Stump The Mechanic - An Obvious Tune Up Issue With No Obvious Causes

There are lots of things that can damage a spark plug in a running engine, but in the case of this particular one, none of the usual suspects apply.
We found reason for our cars lackluster performance at the drag strip this last Saturday night, but after running through all of the possible causes, we're stumped for an answer.
Check our our list of things we checked along with our reasons for checking, and if you have an answer, throw it in the comments!
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[@eddiereichel9354]

As an auto shop owner one of the hardest things to explain to a customer is that "new" and "good" have 2 different definitions

[@SweatyFatGuy]

Yep, a few too many times over the last ten years I have gotten parts home, installed them, and they didn't work. Alternators have been the big one lately, so I rebuild them myself. For the last 30 years, starters have been an issue, so I get the gear reduction units to spin my big inch Pontiacs.

[@1234Testicle]

NEW never ever worked

[@jerryedwards456]

Bi-metal chinesium

[@fratzogmopars]

@@jerryedwards456yep, I blame Chy-na.

[@1STLAR2147]

Yup! I recently installed four new auto zone master cylinder’s in a 93 Chevy 2500 truck. Couldn’t get fluid at the rear wheels. Got pissed and ordered one from car quest. Fluid in three seconds of bleeding. Quality is just not there anymore!

[@Dick_Gozinya]

Put a new plug in it and see what happens. Sometimes you never end up figuring out the cause of weird problems like this.

[@albertgaspar627]

'hear ya on this one. Put an aluminum radiator in my Olds 442 a few years back, drove an hour in July heat to a car show, 180 degrees all the way on back roads. sat all day at the show, drove home an hour on the highway, went back out 15 minutes later...coolant all over the driveway, radiator blown open. hmm, ok, put a copper one in, went to another car show, sat all day no prob, got home, went outside to get the mail a few minutes after shutting the car off to go inside...another big puddle. this time it blew the lower radiator hose off. now, i'm glad she got me home both times, but...wtf? had the rad cap tested, came back "ok". tried everything else, finally bought a $200 test kit, and found my rad cap was "ok" alright...it stayed open to 25+ lbs of pressure (as high as the kit would test). so i guess that's how she ran 180 degrees and blew once i shut off the engine and clutch fan...but why not blow at a show instead of in my driveway? (again, not complaining...but i don't believe in magic, either)

[@jamest.5001]

Open the gap, and heat it with a torch! See if it closes again!

[@scootertrash7944]

It was hard to tell in the video , but it might be the center electrode got loose at operating temp, and moved up and down but at room temperature it is tight? comparing the length of the center electrode and the angle of the ground strap should be pretty easy, or heat it up and try to move the center electrode. I hope someone figures it out. It will be interesting to know

[@mlstrawxj]

We had a plug in my sons car that had a loose center electrode. It would move relative to the ground strap. Took us way too long to find that problem.

[@DanEBoyd]

I once had an '89 Ford Tempo, and when I pulled the plugs, I discovered that some of them were branded Precision Tune! On one of them I pulled on the terminal lug where the wire clips on - and the whole electrode came out with it!! It's been over ten years, so I don't remember, but it might've come out when I pulled the wire off.

[@NBSV1]

Would make me wonder if it’d be tight when cold, but get loose once it gets hot.

[@davidleonard8369]

I went crazy trying to find an intermittent dead cylinder on my friend’s dune buggy. Laughed my ass off when I turned one plug over in my hand and the center electrode slid down and closed up the gap.😮

[@uglysteve1]

Unc, what are the chances of a piece of carbon coming off the exhaust valve and doing that when the piston comes up? If so there ma be a small mark on the top of the piston. A lot of things would have to line up for that .

[@crautoguy8384]

Champion plugs are notorious for that

[@allhailinternalcombustion]

It was fear. That ground strap wasn't about to get hit by that piston, so it moved.

[@jangell1320]

I’ll go with your answer. Makes perfect sense!

[@kimjameson7979]

Somehow, in the cartoon part of my twisted mind, that makes perfect sense. That scaredy-cat plug may well have screamed like a little girl, too, just before detonation and being deafened and blinded by the light. Serves it right.

[@MrTheHillfolk]

​@@kimjameson7979 Blinded by the light? Little Early-Pearly came by in his curly-wurly and asked me if I needed a ride. (Lol went to school with someone with your same name but I graduated in 91)

[@0004612]

@@MrTheHillfolkyeh! One of my favorite tunes.

[@reaper20015]

🤣

[@johnfrinkjr3865]

If the ground strap didn't move down, maybe the electrode moved up somehow. Closing the gap.

[@CharlesVanNoland]

It really looks like the strap is bent down to the 'trode IMO.

[@madmax2069]

​@@CharlesVanNolandyeah I was noticing that

[@craighansen7594]

Had the resistance element In resistance plug start to burn. It moved the center electrode out, basically into the gap closing it.

[@dlyrag755]

If you have no answers to this, nothing left to do but try repeating the process and see if it happens again, then go from there. Very strange for sure.

[@machwind3266]

Yes, true. Put a new plug in and repeat the conditions.

[@sometimesleela5947]

@mach Perhaps put that plug in a nearby cyl as well. See if the problem follows the plug or the cylinder.

[@JohnThomas-vb9se]

There’s been a lot of other people having plug problems. Mostly with the porcelain blowing out of the center. Maybe it’s settled. Check the height from plug to plug.

