plugs.

- mark
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LR plugs (Denso IKH27, mine) have 17 threads, I don't these have that many.....
 
newt said:
BR8ES is an auto plug. It'll be the adaptor, not the plug itself.

Kevin, are you using SR or LR plug thread adaptors? Your O-320-D2A engine needs SR, I'm going to guess you're using LR, and the face of the piston is smashing into the bottom of the spark plugs.

- mark
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I think Gasman and Mark nailed it. Kevin- in your last picture it most definitely looks like your plug is getting smacked by the piston. Those plugs are not doing you any favors because they can’t give you the spark you need. The good news is this may be a pretty easy fix just by swapping to the shorter SR plugs.
 
The BR8ES is the correct plug, if it was in a LR adapter it would not extend out of the adapter (adapter is longer than the plug).
I would look at how far up the piston is coming in the cylinder, were the pistons or connecting rods replaced?
 
georgemohr said:
And if its the pistons, why would there by any variance in the stroke at all? This is puzzling...
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That was my thought as well. If this was truly an interference between the piston and the plug, you'd see it as soon as the engine was running.
 
A picture of the plug in the adapter would be nice, I'm not actually sure of the normal piston/spark plug clearance.
I have seen adapters installed without the copper gasket, they are pretty thick so certainly would reduce the clearance if missing.
 
olyolson said:
I think Gasman and Mark nailed it. Kevin- in your last picture it most definitely looks like your plug is getting smacked by the piston. Those plugs are not doing you any favors because they can’t give you the spark you need. The good news is this may be a pretty easy fix just by swapping to the shorter SR plugs.
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If using PMAGS, the BR8 plugs are the preferred and recommended plug. I was originally using BR9's because I had a bunch of them sitting around for snowmobiles but was ultimately persuaded by Emag and here on VAF that I should be running plugs just a bit hotter in my PMAG-equipped airplane.

I've never had any plug damage on my IO320 D1A using those automotive plugs with short reach adapters.
 
Snowflake said:
That was my thought as well. If this was truly an interference between the piston and the plug, you'd see it as soon as the engine was running.
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Puzzling, for sure. But this has me wondering if thermal expansion, making the piston taller as well as wider, could account for piston/electrode contact at 45 minutes of operating time versus immediately on startup.
 
Thanks for all the replies, I will try to answer some of the question or comments.

I agree if some parts came loose inside the airbox they could get sucked into the cylinder bounce around until expelled out the exhaust valve. I will check that out.

Plugs are what Emag recommends and what I have been using for the last 3 years except last flight when I went to the hotter BR7ES plugs.

Yes I use the brass thread adapters with a cooper washer under adapter torquing to 18 foot lbs on the plug only.

I will post a picture of the plug in the adapter, I don't know if their long or short but there the sames ones for the last 3 years.

Temperature wise my CHT are around 325 -350 in cruise and I have to climb hard to get to 400 but I rarely see that as my Skyview warns me at 395. EGTs usually under 1300 when lean on ground or cruising but can go over 1300 when starting to lean as I go past the peak going down as I lean. I don't think I have every seen anything over 1350.

Thanks again for all the replies I really appreciate it.

Kevin
 
Walt said:
I have seen adapters installed without the copper gasket, they are pretty thick so certainly would reduce the clearance if missing
Click to expand...
Something changed, so maybe. As well as the long reach plugs being installed. Easy to check and rectify.
 
I have used NGK BR8EIX iridium plugs for 11 years without issues on my dual p-mag o-320. These plugs are the same 19mm reach as the BR8ES plugs in question. I lean towards an issue with the adapters and/or missing spark plug copper gaskets on the affected cylinders. You might compare the adapters with the 1 & 2 cylinder adapters or even swap them to see if the problem follows the adapters. Install new copper gaskets. I always anneal the gaskets and the flat side of the gasket goes against the plug, but not doing so wouldn't cause this problem.
 
