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O360 A4M spark plug damage.

Wrench

Member
Looking for some input...

Piper Archer III, ( please don't flame me :), .. with an O360 A4M with 800 hours since new. I am the original owner. Plane has been very reliable. One vacuume pump and an alternator are all that's been replaced. Mags overhauled at 500 hours, plugs at 400 and recently at 750.

Fired her up yesterday..all temps/pressures in the green. Run up and mag drop were fine. Rolled out on the runway.. everything was good till I was about a foot in the air when the engine sagged real bad. Put her back down and taxied back to the ramp. Acted like a fouled / bad plug... but she would not clear up. She was really shaking.... whew !

Pulled plugs... all were in excellent shape except #4 cylinder. " Ugly " pictures attached. Melted electrodes on top #4... bottom #4 same with the addition of busted ceramic insulator.
Had to get back home.. so other than looking to make sure the piston was still going up and down, this was the extent of my inspection...but heading back in a couple days.

Plan is to..
> Borescope cylinder
> Pull rocker cover and have a look
> Inspect intake tube for air leaks
> Check timing

This all happened in less than 15 minutes from start up to shutdown... strange to me... but maybe some of you guys can add some sanity to this.

Will have my A/P get involved but he is tied up for a couple weeks so I'm just wanting to get a bit of a head start.

Any input appreciated - Thanks !
 

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Plugs

My thought is that you will find evidence on the top of the piston of something bouncing around inside the cylinder.
I would not describe the spark plugs as welded but rather mechanically damaged by foreign object.
Make sure to check you entire induction, air filter and carb heat.
 
Carefully check the air filter and ducting for loose or lost fasteners or rivets.
I had a pulled rivet get sucked thru a cylinder once, it did similar damage to the plug with no other visible damage.
That cylinder did have to be rebuilt 5 hours later for a bad valve...
 
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Yea me thinks you have or had something bashing things around in #4.
Don't see any melting here.
Need to get a borescope in there pronto.
Probably gonna find a few dings in the piston and ?????.
Art
 
I agree.. something went through there, perhaps a screw or rivet or a washer.. something banged around in there. The top of the piston should be a clue.
 
Ha Ha after posting a bit ago I was thinking of a time about 50 years ago I had a hot rod and I guess I was concerned about loosing the key.
You know how young boys are when they party and all.
Well, I stored an extra key in the air cleaner.
As luck would have it, it was delivered to the cylinders via one of the three carbs.
It made one @^#%^ of a racket.
That 427 Ford tri power just chomped that brass key into little bits.
Put it in my shop and pulled the heads to find key parts in ALL the cylinders.
Fun Fun Fun Art
 
My thought is that you will find evidence on the top of the piston of something bouncing around inside the cylinder.
I would not describe the spark plugs as welded but rather mechanically damaged by foreign object.
Make sure to check you entire induction, air filter and carb heat.

UPDATE: Was able to get into the issue today.You guys were correct.... FOD.

Borescope was " unremarkable ". Intake runners were tight, valve train just fine...

The root cause appears to be the broken ceramic insulator on the bottom plug. It was the cause ...not a casualty of something else. Theory is... Insulator failed, bounced around as it was " consumed /spit out " in the combustion process.

Installed new plugs and ran her at idle a few minutes. Let her cool down and pulled the plugs for a look see. All was good...

.. did several high speed taxi tests.... let her cool and pulled plugs again... all looked good. Will put a couple more hours on her close to the airport ... then have one last look with the borescope.

Hard to explain the failed insulator, ( Tempest UREM37BY )... but all indications point to that.

Thanks for all you gets suggestions - I appreciate that !
 
Why you never use a plug after being dropped or use a “repurposed” implement to remove Pb deposits. You probably know this and probably took the appropriate care. it’s about the things we don’t see.

Stay safe.
 
Just one of many possibilities.

There has been a bulletin on using glass bead blasting for cleaning the plugs. It stated that a bead can get lodged between the electrode and insulator to fail it as noted here.

VW's used to eat the accelerator nozzles (brass), and one model had close piston/head clearance where it pinched a top ring. 99% just ate them and moved on.
 
Not a fan of the 37BY for this reason, I've seen a number of broken insulators with missing pieces over the years.
(never seen any damage caused by the missing pieces though)
 
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NO WAY that a piece of ceramic did this type of damage. Broken insulator is an effect, not a cause here. Note the small chunks of steel eaten out of the center electode as well as the small blobs of steel or aluminum that were likely molten before sticking to the steel parts. Looks a lot more like severe detonation or possibly pre-igniton to me.

Have you looked at the top of the piston yet?

I could buy a piece of steel being injested and bounced around, but ceramic bits wont chew up steel like that.

Larry
 
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I'm not sure if this in the exact document Bill is referring too, but it mentions what he is talking about and has much more info on cleaning our plugs properly. It's worth the read.

Tempest pdf document, here

Thanks,

Joe

For the last 24-years, I have used nothing but a vibratory cleaner like shown in figure 11 in the linked document on spark plugs.
 
Borescope was " unremarkable ". Intake runners were tight, valve train just fine...
+1 on Larry‘s post above. I wouldn’t be that sure the problem‘s been solved, those spark plugs look horrible, and the ceramic insulation being friable as it is, is unlikely to have been the source… FOD yes, insulation questionable.

If it were mine, I’d redo a detailed borescope, compression, oil change/filter/analysis, and then reassess.
 
+1 on Larry‘s post above. I wouldn’t be that sure the problem‘s been solved, those spark plugs look horrible, and the ceramic insulation being friable as it is, is unlikely to have been the source… FOD yes, insulation questionable.

If it were mine, I’d redo a detailed borescope, compression, oil change/filter/analysis, and then reassess.

Update: ... did a " deep dive "... You guys were spot on...a 1/4" nut was found laying at the base of the #4 intake tube...it was beat up... top of piston and cylinder head were full of " tiny pings "..

How the nut got there is a mystery so far. Nothing has been disturbed since the last annual over 100 hours ago. I can't find any missing nuts either..

Is it possible to suck a 1/4" nut from the " carb heat side " of the air box up through the carb.. through the intake runner and into the engine ? On my plane the airbox has the wire mesh screen between the exhaust pipe and carb but has an additional hole that has no screen and is also open to the elements when carb heat is applied. Anything that gets in that area is going to be sucked into the carb. One thing for sure.... the nut got into the cylinder... still looking into how..

Cylinder has been pulled.... replacement on the way. Pulling all intake tubes while were in there to have a look see.
 
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