[@MrNota500]

That was my thought. Is the porcelain broke giving it the illusion that the strap moved? I think Tony would have caught that though.

[@22099dscott]

This would be my guess as well. Every new part comes with a warranty for a good reason. Many years ago I ran into a single new plug out of a box of 8 that came with the porcelain just loose enough to move. Set them all to 35 thou. Started engine and it had a miss on idle. Connected the oscilloscope to the engine and found one cylinder with a very short height firing voltage. Checked cylinder power output and that cylinder showed the least power drop. Shut off the engine and verified that 5 and 7 wires were not crossed before pulling number 5 plug. Gap looked good so I swapped plugs from 5 and 7 and ran it again. Now it was cylinder 7 showing the low firing voltage. This time instead of having scope do the cylinder power test I tried pulling the wire off the plug. As I twisted the boot it felt funny and before the boot came off I happened to notice the firing voltage jump up to match the others. Pushing it back on dropped the voltage. Took the plug out and stuck it in a vice to hold it and then pushed and pulled on the wire connector. You could see the gap change from a normal appearing to damn near 0. Changed all 8 plugs (just to avoid future warranty comebacks) and problem went away. Champion didn't even question the warranty claim..

[@ericdeven1296]

When its hot it might loosen up?

[@jeffgriffith7003]

I’ve personally experienced this exact issue

[@aussiebloke609]

@@MrNota500 The ground strap _looks_ like it is bent at at acute angle, rather than the close to 90 degrees you'd expect. But that's just from what I can see in the vid, so no guarantees.

[@SweatyFatGuy]

Its obvious what happened when a plug gap closes. The gnomes inside the engine get irritable, want to turn off the light, so they whack the ground strap with one of their hammers they carry on their tool belts. The solution is to use vodka as fuel, because the gnomes and the engine fairies love that stuff. Also they get too drunk to even find their toolbelts, let alone discover then touch the ground strap. You have no choice but to keep the piston gnomes and engine fairies happy.

[@BigBeavrSlayer]

This is ridiculously funny, only cause I know what you run for fuel 😂

[@samhicks97]

Speaking of gnomes, reminds me of the stories from miners in the 1950's of the allusive and mythic Tommy knockers.

[@SweatyFatGuy]

@@BigBeavrSlayer I like to keep the gnomes happy, the fairies like nitrous. Stick twisted little bastiges that they are...

[@MrTheHillfolk]

Those little fellas get around. Ever work on a late 80s Honda car with carbs ? They can fit like 300 of those little gnomes in those vacuum hose boxes with their adjusting screwdrivers and wrenches to keep the mixture right as you go down the road.

[@MrTheHillfolk]

​@@samhicks97 The Steven king book was freaking awesome, as usual the movie sucked if you already read the book. Same as Christine

[@brandonlink6568]

Next step should be to switch #1 & #2 plugs and run it and see if it's a problem with the plug or the cylinder and go from there

[@wendyvic4046]

My first thought.

[@UnfinishedProjectDartSport]

Improper metallurgy on the strap and caused it to bend similar to how a “breaker” works?

[@damarapoledna3636]

Lol

[@cannednolan8194]

Possible heated and bent with heat.

[@mvg-1776]

That's what I was thinking. Garbage materials.

[@thomascroft2376]

This was also my thoughts. Metallurgic failure in that one plug. Once he worked the engine it got hot enough to move the strap.

[@jerryzotta4482]

That is the only possible answer I could think of too.

[@keithroute8906]

Good mystery, since I am older than you I will tell you one thing from experience you may have seen or maybe not. If you have mice anywhere around, they drag acorns or drop hard nut shell pieces in the inductions of motors. Sometimes a piece of shell gets pasted inside a runner and falls off later, can even be months later, washed off by fuel and air. Happens most when you run it hard in a hit down the track or like in a burn out. The piston will smack a piece of shell into the spark plug and there you go. I have had it happen to me. I run a mouse free shop now but in the past mice ruined interiors and motors at various times. My old shops had cracks and crevices from age and they always got in. If you leave a car outside overnight one or more climb up and in. So keeping the shop tight, the old cars inside helps keep mice out of the shop along with five gallon bucket water traps, poison boxes and the shop cat if one gets in.

[@jetmec]

Hi Tony it sounds like the centre electrode has dropped, this may be due to a badly made plug

[@shrek_428]

I'd try putting a thicker washer on the plug and send it, it might be that the piston is just barely touching the plug. If it hits even with the thicker washer, then off comes the head.

[@wendyvic4046]

Was second thing I thought; the plug seat on that chamber may be machined deeper than the rest.

[@truthboomertruthbomber5125]

Last year I had a plug fail on a twin cyl riding mower. The motor was running perfectly and out of nowhere it started skipping and also sounded weird. The ceramic portion had come loose in the outer body. Compression was leaking causing the miss. The ceramic was really loose so it was obvious.

[@natevanlandingham1945]

I had one do that on a chainsaw. Took me awhile to find it. I thought it was a carb issue. Rebuilt it and went through it a few times. Sometimes it would run fine other like it was leaning out and others it wouldn't even fire. I pulled the wire off the plug and saw it was moving all around. I don't believe this to be his problem because he is holding it and would see the ceramic loose.

