So I pulled the valve cover, everything appears to be moving as it should and the piston is going up and down... all the valves are opening and closing, how could there be zero compression? Rings? Did my compression tester just decide to stop working after testing the first 5? I'm lost. Gonna put the valve cover back on and try again with some oil in the cylinder I guess but I don't understand a 0 reading if everything is moving as it should...

 

The valves moving up and down doesn't prove that one is not burnt or being held open (such as from a "pumped up" lifter, or incorrect adjustment if you have adjustable valve train).
And/or you could have stuck piston rings. Although usually some compression will show on the gauge.

A "cylinder leak test will tell you where the compression is going. There is a tool for this (naturally) but in a pinch you can simulate the tool. But you need an air compressor

Here's how it works:
1) Rotate the engine so the cylinder tested is on its compression stroke (the distributor rotor will be pointing the that plug wire on the cap).
2) You remove the spark plug and loosen the rocker arms (to be sure the valve are fully closed).
3) Insert your "test fitting**" (its like the compression gauge fitting) into the cylinder where you can put compressed air into the cylinder.
4) Blow air into the cylinder.
5) Note where the air exits. If it comes out the crankcase breather the piston rings are leaking, if it comes out the tail pipe the exhaust valve is leaking, if it comes out the carb the intake valve is leaking.

** Test fitting. You can use part of your compression gauge if it has the removable thread ends for using with different size spark plug holes. You put a fitting on it that connects to your air compressor line. You need a shut off **** in bwtween so you can slowly open the valve to let air into the cylinder. Adding air too fast (or too much pressure) can just rotate the engine.

Some air leakage into the crankcase is normal (the tool will tell you want "percentage" of air is leaking) the home made tester would not, so in that case you would need to decide how much leakage is a problem.

 

I didn't have the materials to attempt a leak down test and with Georgia summers and a metal garage I haven't been messing with it for a minute. I took the head off today and everything looks good, I put some oil in the cylinder to see if it would seep down and it didn't. All the cylinders look pretty good, the one thing I noticed is that while all the exhaust valves are a nice golden brown color the one on #6 is black so I assume it isn't seating properly... am I correct in assuming this is the cause of the 0 compression?

 

Have you tried gas over the oil? Oil may be to thick and would not leak past a bad valve.
Dave ----

 

Sounds like timing is too advanced... easy test would be to loosen distributor just enough where it can be turned by hand but not on its own. Unhook electrical or vacuum advance and start engine. Turn distributor slowly clockwise first and see if idle smooths out or gets worse... then go country clockwise and see if there's a sweet spot. This will at least give you a reference. Also I would replace rotor and button, thinking the timing is retard do to bad rotor could cause you to over advance. Or start over and bring number one cylinder to top and line distributor up with number one then repeat clockwise counter clockwise

 

This thread is a year old