Any clearance issues between spark plug and piston would be noticed when pulling the propeller through 1 - 2 complete revolutions. Not after 70 hours or a run up or whatever.

However, do confirm that each piston is the same: pull the top plugs, insert a wooden dowel in the plug hole, then pull the prop through TDC for each cylinder, measure the height (depth) of the dowel on each cylinder at TDC. The measurement should be the same for each; if not, then it's possible that the shop put higher compression pistons in a couple of the cylinders (!!!)

Are you sure you just didn't drop the plug and bend the cathode?

edit: As to some "trash" banging around in the top of the cylinder head - insert a borescope through a spark plug hole and inspect the entire volume of the cylinder, reflex and look at the valves also.

G/L

B
 
So, the $1000 question is what changed? You put 300 trouble free hours on that engine after being built and all of a sudden in two flights, two spark plugs have their electrode bent. It can't realistically be a clearance issue with the piston, as you can't really have things moving around like that inside the cylinder. The clearnace between the piston crown and sparkplug is not small and if the piston or rod were loose, it would have grenaded by now. If something big enough to bend that electrode were bouncing around in the cylinders, you should see plenty of evidence of it via large chunks broken out of the carbon on the piston crown in addition to the head and crown surface showing serious poc marking.

So, what changed just before this event? I suspect that will be your biggest clue.

Larry
 
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Weird.

So the OP confirms the right adapter (short reach) and right plug (BR8ES) is being used (same for all parallel valve Lycomings). But the evidence also confirms the piston is striking the bottom of the plug.

As this has not happened in the the previouts 300 hours we can assume something has changed.

Two pieces of data that are unknown is does this engine have high compression pistons? Are you using both the copper gasket under the plug adapter and the lock washer under the plug (between the plug base and the adapter)?

I recommend some careful measurements of piston stroke using a feeler gauge in the plug holes. Compare the bad cylinders with the good ones. What story does this say?

While I don’t recommend just addressing the symptom, you could put two copper gaskets under the plug adapters in the effective cylinders. I would not fly that way as this could be the opening salvo of something bad starting to happen.

Carl
 
Carl Froehlich said:
Weird.

But the evidence also confirms the piston is striking the bottom of the plug.

Carl
Click to expand...

Where is that evidence? I saw nothing in those 4 pics that confirmed that. Yes, a couple areas are carbon free, but we have no idea if that is where the plug is. If anything, the small dimple on the end of one of the ground strap confirms that it WAS NOT the piston that hit it, but something with a relatively sharp edge.
 
Compare an old plug against a new one. Years ago, after a change of plugs on a 182, it seemed that the ignition wires were bent into a 90 deg turn harder than before. Comparing old vs new plugs (Champion, same exact designation) it seems Champion had simply started manufacturing slightly taller plugs. No warning.
 
Thanks for the replies

Yes I do have high compression pistons 9.25 to 1.

Yes I do use a new copper washer under the bushing new every year when I change plugs but did not know there was different sides, I better look into that. I keep the compression washer on the spark plug and gap at .035.

I am sure I did not drop any spark plugs. :)

Just his noon I had a pilot stop in and say he had seen something like this before on a different engine. Part of a snifter valve for a manifold pressure sensor had broke off and was bouncing into the cylinder and then back down the intake pipe to the intake manifold only to be sucked up into another cylinder later. I will scope and pull the intake tube off the last cylinder that had the damage spark plug and try to look in the intake manifold.

I will post later a picture of what he found in that engine not mine.

Thanks
Kevin
 
Kevin M said:
Just his noon I had a pilot stop in and say he had seen something like this before on a different engine. Part of a snifter valve for a manifold pressure sensor had broke off and was bouncing into the cylinder and then back down the intake pipe to the intake manifold only to be sucked up into another cylinder later. I will scope and pull the intake tube off the last cylinder that had the damage spark plug and try to look in the intake manifold.
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This sounds like the most likely explanation I've heard so far. Very interesting problem.
 
