Cyl #4 70psi compression - ut oh

[3rdtimearound]

So I did a compression check on all cylinders after I bought the car rather than before. Smart right? Anyway all checked out above 150psi and in spec except for number four which was at 70psi. I then did a wet check where I added oil to the cylinder and it jumped to 210psi.

So this means rings right? Any chance it is just a head gasket? And what are my next steps? Do I need to do a leak down test or is this conclusive enough?

Assuming it is the rings is there a way to fix this cylinder without pulling the engine? Like push out just this cylinder with engine in the car?

Thoughts?




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[TobyB]

Just bought it? drive it a bit. It may have sat with #4 open, and have rust in it.

And don't panic immediately- while 70 isn't great, it's not a dead engine yet. Even
if something's wrong, you have time to find a replacement.

The #210 test confuses me a bit- usually with weak rings, oil boosts the number,
but not ABOVE the others- normal 'bad ring' numbers would see it jump from
70 to maybe 110 or something like that.

I'd investigate further- and keep driving it. Maybe a borescope, if you can find one to
borrow, or have a mechanic friend take a look?

Personally, I'd do a leakdown too, because it's cheap and easy. But I broke down and
bought a tester years ago...

hth

t

[3rdtimearound]

Cyl #4 70psi compression - ut oh

Some of the other cylinders hit 185-190 so the 210 isn't far off. Leakdown would be nice if I had the equipment.

Also I put 1000 miles on before testing it.

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