[@leahcimthgirw3163]

Uncle Tony the core broke inside the insulator causing the misfire

[@billwilliams2767]

I think it probably happened when you were attempting to put the plug in the hole. Unless you put them in using your fingers. I usually have mine in a socket with an extension. You probably just bumped it going in.

[@DanEBoyd]

That's why you lower the socket and plug SLOWLY, if you're going to/have to do it that way.

[@Tumbleweed_Tx]

and it didn't make itself apparent until after a couple of runs because that's how long it took the plug to foul up.

[@leinie6683]

Im trusting that Uncle Tony didnt do that- If it was mine - yeah maybe but not on his

[@whatyoumakeofit6635]

Definitely a good possibility. If it were me I'd think I would have remembered bumping it on the way in. Also, if I bumped it on the way in, I'd pull it back up and double check it. Still......I'd know there is always a possibility, always. Best thing to do at this point is replace it, being extra carefull on the install. Then keep a eye on it.

[@kevinmccarthy3379]

Makes sense to me

[@Jeffer54Jeff]

I've seen this before, and it turned out to be over revving the engine.

[@nerizascholl6912]

I agree totally. To much Timing, To much spark plug gap, Bad Fuel, Over Reving is exactly how to Destroy an engine! My Dad did the same thing with his Chrysler 300 440 back in the day and had 3 spark plugs BENT!! Detonation is not your friend. So don't invite it in!

[@jamesmccafferty7045]

My best guess is that you bumped the spark plug when you installed it last. It ran on .006 gap till it finally fouled out after a couple runs.

[@72442conv]

This is 100% what happened. This has happened to me before, where I have bumped the ground electrode while installing it.

[@jeffreyvietzke228]

As a retired auto tech with over 40 years in the industry, this was my take as well. It's the only plausible answer.

[@Sjutern]

Agree, have happened to me..

[@throttlebottle5906]

unless it was dropped are you banging them into the hole with an big hammer? lol

[@Euroburger]

Are you sure the ground strap was bend up? Could it be the center electrode that moved down?

[@user-ld9ke2yv6t]

I vote for the guts moving in relation to the ground strap. The electrode cracked inside causing the misfire leading to the carbon buildup. Egg before the chicken!

[@anthonymichael5154]

Had the same problem with some AC Delcos on my Vette. Bought new plugs and the problem went away. Bad batch is what I concluded.

[@lonewolf744]

Bottle Rocket got pissed off because you're drive Slag and not her. In the middle of the night while no one was in the shop, She took out 1 spark plug from Slag, cussing her the whole time,, precisely bent it and put it back in the cylinder. Case Closed !!!

[@2HacksGarage]

Run a compression test on all the cylinders, see if that one is low. If not, throw in a new plug and send it

[@livewire2759]

That still doesn't answer the million dollar question though... My money is on a loose center electrode, as several other people have pointed out already.

[@rpmunlimited397]

If you are running unfiltered velocity stacks your back tires could have launched a piece of rubber, stone, wood chip or a piece of a pair of sunglasses sky ward on the way from the trailer to the starting line and it came down into one of those funnels on top of the engine. I mean the back tires are kind of hanging out in the breeze.

[@rustyh8806]

I started running an air cleaner after pick up something on the return road. Marked up 2 pistons on opposite banks and bent an exhaust valve.

[@davidleonard8369]

Nonsense! That could only happen to me!

[@aussiebloke609]

Ah, but those funnels are hidden under the grump lump. It would take quite the trick shot to get anything significant in there, remembering it also has to make it past the throttle plates and the valves without getting hung up, so it would have to be fairly small...and then to leave no sign of its passing like imprinting on the piston top, or catching on a seat and causing a burnt valve. Ground strap on the sparkie doesn't show a sign of impact with anything internal.

[@billfioretti3013]

Tony, don't sweat it. Quench to close for comfort on that one cylinder may depend on piston configuration and/or uneven deck. Fingers crossed, hope no engine damage occured. Change your plugs. Set the gaps at .030 or what you normally run. Run it. Pull the plugs. If the gaps don't change again, fine. Again, fingers crossed you should be good to go. There are many unexplainable anomalies in life and in pursuit of those lower e.t.'s.

[@ARfourbanger2000]

The carb sucked up a piece of rubber from the burnout pit, smashed it against the spark plug strap, then burned it up and exhausted it

[@irieman442]

Just a casual observance. It seems to me like the shift on the first run was over reved or valve float. The second burnout there is something burning that comes under the car. Right after the tires go to smoke. Look at the race video again.

[@9vdc500ma]

Detention can do that

[@kragalex]

The ground strap contacted the piston top which is flat. Just enough to bend it. And since you ran it again the mark was covered up. Could be a failing rod bearing, that is not showing anything until the rpm's are up.

[@22099dscott]

It's a wedge engine, the plug is closer to laying on its side in relation to the flat top piston.

