Spark Plug dilemma

[carreradpt]

85 3.2 #6 cylinder. I had a plug back out on the road not far from my house, so I did a roadside fix and drove back home. Never seen that before. Those plugs have been in there for about 6K miles. When it cooled off I pulled the plug and it looked OK, no thread damage or any extra stuff on its threads. I grabbed a new plug and it started into the cylinder fine for about 4 or 5 turns and then it just stops. It will not go further and I am afraid to force it. I back it out and remove it and try it again. It goes in easily and turns easily and then just hits a stop. I am positive I have not previously stripped any threads as I would never force it.

What should the next step be? Of course I can't see a thing in there. Do the threads need a "cleaning", could carbon have fouled the threads?

Thanks for any guidance. DT

[DRACO A5OG]

Yes, that could have been the reason it popped out because it was not seated all the way in and now obstructed by carbon build up.

You may need to tap a threader in there to dislodge the carbon and use copper anti-sieze.

I had to tap my 190e when I rebuilt the cylinder head.

[carreradpt]

Draco, when you tapped it did you worry about crap being pushed into the cylinder? Or do some taps force the stuff backwards?

[carreradpt]

Is a thread chaser the same as a tap? Anyone have experience with this particular issue?

[DRACO A5OG]

Yeah it will toss derbis into the head. I had the cylinder head off when I did it.

Let's try something else, how about a swab same diameter of the plug douced in carbon cleaner and try cleaning it out then places some anti-sieze and try threading the plug in again?

There's got to be someone who had similar issues.

Just a thought are you sure you are going in straight and not cross threaded?

I recall #4 is a real biotch with the comnpressor in the way.

[carreradpt]

I am absolutely sure that I am threading this thing in correctly. 6 is pretty easy to get to. It threads so easily until it hits a wall and I have not tried to force it past. And it turns maybe a third of the way easily then stops.

I like the carbon cleaner idea. Have been reading up on thread chasers and I think that is the route I will try, carefully. 14 mm thread. With some carbon cleaner. Thanks for the suggestion. Will look for both tomorrow.

Ever used a thread chaser?

[DRACO A5OG]

Yes, I have, I also used wire brush flute

[ancashion]

You've probably already done this but I would check the threads on the new and the old spark plug. Maybe the new one or the old ones threads weren't machined correctly. Maybe the thread pitch isn't the same. Did you try a different new plug? Did you try to swap in a used plug out of a different cylinder?

[DRACO A5OG]

BG44K is even stronger, don't get it on the paint, it will melt.

[jrolstin]

FWIW, we used a helecoil kit at the track on one of our formula vees. Motor was in the car. Air cooled flat 4... still porsche as far as I'm concerned (if that helps). This was done because the spark plug blew out on the track due to weakened metallurgy.

[manbridge 74]

If you use a chaser, put some grease in the flutes and it should catch most debris. Perhaps if you get piston near TDC you can creatively blow whatever remains back out with air connected to a small hose.

In a pinch, one can also make a chaser with an old plug, cut-off wheel, and the correct die.

[Url]

Search on Back-tap, that's what I used!

[carreradpt]

Tony, I have put in a couple of different, same wrc7 plugs and they all do the same thing. Completely normal feel and fit by hand as it turns and then it just stops. So I am sure the threads are OK. What else could be blocking it if not carbon?

Draco, i'll see what I can get my hands on to melt the carbon. BG44k

Manbridge, i'll include that in my plan, thanks.

Back tap I read something of that last night. They used it on a cylinder that had the first few threads stripped so they started where the threads were good.

Thanks all.

[carreradpt]

Here's my plan. With a plug partially installed i'll use air to blow the area clear. I'll rotate the engine to TDC on that cylinder. I found a new 14mm spark plug hole thread chaser, i had some marvel mystery oil laying around and some wheel bearing grease. I'll put some grease on the end of the chaser and along the flat side of the chaser. Not sure what use I would have with the mystery oil though. Thought of using it to loosen the carbon. Hopefully this will work. Then i'll use a vacuum attachment and try to clean out the stuff, if any, out of the cylinder. Maybe air with a small tube.

