Yeah, I concur, Best case you won't strip the threads, just muck 'em up a bit. Then you can just get a tap and chase the threads. Worse case, you get a starter tap with some cutting oil and a t handle and retap the threads. If you do that, just remember the threads won't be as strong because you are keeping the same size, There is not enough material to put the same amount of torque on the threads, just make it snug.

There is always a worse case. And that is you might have to go to a timesert. AKA thread repair.

Haha, ain't that the truth!

I'm looking at it like this. If it ain't broke, don't fix it. The passenger side pre-cat O2 is the one stuck but it's also the one not causing any issues. So I don't see any reason at this point to go muck it up if I don''t have to. If I need to in the future, I cross that bridge at that point.

We this doesn't sound good. I ran the compression test today and here are the results:

driver side starting from the front of the engine: 55psi, 54 psi, 120psi & 120psi.

passenger side: all came in around 180 psi.

I don't know how to interpret these results but I'm pretty sure it's bad.

I've already pulled the driver side valve cover off and I've attach pictures of the driver side spark plugs and pictures after the valve cover were removed.

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Could it be the oil pressure releif valve in that head has stuck causing too high pressure in the hydraulic lifters?

Did you run the test correctly. Like in TDC? Is this the engine with the loose valve cover?

Or is that leakdown test? Yea it is. Um 55psi in two cylinders. Very strange.

With the engine warm, I took off all of the ignition coils and spark plugs.

I had my son turn the ignition until it cranked 4 to 5 times.

I retested the diver side to make sure the readings would be the same, they were.

Is it possible that valve adjustment is due? Can a valve adjustment be done on an X5?

Youtube leakdown test. watch a few videos. If you have the compression test tools, the next step can be done. You need to test if your valves are leaking.

Did you have smoke before?

[QUOTE=SlickGT1;897845
Did you have smoke before?[/QUOTE]

Yes, I did, no leaks.

I will google the 'leak down' now.

Would you suggest running the compression test again using the oil in the cylinder trick to determine if its piston rings -vs- valve or head gasket. Or will the leak down help to achieve the same conclussion.