[@stevenwheatley4347]

Debris, acorn, piece of stick. This one might be the squirrels

[@AlejandroRamirez-vl8mr]

7 years ago a customer car came to the shop with a miss a day after I did a full tune up on it After searching for the obvious issues with wires and so on I pull the plugs 3 cylinder engine with cylinder 2 plug with a closed up gap and an obvious weak spark, no witness marks, no detonation signs, nothing I replaced the 3 plug set with a new one I had and sent the customer on his merry way Couldn't sleep for about three days thinking about the plug and rationalizing that maybe I hit the ground strap while I was installing it (which I know I didn't do) So fourth day comes, grab the plug and install it perfectly gapped in the number 1 cylinder of my own car. End of the day, 16 mile drive back home and the car develops a miss. Same 3 cylinder engine, same model (Geo Metro/Suzuki Swift) and a miss! and on a 3 cylinder engine it's enough to leave you stranded with little to no power. Surprise surprise it was the number 1 cylinder. that had a miss So luckily I have tools to pull it out and again surprise! gap is closed. Now I know for dead sure that my engine has a perfect air fuel ratio, perfect timing, good quality gas and so on. Gap the plug by eye and get home. Next day same 16 mile drive and I am stranded midway, same issue. Pull out the plug and the gap was closed and now I notice that for some reason, the ground strap feels a bit softer than usual, and the day before I didn't fully notice it but I did feel weird about it. Barely arrived to the shop while limping and missing for about half a mile. Pull out the plug and the gap was closed again!. So i threw out the plug and replaced it with the NGK one I had before. Turns out the plug had some bizarre defect that I've never seen again. 1 out of the set of 3 the customer brought!

[@eddiereichel9354]

Those looked like Autolite spark plugs. They are terrible. I have one sitting on my desk it was for a 5.4 ford out of customers truck. It had less than 50 miles on it and the ground strap completely fell off it. This is just one example. I have fixed at least 10 vehicles by replacing cheapo autolites. If customer cant afford OEM plugs I get NGK for em.

[@mikebrunello243]

Yeah I have had a lot of problems with autolite plugs too lately quality has gotten really bad on all parts

[@malibuclassic77]

I use cheapest level of NGK platinums in all my cars now, foreign and domestic, I never have issues anymore.

[@bobbybrown931]

Lost 2 300 6cyl to the automated power tip. The recommended heat range was way hot causing a spark knock that took me to long to find after distributor , egr valves burnt pistons in both .

[@jonathanabeld2326]

I've started using ngk plugs in everything my 69 f100 with a 400 in it has v powers, my trailblazer with the 4200 has iridiums and my 16 chevy silverado is gonna get the ngk iridium or whatever it calls for

[@robertrio1164]

Autolites are Tony's goto plug brand though he admits the quality is not what it once was. Funny though my buddy had same issue a week prior with new NGK plugs he put in his 4.8 LS. He asked me what I thought could cause it. After looking at the pics said he must have dropped or bumped it prior to being put in. Has stock heads and lower end.

[@jascan1489]

I'm voting you have a rod bearing issue on that cylinder, allowing the piston to hit the plug.

[@briansignorelli7090]

If the bearing is bad enough make the Piston hit the plug u would hear it

[@mitchcrawford7414]

​@@briansignorelli7090not if it has clearance now the electrode has moved enough

[@indianaslim4971]

Would have left a witness mark

[@jascan1489]

With those I'm sure loud ass pipes, maybe he hasn't heard it yet. It's the only thing that makes sense, especially with only that 1 cylinder partially closing off the gap. That's also if 100% sure the plug was gapped correct and not accidentally bumped before install.

[@jascan1489]

@@indianaslim4971 once the piston " possibly" kissed the electrode, just enough to close the gap, and ran after the fact. There wouldn't be any visible piston marks.

[@ttiwkram]

I agree with the "loose center electrode" guess. Leave the plug in an oven for an hour at 400F, then pull it out and see if you can move the electrode 0.029".

[@andme9408]

I used to heat treat metal parts for a company. We would put 100s of small parts in each basket. We would grab a handful of them after the process, and Rockwell test them. Most of the parts would be with the range. I would just for kicks test double the amount I was supposed to. Bam I would get some soft and some really hard. The process for mass production is not precision. On aircraft parts they all had to be exact, but mass produced stuff we did the hardness had a huge range.

[@lbbruins7958]

Hey Tony! I recall in the track video that Art said he noticed some white smoke at some point in your launch. Perhaps a small leak in the head gasket? Since water doesn't compress...may not have been enough to break anything but enough to take out an electrode? Good tech problem. Can't wait to find out what you've found.

[@Desertwolf426]

Although it looks like the ground strap has bent to the center... i suppose something soft could do that... piece of silicone/rtv from the tunnel ram possibly? Ive also seen improperly bonded or cracked center electrodes shift and fall out towards the ground. This would also explain the misfiring... my bet is just something soft being digested though.

[@outlawbillionairez9780]

Mistery solved! Andy . Unity Motorsports Garage. Sabotage.😮

[@EarlwithanE]

I continue to enjoy your videos UT. Mysteries and all. Thanks for taking us along for the ride(s). 👍💪

[@gregmacdonald6773]

What about a defective plug? Is it possible the electrode itself dropped or was sucked down inside the ceramic ?

[@jhonditch4269]

that is my thought

[@harrismaynord871]

same here. measure distance that electrode extends past ceramic. compare to other plugs.

[@michaelmurphy6869]

Could have been a allot of things that may caused that situation. You could have sucked in a bug. Just a guess. Possibly a piece of rubber thrown up by one of the front tires during the beginning of your second run before the engine reached its max rpm. During the ingestion it bounced around in the cylinder contacting the plug ground electrode thus closing down the gap but not completely closing it. It being fairly soft it shouldn't do any damage to the plug, valves, piston, cylinder and head. By the time you reached your shifting rpm it had burned away (at least what was left of it and causing the misfire heard and felt) and was pushed out the exhaust, not leaving any witness/impact marks (if there were any marks they would be covered up by the carbon fouling)while you still had half a track to run. Causing the plug not fire properly and the carbon fouling to occur. All that can just happen in a fraction of a second. Again just a guess.

