Look what I found

coloradoporsche · 03-20-2005, 08:30 AM

I pulled this out of my new-to-me 79SC.....

It was extremely difficult to remove, and I knew it was stripped as soon as I started backing it out. I was able to put a new one in the hole, and it went in "pretty far" and then got "pretty tight". And the car seems to run fine....for now.

Has anybody else driven around with a sort-of stripped out spark plug for any length of time? I guess I'm about to find out how bullet proof this SC really is.

If I do contact the PO, and he can provide a receipt for a shop that did the last spark plug change, do I have any recourse?

I suppose this is another reason to get the leak down done before buying! The seller seemed so honest.....

pwd72s · 03-20-2005, 08:34 AM

Is it my eyesight, my screen, or are the threads on the plug itself bad???

coloradoporsche · 03-20-2005, 08:39 AM

Well, the stuff at the end of the plug appears to be melted aluminum. It flakes off in silver powder when I scrape on it. And some of the threads on the plug are crooked. So I assumed it was cross-threaded, but I'm not 100% sure what went wrong here. All of the other plugs came right out, clean.

sushinav · sushinav's Garage

I'd recommend chasing/cleaning the threads in the head ASAP. You can do this if you have the correct tap and die set, or make your own by cutting 2 grooves perpendicular to the threads on an old sparkplug, then working it in slowly and backing it out frequently to remove metal bits.

ruf-porsche · ruf-porsche's Garage

Buy yourself a spark plug thread chaser and chase the threads out or bring it to a mechanic. Reinserting a new spark plug into a head with cross threads is just aasking for trouble further down the road.

tctnd · 03-20-2005, 11:24 AM

What you have is an example of galling. This occurs when a tiny bit of the aluminum head bonds (welds) to the plug through friction as it is unscrewed. Once it starts it just gets worse. This problem can be entirely prevented by the use of a little anti-seize on the plug threads. There are many old wives tales circulating to the effect that anti-seize will disrupt the heat flow and cause the plugs to run too hot or too cold. This is patently nonsense, but even if true could be easily dealt with simply by using a different heatrange plug.
You may get by simply chasing the threads if they are not badly torn up, but will probably need to have an insert installed. This is best done on the bench, but given the expense, can be satisfactorily performed in situ by someone who knows what he's doing. If you go this route be sure that the tech knows his stuff because failure means the certainty of engine removal and breakdown.
regards,
Phil

coloradoporsche · 03-20-2005, 12:36 PM

Hey Everyone,

Thanks for the responses. I really appreciate the help. If I do decide to take the head off, do I need to drop the engine or can it be done from above?

Nitrometano · Nitrometano's Garage

Remove the valve cover and the engine sheet metal from that side. You will gain some space. Indeed if you need a more space. Put a jack and towers under the engine and loose it from the engine mount. Down the engine a bit. Be careful.

H20911 · 03-20-2005, 01:55 PM

If you do chase the threads with a tap put a little grease on it to grab bits. also take your time and clean the tap completely several times adding fresh new grease each time. Oil might let some of the bits get in the cylinder. Obviously not really a great option but if the damage is not too bad you might be okay with it without the tear down.

Lastly anti-seize is your friend.....a good friend indeed

.

prooutlaw · 03-21-2005, 04:21 AM

Very well put Noah.

porschenut · 03-21-2005, 05:35 AM

No way you can pin this on the seller.

coloradoporsche · 03-21-2005, 07:21 AM

Hello,

As you can tell from reading my original post, I did not know what galling was, so please give me a little slack here. My assumption at the time of the original post was that the plug must have been jammed in with about as much force as it took to get out

Thanks to this forum, I have a much better understanding up what may or may not have happened to cause this problem.

I don’t think my reaction was atypical for somebody that bought a car and then finds a potentially serious problem the first time they change the plugs. All I said was that the seller seemed honest, and the feedback here has confirmed that he probably was. So, I don’t feel that I slandered anyone. (slan·der: A false and malicious statement or report about someone) A simple "I don't think the seller knew" would have sufficed.

That being said, I really do value the feedback with regard to the seller's probable innocence here. It gives me some peace of mind and I appreciate you guys addressing that issue.

Thank you.