Compression test problems.

[blhickson]

In another thread, I had a cooling concern and vinegar flushed, removed and tested thermostat and while it was out, vinegar flushed again. Everything is checking out fine EXCEPT...
Compression test checked out after warming up these numbers: 0/90/90/120.
I did not have any MMO put the last in the fuel tank put motor oil in cylinder 1. I replaced the spark plugs. The engine seems to run fine altho still seems to "hunt" during idle but now what? Compression test again? Kinda bummed, in 2009 all numbers were 115 to 120.

[hanleyclifford]

Usually zero compression suggests a hung valve. Try removing the spark plug and inserting the end of a long allen wrench into the cylinder to push the valve down. Listen for a light snap.

[pindrums]

Allen wrench

Don't let the allen wrench slip down the hole (like what happened to me). Couldn't fish it out, so out came the engine!

[Al Schober]

You can also move the valve by pushing from the bottom. Put a feeler gauge between the tappet and the valve stem and turn the crankshaft. The tappet will then push the valve up slightly, perhaps enough to loosen it up and allow some PB Blaster to work it's way in. Don't overdo it.

[blhickson]

I put some MMO in the cylinder and let it sit for a day and retested. Got 90s on all 4 cylinders. BUT I think in the first test there may not have been enough juice in the batteries for a conclusive compression test. They wouldn't crank when I I tried to retest and had to use a charger to get batteries up to power. Oh well, 90 is better than 0. And the engine runs smoother than ever.
Thank you to everyone for the great intel. I'd be lost without this forum. Does anyone know the thread that defines the symptoms of what ails cylinders and the head gasket? I've looked and read and can't seem to find one. I think the head gaskets need replacing. There is an oil leak under the oil pressure sending unit, not from the unit itself, under it where the two pieces of the head ? Or manifold ? Come together. I cannot find in the manual what exactly is the head, and the manifold.

[BunnyPlanet169]

The head is the casting on the top of the engine, and has the spark plugs screwed into it. It is the top, or 'head' of the engine, and sits on top of the block. It's about 1.75" thick, and underneath it you'll find a crack all the way around like a bathtub ring which is where the head gasket takes up about 0.06" thickness.

The manifold (in our A4 world both intake and exhaust combined into one casting) is mounted on the side of the block. It has the carburetor mounted to it underneath, and the exhaust exits to the rear (usually). That gasket is harder to see because of the shape of the casting.

Underneath the manifold, behind the carburetor, there is also a flat cover over the valve springs. That can sometimes seep oil as there's only two screws holding it down, and not a lot of pressure.

Underneath the oil pressure sender, the flywheel housing and the block join the oil pan. Those are major castings, and difficult to seal short of pulling them apart. Let's not go there yet...

Pictures?