Compression Test on 200k LQ4 - Question on Results

[bsampson]

I have a 200k mile LQ4. I have it on an engine stand, and am planning to put in a new cam, lifters, lifter seals, timing set, oil pump, and rear and front main seals.

The engine has been sitting for over a year. Old oil is still in the pan.

I wasn't going to pull the heads, but after doing a compression test, I got higher numbers than expected. The compression tester is a new, $25 amazon tester.

Front of Engine
(1) 225 (2) 235
(3) 235 (4) 225
(5) 235 (6) 60 (260 after 1Tbs oil)
(7) 235 (8) 230

On cylinder 6, I test multiple times. It did hold pressure fine, just wouldn't pump up well. I went to lunch, and came back and it held 100psi for probably 45minutes. In subsequent tests, it seemed to increase and got up to around 150 psi. Once I squirt a little motor oil in the cylinder, it quickly went up to 260 psi. And held.

Question 1 - Does the high pressure mean I have a crappy gauge, or lots of carbon buildup?
Question 2 - Should I be concerned with cylinder 6?

[AussieinNC]

Those figures all sound high as though the engine has oil contamination in the cylinders, perhaps from being rolled over upside down and being left that way for a time.

The low cylinder, 60, makes it sound like bad rings in that cylinder.

If it were mine I would be pulling the heads while its on the stand and checking the bore wear patterns and look for broken piston lands on cyl 6.

Any bore ridge that you can feel with your finger nail would mean a bore job and new pistons and rings.

At 200 K miles, the valve guides and seals will need doing anyways, so you may a well bite the bullet and pull the heads...IMHO.

[Accelo]

Check out this posting. He had an identical issue. It was even on the same number 6 cylinder.
https://67-72chevytrucks.com/vboard/...mpression+test

[Factory Guy]

I had similar results on my LQ4 when I pulled the heads. The engine appeared very clean on the top end.

I did NOT do a compression test prior. However I am glad I checked by pulling my heads, as I found CLY 4 had an exhaust valve leaking and on CLY 6 the intake was not sealing, so I ended up doing a valve job on both heads.

[bsampson]

Thanks guys, looks like I'll be pulling the heads.

[bsampson]

I pulled the heads, and I don't see anything obvious, but I've only swapped heads one other time, and it was an engine with 40k miles, not 200k.

I see there is some carbon and oily crud that could be cleaned up. I did notice the gap between the piston on the upper part of the picture vs the top is not even. Maybe this is just the angle the piston is sitting in the cylinder at the bottom of the stroke? It's not so noticeable at the top of the stroke.

The circle towards the left side if the first image is a drop of water.

Does anybody see anything concerning, or advice on cleaning up the carbon? I was hoping not to have to take anything to a machine shop.

It held pressure really well in the compression test, so I'm confident the valves are sealing.