I had a similar experience.

My FAB kit came with some stainless steel anti rotation clips that were used on the 4 bolts that secured the FAB plate to the carburetor. On my to do list was to drill the head of the bolts so I could use safety wire and toss the clips. Unfortunately, I kept on pushing out that task. I'm assuming that the clip broke because one of the bolts backed out (found it in the FAB) and the light clip was sucked into the induction system. It found it's way to the #1 cylinder where it bounced around, bent the grounding strap closed killing my NGK BR8ES plug. This occurred during takeoff.

Below is a picture of one of the clips. One of the valves got nicked. I ended up overhauling the cylinder.
1716508567613.png
 
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Well I think I have found my problem. I removed #4 intake pipe the last cylinder that had a damaged spark plug and found a screw off my alternate air valve door assembly. Walt & drill & buck were right. I did not know that FOD material could get pull up and fall down back into the intake pipe or manifold then cross over to another cylinder.

Thanks for the comments and help

Kevin
 

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Amazing, glad you found this potentially catastrophic issue.

PS: on the 14, this door ring is riveted to the intake plenum. Probably a better approach for this reason.
 
Great job finding the issue Kevin! Hopefully no further action is required and no damage to the engine. Looking at your pictures of the alternate air door George makes a good point about using rivets instead of screws and nuts to hold the alternate air door ring. You want to make sure this doesn’t happen again with one of the other screws/nuts. May not be a bad idea to take the air box off, remove the ring and reglass the ring opening then attach the door ring with rivets. While you’re at it a really nice addition would be a better alternate air door mechanism available from Aircraft Specialty Flightlines. I have never really been happy with the standard alt air door mechanism from Vans and mine never did move very smoothly. I just installed this one and it is smooth as butter either opening or closing, no binding just silky smooth now.

Here’s the link: https://aircraftspecialty.com/altairdoor.html

IMG_1404.jpeg
 
This is one of the reasons I don't like seeing alt air doors on Carb engines. The risk/reward ratio is off.
A) effort & time to put in the door
B) Typical carb equipped certified planes don't have a door
C) anything that departs the door can (confirmed!) go up the engine. When hard objects go up the engine bad things can happen. A shorted spark plug being one of the least bad.

To be fair, what's the reward? Well, maybe if you take a lot of wet snow? So, engage carb heat BEFORE and make the carb heat door seal properly in the on position. Maybe you take a bird, fod, etc. and it plugs the chin inlet? With alt air you need to recognize and pull the actuator. With carb heat, same, but there's a possible chance the FOD has also blocked the carb heat. There is the risk.

Plus the doors leak and so you don't get as much positive air pressure from the ram system.
And they open up letting dirt into the engine.

So my contrary vote is: don't throw more money at it. Get rid of it.
 
There are lots of prior discussions on VAF about Alt. Air doors. Many of us chose not to install them as there had been more than a few instances similar to the OP and a close to zero known instances where having an Alt. Air source saved someone’s butt.
Looks like there are some better engineered solutions out there for those that have to have one.
 
One thing doesn't make sense.
blaplante said:
maybe if you take a lot of wet snow?
Click to expand...
Years ago, an airline pilot flew his carb'd RV-6 into a snowstorm at night near Tehachapi which NTSB thinks clogged the air filter with snow. The heated alternate air system did nothing as it ducts in hot air UPstream of the filter, so with a clogged filter, no clearing of the snow was possible. After this crash is when Van's released their retrofit bypass air valve kits which duct in air downstream of the filter. I met the pilot an hour before he and his girlfriend perished. Still a bit eerie.

The problem is not understanding how the stock heated alternate air system works and failing to turn it on before the filter clogs with snow. For a guy like blaplante the bypass is obviously not necessary.
 
hgerhardt said:
One thing doesn't make sense.