[@jimlahti1613]

Agree, chunk of rubber, cigarette butt etc. No inner fenders, don't recall seeing screens on the velocity stacks. Lots of air gets under the front of that thing. On the 1st run in the previous video there is a piece of debris in the center of the lane in front of the car that gets picked up as the car goes over it. Down track he gets out of the groove & moves toward the center line, may have picked up something there.

[@audikid89]

Water in the combustion chamber! Not enough to Hydro lock but enough to bend the spark plug ground strap on the compression stroke

[@arthurxxxxxxx6664]

The answer is simple. Don't drink alcohol when you are working on an engine.

[@justinschmidt9180]

Between the 1st and second run you did put some timing in it . Maybe it was just enough detonation to bend it but not put the heat mark on the ground strap. Or a rod bolt streched slightly

[@The_R-n-I_Guy]

I was thinking detonation pressure. The ground strap is the weakest part in the combustion chamber.

[@brucef5892]

When he was cranking it with a ground problem i wonder if it didnt snort back off camera and bend it

[@todddenio3200]

Try another plug in that hole and put that plug in where the other plug was and give it another test. If it happens again to that same plug, then you know it is a faulty plug due to poor metallurgy. If it happens to the other plug or any of the other plugs, then there is an issue to be found. If it doesn't happen again then it's just a fluke incident

[@charleselertii6187]

I like this. Clean and regap all the same plugs, swap positions with the bad plug, give it a a couple of burn-out runs. See if that bad plug goes goofy again or if there is something weird about that cylinder.

[@DanEBoyd]

James Kilpatrick wrote that a fluke can only be a good thing. If a bad thing like a bent ground electrode happens, then it's not a fluke - except maybe for the car in the other lane, which pulls ahead as a result of that bent electrode.

[@jeffreyvietzke228]

Tuned cars in the industry from '79 t0 '21....42 years. Thousands of cars. Huge UTG fan and also loved your Cars Illustrated articles from 40 years ago. That plug did NOT get close-gapped after installation in the engine. It got close-gapped DURING the install, by dropping (which you did not do to your recollection) or by hitting the edge of the cylinder head while inserting (BTDT but usually it just gunks up the plug). For whatever reason, the gap was .006 from the jump, and it ran ok for a short time because it was NOT YET CARBON FOULED. You yourself have a world of experience and ruled out virtually every other scenario. It got close-gapped outside the engine, IMO. Your content is excellent, BTW.

[@NathansMoparGarage]

I had a problem with Champions magically opening up the gap. It took a while to figure why it wasn't running right. Last time I used those.

[@pauljones2031]

I second autolite plugs being crap. I used to use them in my small engine repair shop and had lots of bad ones, even 25 years ago it was like this.

[@todddenio3200]

They are still better than Chumpion.

[@malibuclassic77]

@@todddenio3200 seriously Champions are absolutely horrible, they last about as long as an oil change.

[@DanEBoyd]

As a Ford guy, I've always gone with the Motorcrafts instead.

[@billfioretti3013]

Autolites were the go to plugs before Bendix bought the division from Ford years ago. I'm a Ford guy but even my Mopar buddies used them successfully. back in the 60's and 70's. Don't know about the current ones. I have boxes of the older Autolites and 70's Motorcrafts I use in my classic cars and racecars.

[@pauljones2031]

I don't know what I'd use in a track car, but for daily drivers I use ngk.@@billfioretti3013

[@chaseman113]

Probably not your issue, but I bought a truck so packed with carbon it had gained a knock. 71 F250 390. Only I didn’t know it, I only thought I had a noisy motor. But I’m a fan of running ATF, seafoam or even spray water down the carb to remove built up carbon. I generally do it a couple times for a new to me vehicle until the resulting smoke lessens. And admittedly, I think it’s the funniest thing to go down the road & roll white smoke like a steam engine. Lost story short, the motor got quieter. Knocks just disappeared. So I can only assume, the motor had built enough carbon up to make a “knock” and my multiple cleaning attempts got rid of enough carbon to do something. The plugs came out gapped a little tight, but I didn’t have any missing either. 🤷🏼‍♂️

[@mattrafalko2105]

Going back and watching the other video at the track, looked like blue smoke coming from the passenger side. I’m not sure if it was just my eyes but that’s #2 side . Keep up the strong work uncle Tony

[@jseal21]

Or the detonation closed it from cylinder pressure right off the bat and deep heating never happened because it closed and turned off the spark immediately...

[@danw.3291]

Interesting especially without any marks to the piston or ground strap... you definitely don't seem like the type that went to jam it in and bumped it on the way in but it's possible as you were installing it the phone rang causing you to jump a little.. hitting your knee all while at that exact same moment causing your arm to jump bumping the ground strap into something....

[@jseal21]

Minor detonation was gonna be my guess. Is it possible the fouling is covering up the blueing? Another option is a metallurgical deficiency ???, might be just soft enough to not handle the cylinder pressure under heat but not as likely as detonation because it would have already presented itself earlier...

[@throttledavidson1241]

I saw an episode with Steve Morris where the insulator had been compromised and was leaking around the plugs electrode.Just my 2 cents.

