Compression Check??

What should the compression be for a series 2 SC? Per cylinder.

The last one I checked had 140,000 miles. On a cold engine, 148-150 psi per cyl. They should all be within 10 % of each other. A fresh engine will often have 175-180 psi. Trust me, you want a cold engine to do this.

pbrktrt wrote:

The last one I checked had 140,000 miles. On a cold engine, 148-150 psi per cyl. They should all be within 10 % of each other. A fresh engine will often have 175-180 psi. Trust me, you want a cold engine to do this.

OK thanks for the help.

All six cylinders read about 148 psi odometer reads 123171 definitely not what's on motor. But since so close to what you posted I will assume it 140k+
Thanks again for your help greatly appreciated!

FERGI'S 97 SC RIV wrote:

All six cylinders read about 148 psi odometer reads 123171 definitely not what's on motor. But since so close to what you posted I will assume it 140k+
Thanks again for your help greatly appreciated!

If all 6 are 148 +/- you are in decent shape.

pbrktrt wrote:

The last one I checked had 140,000 miles. On a cold engine, 148-150 psi per cyl. They should all be within 10 % of each other. A fresh engine will often have 175-180 psi. Trust me, you want a cold engine to do this.

I am reading that the engine should be warm when doing this?

charlieRobinson wrote:

pbrktrt wrote:

The last one I checked had 140,000 miles. On a cold engine, 148-150 psi per cyl. They should all be within 10 % of each other. A fresh engine will often have 175-180 psi. Trust me, you want a cold engine to do this.

I am reading that the engine should be warm when doing this?

Absolutely. You want normal operating temps so that everything is properly expanded. Piston rings and pistons expand when hot. You also want the throttle blocked open, ignition disabled, and all spark plugs removed.

Just to remind everyone for the 1,000 time. I'm almost a total newbie to cars.

Ok, what about fueling? should the pump be disabled also?

charlieRobinson wrote:

Just to remind everyone for the 1,000 time. I'm almost a total newbie to cars.

Ok, what about fueling? should the pump be disabled also?

Yup, forgot about that. Disable the fuel pump. If you are that green when it comes to cars, just pick up a basic book on Auto Mechanics.

Is it normal for a well maintained engine to naturally lose compression over time/use?

charlieRobinson wrote:

Is it normal for a well maintained engine to naturally lose compression over time/use?

Yes....

If you use synthetic oil 9specifically a PAO-base oil) exclusively and keep up with changes it takes **A Lot** longer. But eventually it will wear. With Synth it is almost anyone's guess as to how long "eventually" is, someone on here might know. IIRC our member AA found that even after hundreds of thousands of miles running "dino" oil (group III natural base) with oil changes often-enough, the crosshatching was still evident in the bores. I have heard it's not uncommon to tear down an engine maintained with synthetic oil only to find that wear is not measurable using garage-quality measurement tools... but I've never done it.

For those of you who like chemistry/tech: Polyalphaolefins (PAO) are also called synthesized hydrocarbons and consist of a single molecular structure, usually manufactured by reacting ethylene gas with a metal catalyst. They contain absolutely no metals, sulfur, wax or phosphorous. Metals (zinc) are added as part of the additive formulations for making motor oil. The big advantage of PAOs that they function over a broad temperature range and don't have trace crap in them that has to be refined out or compensated for. They also hold lots of contaminants in suspension further reducing deposits.

Quote :

IIRC our member AA found that even after hundreds of thousands of miles running "dino" oil (group III natural base) with oil changes often-enough, the crosshatching was still evident in the bores. I have heard it's not uncommon to tear down an engine maintained with synthetic oil only to find that wear is not measurable using garage-quality measurement tools... but I've never done it.

That's about right, according to the report from my re-builder. I didn't actually see the bores myself. He said all bores were perfectly circular, within spec (did not need over-boring). I don't know if the crosshatching was still visible, but there was enough wall material that he was able to re-hone the cylinders without needing to machine. At the time of the rebuild, the engine was still making good power, and oil consumption was about 1 quart per every 3k miles.

So i am doing a compression test on my buick riviera supercharged 1996, anyone know what kind of compression would be accurate around 150k miles? i was thinking anything above 150 would be good but does anyone know exactly what they come with from factory?

as long as you see relative consistency, the exact number isn't that critical. 150 is a good estimate.

Awesome thanks!