Years ago, an airline pilot flew his carb'd RV-6 into a snowstorm at night near Tehachapi which NTSB thinks clogged the air filter with snow. The heated alternate air system did nothing as it ducts in hot air UPstream of the filter, so with a clogged filter, no clearing of the snow was possible. After this crash is when Van's released their retrofit bypass air valve kits which duct in air downstream of the filter. I met the pilot an hour before he and his girlfriend perished. Still a bit eerie.

The problem is not understanding how the stock heated alternate air system works and failing to turn it on before the filter clogs with snow. For a guy like blaplante the bypass is obviously not necessary.
Click to expand...
That story from many years ago to this day affects my flight planning, and yes, your chance meeting would spook anyone.
 
blaplante said:
This is one of the reasons I don't like seeing alt air doors on Carb engines. The risk/reward ratio is off.

So my contrary vote is: don't throw more money at it. Get rid of it.
Click to expand...
Totally agree - it's an example of an unnecessary, unneeded complication. New approach.. instead of trying to think of every possible thing to add, make the game trying to create as simple and reliable an airplane as possible, ie, aim for "less is more". It's a fun and far more interesting game. Keep these simple little airplanes simple!
 
71459 said:
Totally agree - it's an example of an unnecessary, unneeded complication. New approach.. instead of trying to think of every possible thing to add, make the game trying to create as simple and reliable an airplane as possible, ie, aim for "less is more". It's a fun and far more interesting game. Keep these simple little airplanes simple!
Click to expand...
Many RV6's were completed in the 900# range because they were built to Van's instructions. The Bloating was started by builders.
 
That accident was in 2001 https://www.ntsb.gov/Pages/ResultsV2.aspx?queryId=b4b9e6a8-0f9e-4629-a472-f657a6463c78
Those early carb heat installs used a very small area muff, and the door did not seal up the inlet.
As a result people were seeing very little drop in RPM when pulling carb heat on runup. I think you can find that in the archives here....
I've seen installs where there wasn't any carb heat muff installed(!) - just pulling air from the lower cowl. [And the plane has been signed off by A&P inspectors for multiple CI's.]
 
blaplante said:
I've seen installs where there wasn't any carb heat muff installed(!) - just pulling air from the lower cowl. [And the plane has been signed off by A&P inspectors for multiple CI's.]
Click to expand...
Some may regard that type of "carb heat" to be insufficient but an A&P has no grounds to refuse the inspection since this is legal for an aircraft with an experimental airworthiness certificate.
 
That is amazing. The hole enlarged in the alt air door frame and it sucked the whole thing in. Is that a beat up fiber lock nut on the end of that screw ?

+1 to the suggestion to deal with the rest of them so it doesn't happen again. In your 3rd picture that one at the 11:00 position looks like it could do the same thing with a little motivation.

I know it's Monday morning quarterbacking here, but I used rivets and epoxy flox to hold the frame on. I first riveted a nut plate onto the back side of the frame for the screw that the door pivots on to screw into, then drilled a hole in the snorkel for the threaded portion of that nut plate and the tail of the screw to stick through. Then I epoxied the frame onto the snorkel with an epoxy flox mix. Once it had dried I drilled through the hardened epoxy at the rivet locations and squeezed flush rivets in. The only things on the inside of my snorkel are 6 rivet tails and the threaded end of the pivot screw. I challenge Murphy to find a way to make something go wrong with that setup.

Thanks so much for coming back here with your root cause!
 
@Kevin M glad to see you found the root cause. With the knowledge that the FOD was bouncing around in the cylinder and then exited via the intake valve, it would be a good idea to borescope the underside of the valves and cylinder dome and look for dings and scratches.
 
Desert Rat yes that is a fiber nut on the bottom of the screw. drill_and _buck that is a good idea to bore scope everything and I did the best I could but could not see the valves with my cheap borescope. I am in the process of fixing my airbox and reinstalling my intake tubes, I removed #3 as well because that cylinder had a spark plug damaged but I found nothing. I am not sure but that screw seem smaller that the rest. Hopefully I can fly soon and I will report back.