[@rollandsicard1628]

Tony: Eliminate weird ground issues. Connect another heavy cable from battery negative back to one bolt of the starter. Then another heavy wire from Starter mount bolt to ignition coil case or negative side. Eliminate funky ground paths. Use same size cable or larger as used for battery positive. Go get some welding cable and lugs and eliminate all questionable connections go battery and engine.

[@BigHossZO6]

Tony are you certain the center electrode didn't slip down .029 or so inside the insulator? It's not one solid piece of steel from one end to the other. I've seen this before when you pull the plugs out and the center electrode is just floating loose in there.

[@karlbishop7481]

But it looks to me that the ground strap is bent down towards the electrode but it is hard to see with all the carbon. The electrode moving is the best explanation so far.moving

[@67L-88]

Two things come to mind, a bad rod bearing or a bad plug

[@Hogiewan1]

Man, the rod bearing was my first guess too!

[@daledavies2334]

Two things; A bad rod bearing enough to smack the plug would produce a huge knock, knock let me out sound. If the ground got tapped it would not be 90° to the electrode. Poor QC/QA with a bad plug, possible.

[@jasoncardoza6375]

You can definitely hear a knocking in it while it’s running. How come nobody else hears it?

[@johnpublic6582]

@@jasoncardoza6375 I thought I heard it at one point when it was at idle. I figured it must be an exhaust leak since no one else seemed to hear it. A new pllug and a few seconds of RPM would figure that out.

[@jasoncardoza6375]

@@johnpublic6582 exhaust leaks tend to have a ticking sound on camera audio and by ear. Go to the track video and you can really hear it right off the trailer after he stayed at roughly 1500 rpm and let off. I’m not trying to sound like a dick. It’s losing power probably because it’s eating itself alive. 383s are awesome motors but it’s not gonna be good if it throws a rod. At the very least he needs to cut the oil filter and inspect it. EXTREMELY cheap insurance

[@jhonditch4269]

biggest mystery I gave my father with a slant six how did I drive it until no point material left on points before I complained 'something doesn't seem right' but that was in the 60's and things are new and improved now, btw dad only used champion plugs and we would clean and re-gap to save pennies, which had 100 times the value then.

[@hunnybunnysheavymetalmusic6542]

3:00 After 10 seconds of reading various posts, I can not rule out a dislodged park plug electrode core too, but I would still check the piston head for dings.

[@jamesmarze9850]

Tony random question, why don't you have air cleaners on your hot rods? That's my guess

[@TheJohnbjunior]

Or screens, something, debris is everywhere!

[@DiamondTTrucks]

With all due respect, the forensics you completed leave only the most likely scenario, you did it.

[@mdcuddy3286]

Tony, when we ran our cars we always had a set of warm-up plugs and a set of running plugs (hot and cold ranges). We also always indexed the plugs for each cylinder. Had one event where a flooded cylinder closed the gap on the compression stroke right after startup.

[@edc6333]

Gremlins Uncle Tony, they are always screwing with my stuff the mischievous little buggers.

[@timjefferson2137]

The only thing I can think of is that the piston might have touched the plug. Does it need to be indexed? IDK what your clearances are.

[@sodiorne2]

That was my thought. IF the plug was indexed straight at the bottom, it is really close to the top of the piston. I don't know what pistons he used, but if they are dome pistons that would be my guess.

[@Cstoreri]

Brian Cabral ?

[@WhitentonMike]

We can appproach this from a likelihood perspective. We have an extremely experienced person that has developed habits to prevent the most common causes of a damaged sparkplug. It could be detonation but none of the other cyls show any signs of that. Debris of some sort is the next possibility. If the debris were a hard material there should be signs of impact and there should be signs of where the hard material came from. Also, if it were a hard material the size would have to be 29 thousands to not cause visible damage. A washer maybe? Next debris possibility would be a softer material that would deform or break apart on impact. The first two things that come to mind are gasket or rtv. Examine the carb baseplate gasket for missing chunks from the inner edge. Also the intake gasket may have a piece missing. Lastly, examine the inside of the air filter for signs of damage like a piece of rubber or something with a chip missing. Without knowing the specifics I would seriously examine the filter.

[@garyweber7139]

Back in the Seventies we would have some fun with our buddies hot rods, sometimes we'd pack newspapers up the exhaust or other stuff, sometimes swap plug wires, or regap their plugs, wrap tape around the air cleaner, disconnect the throttles, and yes we'd each get the treatment in return. I got all of my gas siphoned out once, after freaking out, it was returned. Debri in and engine is no joke, I lost a small screw clamp for a fuel line down into the intake (somehow?) in a fresh engine after a rebuild. I spent awhile looking for it, and couldn't find it. I drove it for two weeks, on the freeway and around town traffic no problem. Then one morning I start up and bang, bang, bang, No.5 piston and cylinder chewed up. So resleeved and gone over again the engine was saved. Crazy stuff happens this was the second worse mistake on an engine I've ever done, so far.

[@ACV975]

I would say that you ingested a small stone down the carburetor, and when it hit the spark plug, it just shattered to powder and was exhausted.

[@karlbishop7481]

This is one of the most plausible ideas so far? Probably not a pebble, stone or whatever but a piece of debris from the hood or from the engine bay somewhere.