Remember I don't believe I have any thread damage. So I don't think this will make things worse. Right???

Sound like a good plan?


Thanks

[Neel]

Originally Posted by carreradpt

Here's my plan. With a plug partially installed i'll use air to blow the area clear. I'll rotate the engine to TDC on that cylinder. I found a new 14mm spark plug hole thread chaser, i had some marvel mystery oil laying around and some wheel bearing grease. I'll put some grease on the end of the chaser and along the flat side of the chaser. Not sure what use I would have with the mystery oil though. Thought of using it to loosen the carbon. Hopefully this will work. Then i'll use a vacuum attachment and try to clean out the stuff, if any, out of the cylinder. Maybe air with a small tube.

Remember I don't believe I have any thread damage. So I don't think this will make things worse. Right???

Sound like a good plan?


Thanks

Sounds like a good plan.. I've this happen many times over the years. Proceed slowly, you should be fine...

[Url]

Less risk for anything to fall into the cylinder with a Back-tap:


You insert it completely into the cylinder, twist it so it opens and start threading backwards... Works like a charm!

[Ruflife]

Originally Posted by carreradpt

Here's my plan. With a plug partially installed i'll use air to blow the area clear. I'll rotate the engine to TDC on that cylinder. I found a new 14mm spark plug hole thread chaser, i had some marvel mystery oil laying around and some wheel bearing grease. I'll put some grease on the end of the chaser and along the flat side of the chaser. Not sure what use I would have with the mystery oil though. Thought of using it to loosen the carbon. Hopefully this will work. Then i'll use a vacuum attachment and try to clean out the stuff, if any, out of the cylinder. Maybe air with a small tube.

Remember I don't believe I have any thread damage. So I don't think this will make things worse. Right???

Sound like a good plan?


Thanks

You may want to remove the upper valve cover - remove the engine shet metal on the side - and drop the motor down 4 or 5 inches to get a better perspective while doing the fix. At least that way you can guarentee your going in the plu hole square etc.

[lindy 911]

What are you using to install the spark plug? Some plug sockets will bind on the cylinder head giving the feeling of stopping. Use a 12" piece of 3/8 rubber fuel line and push it on the end of the plug (where the wire cap would go). Using the hose to hold the plug, twist it in and see if it doesn't go in all the way. Once it's in use a socket to tighten. Keep your fingers crossed...

[carreradpt]

Here's an update. I did remove the valve cover and gasket to help get me closer. The thread chaser started fine and then hit the block. So I backed in up a couple of turns then went a little farther. There was a bit of resistance but not much so I continued like this, back and forth for a few hours. Back the chaser out, clean it up, regrease and reinsert. Seemed to be working perfectly. Then it "broke thru". So I backed it out and cleaned it up. There were real fine pieces of aluminum on it. I then put a small tube on my Vac and Vacuumed the area and the cylinder. I was certain the plug would reinstall. It did not.

I can not get the plug started now. I tried to reinstall the chaser and I could not get it to start threading either. Crap! Spent all day on this, taking my time, certain that it was not screwing up the threads and just cleaning up carbon out of the threads.

So here I sit pondering my next step. I talked with my local Porsche mechanic late yesterday and he said that the only thing now to try is a plug tap. If I took it to him, that's what he would do. Same way, lots of grease to trap aluminum and take it slowly. If that fails then it gets expensive.

So my question is; How should I proceed now? I do have a Plug Saver M14-1.25. Is a back-tap a better choice? Anyone have experience doing this with the motor in the car?

Thanks again for any help. Dan

[porwolf]

Sounds to me that a "plug tap" might be the answer. I have re-taped quite a few threads, though not spark plug threads. a"plug-tap" maybe tapered like other ordinary taps. A tapered tap will start much easier because it engages on deeper treads. A straight tap like the one in the picture above will try to engage in the first threads. I don't think that you did any serious damage. It sounds like just the first and/or second thread is somewhat out of line.