Spark plug electrode crushed

[Fishfan]

For background: 1966 Polara 4DR with a 318 Poly which was rebuilt about 7 years ago.

Recently swapped out Holley 2BB (that was flooding) for the (rebuilt) Stromberg 2BB that came with the car. Car was basically undrivable after the swap, stalling on idle in Drive.

On a hunch I decided to change the spark plugs. One of them had the ground electrode crushed into the central electrode. Changed all 8 plugs. Managed to limp the car to carb rebuild guy to see if he could fine tune it for me. He told me two cylinders weren't firing. When he pulled the new plugs, two of them had the crushed electrodes.

What the hell could be happening? The plugs are the right spec for the car. I double checked.

 

[detmatt]

Do the electrodes appear to have suffered serious trauma or just bent so that they made contact with center?

 

[67Monaco]

Plug hitting the piston would be my guess. Perhaps you're installing the wrong ones? Overall length too long? I'd look at getting an Iinspection camera down those cylinders and find out how much porcelain is left in there. maybe someone dropped some carb nuts down the intake...

 

[300cruiser]

I dropped a plug while changing them early this year. Didn't think much about it, just picked it up and installed it. Engine idled poorly and had an obvious miss. Double checked all the wires, still not good. Pulled the plugs one by one and of course the last one I pulled was the one I dropped, the electrode was making contact with the center....another lesson learned the hard way.

 

[Wildaugust]

I'm just wondering, until you changed the plugs, had these plugs been your engine when you were running the Holley? If they were, did the engine seem to be firing on all cylinders then? I guess what I'm thinking is maybe something did get in to some of the cylinders. Could some of the screw heads have broken off the throttle plate screws and fallen in to the engine?

 

[Fishfan]

WildAugust: Before the Holley carb started flooding over and shooting gas out of the vent tube the car seemed to be running fine.

Matt, when I pulled the plugs over the weekend one of them had suffered serious trauma. The electrode was pushed in so far that it actually slid off the side of the center electrode and was pushed so it was next to center electrode rather than on top of it. As I said I replaced them all and today two were bent (including the #2 on the driver's side which was the one I'm referring to from the weekend).

67Monaco, yeah I thought maybe wrong spec on the plugs but then my performance would have been FUBAR before.

Here's a few things to consider:

At some point, I can't remember when, I had had a pretty loud backfire. Maybe that explosion caused the plug to get mangled?

The carb rebuild guy found the distributor to be a mess. The rotor was FUBAR and so was the coil lead wire. We're swapping out the distributor cap and rotor and spark plug wires. Wondering if faults in the distributor could be causing backfires and thus the damage to the plugs?

 

[Polara_500]

Double check your timing - a big, loud backfire could have made the chain jump a tooth or two and if the cam's out of sync with the pistons it will wreak havoc with the plug ends.
Mike

 

[Big_John]

Double check your timing - a big, loud backfire could have made the chain jump a tooth or two and if the cam's out of sync with the pistons it will wreak havoc with the plug ends.
Mike

That might cause the valves to touch the pistons if the chain did jump a couple teeth... It won't make any difference with plug to piston clearance.

I'm really thinking that you have some junk floating around in the cylinders. With the carb flooding out, it makes me wonder if there is some piston top damage and pieces of piston are banging around.

The other possibility that comes to mind is you are using too long a plug. I know you've checked....

 

[Polara_500]

Sheesh, you're right there, John. Seems like my brain is dysfunctional lately. I'm gonna go back in my corner and hide again.

 

[Fishfan]

That might cause the valves to touch the pistons if the chain did jump a couple teeth... It won't make any difference with plug to piston clearance.

I'm really thinking that you have some junk floating around in the cylinders. With the carb flooding out, it makes me wonder if there is some piston top damage and pieces of piston are banging around.

The other possibility that comes to mind is you are using too long a plug. I know you've checked....

If there is junk in there, any way to get it out without removing the heads? A magnet?

 

[1978 NYB]

If there is junk in there, any way to get it out without removing the heads? A magnet?

Yes, if the debris is metal (steel) and not embedded in the piston. You can take a look in the cylinder with a remote camera.

 

[detmatt]

That is what you need to do next.

 

[70bigblockdodge]

Could be carbon build up from excessively rich( flooding volley) but the very small amount of driving after this rich condition it that seems unlikely to be hard enough to bent that much. A compression check is about the only thing besides the camera idea.

 

[Fishfan]

Well, new plugs, distributor rotor, distributor cap and spark plug cables later and everything seems to be running fine. Smoother than I ever remember it. Stromberg carb is working perfectly, cold starts are better than ever.

 

[detmatt]

Great! Still have to wonder though...

 

[Fratzog]

Being technically challenged can somebody explain to me how replacing some tune up parts cures crushed electrodes!?

 

[70bigblockdodge]

I don't know if it fixed it but maybe if there was a piece of debris that now passed out exhaust. Kind of like a kidney stone.

 

[Fishfan]

I'm thinking possibly faulty installation on plugs. Over-tightened? That's what the carb guy seems to think.

 

[Big_John]

Did you check the gap when you installed the plugs? I'm wondering if you banged the new plugs against the manifold or something like that as you put them in. It happens....

 

[1978 NYB]

Was it determined if those damaged plugs were the right or wrong to begin with?