Bad news for the 1980 POS

[PRattenbury]

Well, I knew the engine had some sort of malfunction since it got back from the tranny shop. But I needed the truck to get to work with, so I drove it. Anyway, I finally got around to doing a compression check on the engine. The same engine I spent all sorts of time and money on this past winter, putting in a cam, lifters, timing chain and gears, intake, carb, heads, MSD ignition, blah blah blah... All my cylinders are 100-120PSI, except for #1, which has 45 PSI. I took the valve cover off, put my fancy 'window' valve cover on I use for setting valves. Started the engine, watched the valves on #1. Everything looked fine. So I backed off the exhaust valve rocker till it clicked, tightened it till it was quiet, then gave it 3/4 turn more. Did the same for the intake. Put the real valve cover back on. Hooked the compression gauge back up. Cranked it again, still 45 PSI. Am I dead? I get angry clattering noise in upper RPMs just before a shift. But I don't beat on it. I'd guess the RPMs are 4000 maybe when I hear the clatter. Engine runs like ass. No cajones at all. All the plugs look good to me. Nice light grey color.

[69subaru360]

Do a leakdown test and see where the air comes out.

[PRattenbury]

I'm thinking I either have a burned valve (which would piss me off since I just put new heads on this past winter) or a piston/ring issue. Either way, I'd have to at least pull the head on the driver side. If I'm gonna do that much work (again), I'm gonna rip the whole deal out and put a GM Performance 350 crate engine in and be done with it. 2 grand, and I'm done. But I guess I gotta get the old Cummins running againand put the POS Chevy back in the garage for the winter. What a friggen load this truck's been...

[dccarpenter]

No advice on the technical side of things but I can relate with how you feel about it..I've been stuck before with 3 vehicles and all decided to act up at the same time, some of them after I'd spent money and more importantly a ton of time trying to keep them running.

[Cherub]

If its a piston ring it would smoke.

[nbpro]

Originally Posted by 69subaru360

Do a leakdown test and see where the air comes out.

After doing a compression check, if one or more of the cylinders tests low, then a cylinder leak down test will help you determine the cause of the weak cylinder. Special equipment (leak down gauge) is required which can be purchased at most auto parts stores. With all the spark plugs removed, rotate the engine so that the cylinder to be tested is on top dead center and ready to fire. This will assure that the valves are closed. Install the leak down gauge in the spark plug hole and apply air pressure. The gauge will register the pressure drop indicating the percentage of leak. In addition, by listening at the exhaust pipe or air intake system or the oil breather you may hear escaping air, which means one of the components, is leaking. Example: air out of the exhaust pipe means the exhaust valve is leaking. By removing the radiator cap and observing the coolant, you can tell if there is a blown head gasket and or a cracked head if there are bubbles.

[primrrd]

chev engines in this time frame were bad about wearing certain lobes down on the cam. possible this might be what your dealing with?

[PRattenbury]

It is possible the cam ate a lobe, but not likely. I replaced the cam this winter. Which would seem to increase the risk of a bum lobe. But I did pull the valve cover off, install my special 'window' valve cover (no top on it) started the engine and observed the operation of the rockers. They are moving up and down like everybody else. I even readjusted them just for grins. I then rechecked the compression... 45 PSI. I put a vacuum gauge on it and it's steady 22 or 23 inches at idle. No dancing needle. So I'd guess it isn't an intake valve. It sounds to me like an exhaust valve issue, but it could be a piston/ring issue. Either way, I am unwilling to invest the time to figure it out on a tired 307 block (other than posthumously). I was stupid to mess with it in the first place. Now I'm paying the price. I ran a risk, and lost. Stupid hurts.

[LONGHAIR]

Try squirting some oil down into that cylinder through the sparkplug hole and re-testing. If it has a ring problem the oil should make it "temporarily" better, for testing purposes.