I got a big issue and I just don't know.https://rennlist.com/forums/graemlins/soapbox.gif
Changed out the plugs, rotors distributors and oil / filters, trans / filters and fluids / lower valve cover gaskets, and one side of the LHS timing chain cover, bolts and gaskets on my 95 / 993. All went well until I got to the last plug, the RHS upper, it was a bear to get out, and when i checked the condition it was thread scared, mostly on the tip. When I went to put in the new plug it never seemed to grab. Now I am looking at it and saying what does one do now. I am looking at something I am not sure of my next step, do I take the upper valve cover off and insert the plug?
Any sane Idea would be appreciated, needless to say I always want the easiest way out.
In advance thanks for input.

Mike Smith
95/993 Cab with 97,628 miles, trip trans.

 

My next step would be to try to figure out what the condition of the thread is in the case. Shine a flashlight in there and see if you can see. If you have a boroscope stick in in and examine the threads. Can you post a picture of the threads on the removed spark plug?

It may be nothing to be concerned with. I have at times had trouble mating the plug with the case threads as the angle needs to be just right. Keep trying. Also, it helps to use a magnetic socket.

 

Very good advice posted by Vorsicht (Peter); especially the photo of the plug that was removed.

A bore scope would be great in this instance, as it would enable one to see the condition of the existing threads, and whether they could be saved by chasing them with a thread chaser (not a tap!) in the event the internal plug threads were galled.

If the threads are galled, I would place the #6 piston just below TDC on the exhaust stroke and coat the thread chaser in wheel bearing grease to potentially catch any aluminum bits that may release.

Subsequently, I would clean #6 as well as possible with;

1. A small screwdriver and lightly greased towel inserted just past the full depth of the plug bore, and press the greased towel against the plug threads and counterclockwise rotated, till it followed the threads out.

And

2. Use compressed air and some carb cleaner (sparingly) blown into the plug hole. Hopefully, any alum bits that were not captured by the grease, will be blown back out the plug hole or exhaust port, which should be open.

Once happy with the clean, squirt a small amount of engine oil into the cylinder to lube the bore and rings, and again some compressed air to disperse the oil.

Insert new plug.

p.s. Dont beat yourself up over this, Mike, as chances are this issue was created by the last person who changed the plugs...

HTH

 

Good news and bad news, the plug hit the trash when I took it out, or at least a few days later. The "tune up has taken awhile".

The threads as I best recall where damaged on the bottom an appeared to be heavily misshapen and made smaller, as if they were forced into place and crossed, the top of the threads seemed to be okay where they would have been seated against the head. Which would indicate that the internal damage was on the beginning of the cylinder head and the bottom somehow grabbed and held until I took out the plug.

I do not have a bore scope.

I have seen in other posts a thread chaser, with the upper # 6 as the issue and the length of the spark plug tube, is it the correct thing to take off the upper cover and go after the work from there?

The issue I have is doing the thread repair with the engine in place and the angel of attack, the metal filings and anything else that can go wrong.

 

Got IT in, with no issues a little tight with the last 2 to 3 turns but sitting nicely.

Took the top valve cover off after figuring out how to get the top bolts on the upper right side of, (thank God for pictures). Could actually see into the cylinder head, with mirrors and a flash light, threads did not appear to be damaged, cleaned the threads and saw no metal wires or pieces, blew it out and set the plug by hand until I could not turn it any longer, now off to reassembly. thank you guys for the help, it was greatly appreciated

Mike Smith

 

Mike,
If things looked as good as you indicate, I would have for sure ran a thread chaser into the plug hole to clean things up.
Cheers!

 

Good for you! Crisis averted. Next time I would do as Nine9Six recommended above (chase the thread). That way you know you have a nice, clean thread and it is easy to do.

 

Thanks, for the info.
Must have been a carbon build up or ?
Will do.


Mike Smith

 

Would this have potentially dropped debris from the threads into the combustion chamber potentially scoring the cylinder walls once running?

My experience is even if one "blows things out" debris remains.

 

Andy,
Curious as to what you might suggest? If you have existing galled alum plug hole thds in the head, the act of inserting another plug without chasing the them, could very easily roll an alum thd into the combustion chamber. Especially if the plug went in smoothly until the last few thds!

At least, when utilizing the other method, you have a chance of blowing any debris out the plug hole or exhaust valve; instead of potentially closing things up with alum thd remnants inside the cylinder.

 

I just finished this job on my '95.


Number 6 top plug was definitely a bear, but at least mine came out OK.
I made up a mixture of Wurth CU1100 + engine oil and gave my plugs a light coating. I used a magnetic socket and had to 'assemble' the socket + extension + mini ratchet together to get access. Turning the plug CCW so I could hear a 'click' helped to seat the plug properly and prevent cross threading.


Based on the limited access, I don't see how anyone could do thread repair or "chasing" on this cylinder with the engine in the car - and something I would never attempt.


Glad you got it worked out!

 

Looks like risk has no 100% mitigation.

 

True that...That's why they call it risk.
This is why I always choose some level of mitigation over none.

Cleaning those threads with a thread chaser just makes good mechanical sense, unless of course ones mechanical skills are limited, and the chance of making a bigger mess O' things is higher than the reward.

 

I am not sure if using compressed air in there is the best plan. You might push any swarf where you really cant get to it or see it. Its been a while since I looked at #6 but can you get near it with the hose from a shop vac? With the valve cover off? If I was going to attempt a thread chase operation with the engine in I would be trying to get some sort of camera up there to take a close look first. Maybe the threads are ok.