Big problem..or not ??

[ga.spyder]

Okay,a little background .My 82 Spider has been the model of consistency.6 years of almost trouble free service,80K on the clock.I went into my 'Spring into driving season' program this week.Changed oil,diff dope,tranny fluid,etc...I do this every year ,even though the car probably doesnt go more than a couple thousand a year.Today ,the plugs.I always pull the wires,vacuum any debris out before pulling them to try to remove any debris.1,2,and 3 were uneventful.I put the extension with two swivels on the #4 plug,and it was loose.Barely hand tight.The plug was very dark.This explains why the car seems to miss on startup,low idle until I get up to temp? I can only figure that I didnt get it tight last year
I put in the new plug,and started the car.I had a loud tapping noise,and a miss that definitely wasnt there before the plug change.Loud!! I freaked ,checked wires,AFM hose,plugs anything that I had touched.Nothing.I started it back up and was ready to cry.Then,as it it got to 120 deg.,I revved it to 3000 a couple times and...it was gone. I drove the car for a 1/2 hour,shut it off and restarted several times,let it sit,restart and nothing.Other than a much improved idle and smoooth power,it is fine.
My theory(shared by kmac,who I called earlier) is that either carbon from inconsistent fire in #4 or possibly something getting into a cylinder?Any theories or feed back is appreciated.

[maytag]

I'd suggest two things to check that'll help you determine if you have a problem still....

first, pull the plug again. See if it looks like the electrode has been hit by anything? sometimes, something bangin' around in a cylinder can hit the plug a couple times and it'll be evident.

second: do a leak-down test.

I'd say that it is possible you got something into the cylinder, and it got lucky and exhausted out the valve. But the damage it COULD've caused before that is significant. so just check it out.

Good luck, and keep us posted.

[ORFORD2004]

I drop a bolt by accident in one cylinder a month ago and i bought a snake camera with a hook to remove it.

[kustom]

I had the same problem 3 years ago when I also changed plugs. The knocking sound would come and go for a few days, and eventually disappeared. I spent hours trying to see if something had dropped into a cylinder, but couldn't see anything. I have been driving ever since with no problems, and no more strange sounds. I assume whatever was in there left through the exhaust, or is embedded in the head . Either way, my car has been fine for the last few years and hopefully yours will be too.

[ga.spyder]

Thanks guys,I did pull the plugs an hour ago and they looked fine.It was a loud tapping noise,almost definitely coming from one cylinder.I was so careful to vac around the plugs before removing.Very odd and a little unsettling.The #4 plug had definitely been firing inconsistently for a while.I feel like an idiot for not checking it sooner.I assumed I had a bad AAR.The car is now running and idling much smoother,and the noise has completely disappeared! Is a hunk of carbon coming loose from a cold running cylinder just a myth,or could it really happen??
I had a 76 that I sold to zachmac,that had a loud engine knock develop out of the blue.I had the car towed home,and listed it here,as I didnt have the time or resources to do a rebuild.I started it a few days later,to put it on the trailer,and the knock was gone.This car had set up for a while before I bought it and revived it.Long story short,it is still running fine, years later.SoCalMark suggested that a sheet of carbon had broken loose,after a weekend of hard driving.
I will keep you posted,and keep the opinions/theories coming

[rlux4]

A chunk of carbon sounds perfectly logical. I've seen some pretty heavy carbon deposits back in the day. If I were you I wouldn't worry about it. If it turns out your engine gets destroyed, your car is so pretty it would still be a great object d'art. LOL
Ron

[ga.spyder]

Geee,thanks Ron...I think As you can imagine I was in full panic mode! The car seems to be fine.It is running better than ever.Maybe having the #4 plug firing correctly is a good thing

[RRoller123]

Sticking valve guide maybe could cause the noise? Valve not completely seating, then tap when the excessive gap to the lobe is closed. Carbon deposit could possibly do that too by interfering with seating. Would explain the poor firing on that cylinder too, and also would explain why it eventually goes away. Or goes away when warm?

[majicwrench]

You almost certainly missed something that dropped into the cylinder. And you got lucky and it blew out or got destroyed with all the mashing. It could also have imbedded into the piston far enough that it is not noisy, but odds are it spit it out.
I'm a professional auto mechanic and blow out around the plug with compressed air when doing engines with recesswed plugs. Still just a few weeks ago I changed plugs on a vehicle, and when I started it, ran quiet for 10 sedonds or so then started that dreaded tap. Just like you, I revved it a few times, and thank gosh it went away. No worries, enjoy.
Keith

[124JOE]

one time driving thru milwaukee i seen a semi blowing black smoke for three miles
then some sparks out the exh and a few bigger peices of whatever
then it cleared up.i thought "its going to blow up"but he jusy kept going
i stayed way back

[ga.spyder]

Thanks everybody.The car seems to be fine,cold or warm, the noise has gone away.I think Keith hit it on the head,I must have missed something,and down it went!I will guarantee the next plug change,I will hit it with the blowgun and make sure there is nothing in there!

[steve8462]

i have a slightly unrelated question, but it appears we have some "megaminds" logged in so maybe you can help me. i have a 1979 spider with a carb. the po had installed a Mr. Gasket electric fuel pump in the trunk. i noticed he had the return line disconnected at the tank and plugged. did the 1979 model come with a mechanical fuel pump or an electric fuel pump? what got me thinking about it was the fact that the po wired the headlight switch as an "on/off" switch for the electric fuel pump. also i was looking at a wiring diagram for my car and cant seem to find a wire designated for an electric pump. any suggestions?

[124JOE]

the 79 came with a mecanical pump

[steve8462]

should i stick with the electric pump or go back to the mechanical one?

[124JOE]

i would ditch the ele
because someone scabed it together
and go mec thats what i have
it works fine