[@ACV975]

Yes even a piece of hard rubber or even plastic could do it

[@marccres6619]

Porcilin slipped, had one blow out on a stock motor ,why not suck in on a intake stock hot and it is poor fitting

[@Sam-zp5rd]

I had a similar experience many years ago with a Thunderbird turbo coupe 2.3. I was playing with the boost levels and I had the boost cranked up over 20 psi, and it started missing really bad. When I pulled the plugs, one of the plugs was all black and the electrode had closed the gap like yours. There were some signs of discolouration like they had seen some heat. I put new plugs in and dialled back the boost, and never had that problem again. at the time I had figured that it just ran really lean with the boost levels and melted the electrode down, but I never really had any proof That that’s what happened.

[@albertgaspar627]

all i can say is i love turbocoupes, had an 86 with the SVO intercooler in the grill. best alternative to a Foxbody (when you're too young to afford the insurance), had to sell right before gas hit $5 a gallon at the pump. best $1,000 car i ever bought, closest i'll get to a Gates Lear 25 corporate jet since she was fully optioned out and loved interstate travel :)

[@MrGGPRI]

Here's one; my hypo 327 SBC in my Deuce became hard to start, it ALWAYS cranked good and when it did start, it would spit and spudder.. so I checked the tri-power carbs, StreetFire CDI and distributor and wires, plugs, compression, fuel lines and tank-no help. After a few months grinding my teeth and wasting hours of time on the carbs, I took a GOOD look at the CDI and while checking voltage to it found a good 12.6v but when cranking, it would drop to mid 9v ?? Since I did all the electrical, I went all thru the system but found no reason for the huge voltage loss so when back to the side mount Delco battery in the trunk (12.6v) and it measured a 10.6v when cranking !! So the obvious was the battery under load had a collapsing cell (2.0v) and coupled with another drop due to starter draw (1v) created a 3v loss and the CDI REQUIRED 9.8v to fire the plugs !! A fresh battery and we were back rockin’ and rollin’… Senior wrencher-- since 1958.

[@HFG]

If it were me, I'd think that I accidentally bumped the plug when I was reinstalling it.

[@WhiteTrashMotorsports]

I had a nissan z24 engine that would close the gap every once in a while, I always wrote it off as a random detonation/ pressure spike.

[@nicholasagnew2792]

Strange, cuz those are hemis and shouldn't detonate.

[@WhiteTrashMotorsports]

@nicholasagnew2792 mayde so but it would always smash the exhaust side plug.

[@jackieteegarden795]

What is one common issue with the ground wire coming loose on the bumper at the same time you have the issue with the spark plug??

[@jameshall6294]

Not a mechanic, so take this idea with a heapin' bucket of salt, but maybe during the starter fiasco, cylinder #2 got slightly flooded with gas, and when the engine got turned over next, there was enough gas in the combustion chamber to push on the strap and bend it out of spec? Again, I'm not a mechanic, but without there being any other debris, or any mark on the top of the piston to make you think it spun a bearing (I have *zero* clue as to how much gap there is between the top of the strap and the top of the piston, so just spitballing here), compressing some excess gas is the only thing that makes sense to me.

[@funone8716]

I believe you. You really are not a mechanic.

[@jmwingert]

Dropped it on the ground, picked it back up, gapped it with the ol eyeball-gauge, cleaned it off with the ol mouth compressed air, threw it back in the motor. All this while in mid conversation and thinking about something else. Instantly erased from long term memory. It's my theory

[@chuckyz2]

No Air cleaners? Chunk of rubber during the burnout found it's way into #2. Got between the piston and plug during the compression stroke. Then was sent out the exhaust on fire if not incinerated, never to be seen again. That's my final answer.

[@franktaylor7617]

Maybe something from one of the carbs fell off?? If it was brass. It may not leave a witness mark or any other damage. Id start looking at the carbs for missing bits or bit. Maybe a butterfly screw? Keep us posted and what do we win if we're right??? T shirt I say would be a good idea.🤨 Cheers from the PNW Seattle WA area.

[@briansignorelli7090]

Yeah that sounds like the best idea yet

[@franktaylor7617]

@@briansignorelli7090 Winner winner chicken dinner???🤷

[@bobbyoshomebuilt2544]

You answered all the usual questions, I'm stumped. Compression test for sure, low, disassemble, normal, new plug and test. If I didn't know the mechanic I'd blame him. As always, thanks for the content.

[@blau325]

Strap was weak and bent when it got up to operation temperature. That is the most logical reasoning.

[@markdavis3362]

My best guess would be, one of those propellers off of a maple tree got sucked in on a high rev when the strap was hot and a little soft.

[@mattneaderhiser4658]

I remember reading, like 20 years ago that John Coletti and Ford built an sn95 Mustang with a built Boss 429 motor in it. On one of the first passes they said they over revved it and somehow pinched the gaps on the rear plug on each bank shut. Take that for what it’s worth.

[@glennnickerson8438]

It happens to the best of us--including UT!😎

[@dirkbonesteel]

Sherlock said After all possibilities are eliminated what ever is left is the answer. So maybe distraction while installing the plug and it was just noticed.

[@Imnotyourdoormat]

HP Books had an illustration of how High RPM High Compression Big Block Chevys routinely close up plug gaps, but that's across the whole engine not just in 1 cylinder. Better dissect the oil filter 1st. Then since it's external maybe the oil pump. Then pull the pan to check that connecting rod. Could be a piece of carbon or broken ring but not on a new engine. While I don't suspect this at all here, especially after being scoped. A crooked speed shop owner back home had this exact same problem on his 427 FORD. He tore the engine down and found a compression fitting ferrule embedded in the top of a piston someone had "dropped" down his venturis for a lil payback for his crookedness. At least that was his problem. With no marks anywhere could it have been a big chunk of new gasket that closed the gap before it got spit out?