Kevin
 
blaplante said:
I've seen installs where there wasn't any carb heat muff installed(!) - just pulling air from the lower cowl. [And the plane has been signed off by A&P inspectors for multiple CI's.]
Click to expand...
Yes I have seen many RV’s set up this way. Air from the lower cowl is much higher temp than outside air and must work as we have not heard of issues over the last 15 years or so.
 
Steve Iacoviello said:
Yes I have seen many RV’s set up this way. Air from the lower cowl is much higher temp than outside air and must work as we have not heard of issues over the last 15 years or so.
Click to expand...
The rpm drop on that setup is usually barely detectable. Much less than what is seen on typical Cessna or Piper. Good enough? I don't know, but I have my opinion that less isn't better in this case.

In any case, the thread is about an Alt Air Door, we should probably stop the drift into Carb Heat design :)
 
May I ask what is the over/under on benefit derived from an alternate air door on fuel-injected engines? I have one in the -10, don't recall exactly how I executed the hardware retention during the build but I will pay attention to that when the airbox is apart for C.I. I know that the instructions said once pulled, it would be necessary too land and de-cowl to ensure the alternate air was reset to its closed position correctly. Is it worth keeping, once installed?
 
Bill Boyd said:
May I ask what is the over/under on benefit derived from an alternate air door on fuel-injected engines? I have one in the -10, don't recall exactly how I executed the hardware retention during the build but I will pay attention to that when the airbox is apart for C.I. I know that the instructions said once pulled, it would be necessary too land and de-cowl to ensure the alternate air was reset to its closed position correctly. Is it worth keeping, once installed?
Click to expand...
IMHO there is no difference carb or FI. You are either concerned that a filter could become blocked or you are not. In the former, you put in an alternate source that bypasses the filter and in the latter you follow your confidence/faith that the filter will not become blocked and therefore no need for alternate source. Pretty binary. Carb heat is upstream from the filter, so irrelevant to this discussion. If you feel the only source of blockage is ICE then MAYBE there is a difference, assuming you have tested the fact that carb heat volume is adequate to fully thaw a frozen filter. My $ says it is NOT, but doubt anyone really knows.

My biggest fear is sucking up a plastic grocery bag on take off. Ice aloft I can deal with in glider mode. engine dying at 100 AGL has low survivability. My recommendation is that every plane should have one. No different than someone removing a fire ext from the plane due to the risk of it coming off its mount and hitting the pilot in turbulence. Nothing is risk free, and we must weigh the pros and cons.

Larry
 
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blaplante said:
The rpm drop on that setup is usually barely detectable. Much less than what is seen on typical Cessna or Piper. Good enough? I don't know, but I have my opinion that less isn't better in this case.
Click to expand...
The Robbinswings muff I installed in my -6 (O-320 E2D) consistently gives me a noticable drop at run-up, 40-50rpm. I've used it to remove carb ice as well. It happens, even on a Lycoming, here in the Pacific Northwet.
 
Walt said:
A picture of the plug in the adapter would be nice, I'm not actually sure of the normal piston/spark plug clearance.
I have seen adapters installed without the copper gasket, they are pretty thick so certainly would reduce the clearance if missing.
Click to expand...
This would have been my thoughts if I would have read this blog sooner. I have forgotten a washer once upon a time. But, seen it in my work tray so went back and found the problem before it caused any problem. Stuff happens all the time.
I had a 64 ford falcon with a 427 hotrod motor a long time ago. Thought it would be a good idea to "hide" a key in the air cleaner. Good idea "right??"
Wrong!!!! it got into the intake manifold, then the cylinders. yes chomped up into three cylinders. After both heads off to clean it out. there were three plugs smashed just like the ops.
My luck varies FIXIT
 
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