Ran a Compression Test. What now?

[BrentBTK]

Greetings all. I've only had this truck about 2 months, and am still getting to know it. I'm not real happy about the low (8ish) oil pressure at idle and there is definitely a knock that I suspect is a rod or lifter, but I'm not sure. I'm sure it's old and tired, but I have no idea what has been done to it. Today, I ran a compression test to see if there were any glaring differences. While I did not see any wild variances, I am a bit concerned with what I did find:

1:95 2:97
3:93 4:90
5:97 6:90
7:95 8:90

Does that seem generally low? What's interesting is I expected 1 or 3 to be significantly off, the knock seems to be in that area and there is a lot of oil and sludge on the side of the engine by those cylinders. The passenger side is nice and clean. I'll admit I don't really know what is "good", I'm just trying to figure out where I am. Thanks! Edit: It's a 350

[BrentBTK]

Disregard. I'm a dumba$$. I failed to hold the throttle open. Back to try again!

[mattfranklin]

:-)
We all make mistakes.

BTW, I wouldn't judge cylinder health by external leaks and crud. But what you could do is look at the spark plugs.

Rods would make more more of a kung-kung-kung sound.
Valvetrain would make more of a clattering or tick-tick-tick sound.

Heavier oil might help with oil pressure and rod noise.
They used to say 10 psi per thousand rpm was a good ballpark number, but mine's got a full new bottom end and is much higher than that.

Originally Posted by BrentBTK

Disregard. I'm a dumba$$. I failed to hold the throttle open. Back to try again!

[MySons68C20]

Is your compression tester a known good one? Your numbers look fairly consistent which is good but the numbers do look low.

[BrentBTK]

Well, I tried to run it again, got 110psi on the first cylinder then the tester crapped the bed. Won't read anything. Changed the plugs and buttoned it back up. The number 1 plug looked a little fouled, but not terrible. The rest were dry and kinda rusty. The knock definitely sounds heavier than valvetrain. It sounds like one rod banging. Gets louder as it warms up and consistently follows the RPMs. I put a quart of Lucas in it, didn't help much. I've been half way looking at new crate engines. If I'm being honest, I'm probably looking for an excuse to pull the trigger. This is my daily driver, and I want to start from as much known good as possible.

[Dead Parrot]

Take all of the belts off and listen. Without the fan and accessory noises, all you will hear are the engine and exhaust noises. You can't run it more then a minute or so due to no water circulation. But that is long enough to notice if things get a lot less noisy. If the knock goes away, suspect a power steering pump. The PS pump is next to #1 and 3. Exhaust leaks can sound like engine noises, especially if the leak is in the intake crossover.

[crazy longhorn]

Agree with DEAD Parrot... & will add. On the ex noise, get a 3ft long pc of heater hose.....you can put that up to your ear, & take the other end around the ex ports. You will hear it if they leak IMHO, that engine should kick around 140-150 psi on cranking pressure (fresh). That said, get a new comp checker.....if she runs smove/no smoke, you may be good to go for a while. On the oil pressure issue, it takes around 10 psi @ idle to keep the hyd lifters up(stock engine), or very mild cam. I will ask.....the 8 psi, is in park, or in gear? Longhorn

[BrentBTK]

Thanks for the tips, fellas. 8 psi is once its warmed up and in gear, about 650 RPM. If the valve covers are to be believed, it's had some work done from RHS Performance Engines in Tennessee. I have no idea if it was just head work or what. Other than the knock, she has a decent lope. I'll do some more investigating tomorrow after i get a new tester. Maybe a leak down test would be a good idea? Never done that either, but I'm learning!