[@edenhopkins9137]

Quite a mystery, which I hope will be solved . Great suggestions and possible causes put forward in the comments. Tony , being that during the construction and transformation of this vehicle. . . and arriving at what You call a Street Freak . I think it's true to it's style of car , not only in looks but behaviour especially when it's been to the strip . Keep on it ! The Slag Hammer will have its day !

[@markduvall5918]

I have a 74 350 2 barrel Rochester with an 86 factory HEI distributor with AC Delco 2 plugs. I set the gap at 50 and it runs perfect.

[@drifterengines243]

The nut behind the wheel is reving the engine to hi during the burnouts

[@AvidV8Fan]

Look at the centre electrode. Has it somehow moved down towards the ground strap.

[@jimkalfakis9893]

Tone make sure the inner porcelain electrode piece didn’t loosen or break, and came out a little.

[@glennnickerson8438]

I kinda agree with some of the comments I've read. A piece of debris entered the cylinder, struck the ground strap and ejected out the exhaust. It's the perfect crime, no evidence, no witnesses!😆

[@kentkirkpatrick7953]

Hmmm... Pulled in a piece of rubber from said burn out? Its soft yet hard enough to bend with no damage I'd suspect. Them big o'l funnels on top sure help swallow thing's I bet!

[@kawaiirunnersdriftclub]

That happened with my friend's VW Fox, 4cyl 1.6L stock engine, running alcohol (Brazilian car, some did came stock with 11.5 or more compression to use alcohol). We never bothered to check what was the cause, I just put the plug back on the OEM gap and back into the head, Never had any issue to this day but now you got me curious!!!

[@grizzly766]

Squirrels crawled up in there with a tiny pry bar to mess with you.

[@MartinRanger65]

What’s the measurement on the electrode from the base of the plug? Retired electrician, hobby mechanic. Love the way you explain things.👨🏻‍🦳👍🏼

[@highdesertworkshop]

As you know the heat signature where the ground strap bends is your timing indicator, check your cap and wire to that cylander.

[@michaeledge8905]

Budget spark plugs made from soft materials. Bosch comes to mind. Had a few of the breaking in two coming out.

[@joshandnissa]

The only time I ever had this happen it was detonation and there were no other signs and no audible pinging.

[@robosting9288]

Had the same issue on a motor, no reason to think piston hit it but, indexed new plugs and no more issues

[@petervokes3774]

I’ve had something similar happen on few random occasions here in the UK. No evidence of mechanical damage or witness marks, and seemingly inexplicable. I used to trailer the car to the track about 30 miles each way. Like you, I have an open carb and an open (no mesh) cowl scoop. Not that it really matters, but the car was an 1977 Triumph TR7 with aluminium 5.0 Rover V8 (UK development of Buick 215) with single Holley double-pumper. A chap at the track, after discussing my gapping woes, pointed out that perhaps I should cover/seal the bell mouth before trailering. After that, I wrapped the intake up with plastic and the mystery gap closure syndrome never reoccurred. He put it down to something like a stray road chipping finding its way into the bell mouth, getting sucked into the engine and trapping between piston crown and plug, thus partially closing the gap. No evidence of witness marks because the debris, not being hard like a ring land, crushes at the point of impact dissipating energy and lowering the force exerted on the plug electrode/piston so as not to totally close the gap or bend the electrode. The dusty remnants of the chipping of course get blown out the exhaust valve leaving little or no evidence other than the reduced spark plug gap. You’d be surprised at how much debris is floating about and getting flung up in traffic. Never a problem on the track to run an open carb as it’s pretty clean air. I would never run a car or bike on the street without filters, but always do on the track. It simply hadn’t occurred to me that, just because the engine isn’t running and the car is sitting motionless on a trailer it isn’t going to get some foreign matter in the intake! I also used to make the school boy error of not checking the bell mouth for debris BEFORE starting the car and rolling it off the trailer (simply because the bonnet was shut and it was too high up/awkward to do on the trailer). I did however always check them when I lifted the hood after getting it off the trailer, which is obviously too late as anything in there would have long disappeared into the motor! Tony, do you/did you check your carb bell mouths before starting Slaghammer and rolling it off the trailer? I can see you don’t seal them up when transporting the car.

[@reason2gether]

Tony, I had the same exact issue with a pair of new SB Chevy Dart Sportsman cylinder heads. In my case, it was an issue of the casting flash in the chamber at the very end of the spark plug hole threads. If indeed this is the case with yours, you will be able to repeat the issue just by screwing another correctly preset (gapped) plug into the hole fully, then removing it and checking the gap again. If the plug has the same ground strap orientation that enters the chamber by the casting flash, it will do it again. A way around this until the head can be removed to grind the flashing away, is to pre-bend the outer edge of the ground strap inward toward the center electrode to allow the plug to clear the slag/flashing as it turns all the way to its seat and is torqued, then gap the plug and install it. If it clears, just make note of it that it must be set this way every time until the head can be removed to grind away the flashing/slag. The fix is as I said, remove the head and grind away the flashing that got by quality control and machining. Let me know if this helps. God Bless.