Welcome to the Forum.
You will find lots of help here.
Sorry that your first post has to be one in distress.
The value of a PPI can be immeasurable.
1) “
force the plug in and hope to get through the bad threads and find the real threads (seems like a bad idea).”
I agree – bad idea. This is probably what PO did and only a couple of threads was insufficient to hold the sparkplug. See if you can find someone local with a ‘bore scope’ to visually inspect the threads.
2) “
Attempt to chase the existing threads with a tap.”
You don’t want to use a tap. There are specific ‘thread chasers’ that rearrange the thread without cutting a new thread or making chips.
3) “
Try to do a timesert with engine in car. Not sure if this is possible.”
A Timesert isn’t the correct product. A Helicoil is the proper repair. This can be done in the car by someone skilled and experienced. It involves cutting new threads so all the ‘tricks’ need to be used. That includes removing the exhaust heat exchanger and doing the procedure with the exhaust valve open. Yes, you use grease on the threads, cut only a little and then remove the tool for cleaning and fresh grease. This still doesn’t preclude getting half way and needing to drop the engine.
4) “
Drop motor and do it right with a timesert. I am hoping NOT to do this because my workspace location is not ideal and frankly I really hate dropping motors.”
Clearly this is the best way. With the head in your hand, you can clean and inspect easily.
I recommend you remove and replace the other five sparkplugs first. If more than one feels incorrect, there isn’t any doubt that you should drop the engine. You might consider finding a honest and competent shop to do the engine removal and reinstall. They could store your car while you deal with the engine.
I recommend you do some more investigation before you commit to any path. You should do a cylinder leak test and cranking compression test. This will get you important information about the condition of the engine. I would remove the valve covers and put an Allen wrench on the head nuts. You don’t want to be surprised if there is a broken head stud.
Are there any oil leaks that should be attended to when the engine is out and easy? Use the opportunity to inspect the clutch; perhaps install just a new disc. Some regular maintenance like valve adjust, rocker arm shaft torque, etc. are easy when the engine is out. Certainly you will want to do some cleaning and detail work. 911 engines are a work of art.
Once the engine is out and you can inspect the #3 sparkplug hole you are going to have to decide whether to repair the head
in situ or disassemble the top end. There are pros and cons to each. Clearly it is more work and expense to disassemble even one side. On the other hand the job will be done the best possible.
How many miles on the engine? Is there any information of prior repairs, rebuilds, service, etc?
There are quite a number of Pelicans and PCA members in Boston area. What facilities do you have available? What mechanical skills and tools? This Forum can help you through almost any project.
Best,
Grady
