- Turns out not one but two pushrods were bent (both on the affected cylinder) - not surprising, what with nowhere for the expanding gases to go when the exhaust valve wasn't opening. (This would explain why I was getting low temperature readings on that part of the exhaust header, as well... more on that in a moment.) But it is surprising when assuming the bending happened while trying to get the new digital MSD setup to fire. My oh my am I glad that I purchased a full set of new pushrods instead of just one. The intake pushrod on the #7 cylinder was bent into such a curve that I had to use a Vice Grip to straighten it enough to remove. Yowza. And as soon as I pulled it out, the ball-end that sits in the lifter just dropped out onto the floor. Thank the Gods of Internal Combustion that it didn't fall off inside the engine when it was running, or this would be a tragic post.
- I removed the full rocker-arm assembly, so I could check the other cylinders' valvetrain, as well. Thanks again that they're all fine.
- The little balls on the ends of the roller-rocker arms (where the cup-ends of the pushrods fit) were pretty galled up, so I had to grind them smooth. The underside of the aluminum rocker for the exhaust valve was really marred, too, but the bearings appear unharmed. Clearly, now, evidence pointed to the engine having run with bent pushrods for a good long time. Eep. (On the plus side, I can't wait to see what kind of power it puts down with 8/8 of the engine running instead of 7/8.)
- I put everything back together, properly assembly-lubed and anti-seize-lubed as appropriate, then torqued as appropriate. Then I went through each rocker-arm assembly and individually set the lash at "pushrod just barely spins when tightened down," as directed for a hydraulic lifter setup.
- With everything buttoned up, I manually rotated the engine through a full 360°, so I could double-check the valve lash before sealing up that valve cover - never assume everything is correctly adjusted after just one set of tests.
- Surprise! The exhaust pushrod on our friendly #7 cylinder? It was sitting loose in the head. How could this be, as I had carefully adjusted it? Well, I loosened the lock-nut, then turned the ball-stud bolt where the pushrod rests on the rocker-arm... and discovered that it wanted another half-inch of adjustment. Now, I may not be perfect at adjusting everything the first time, but a half-inch off? It had just the right amount of rotation when I locked down the nut just a few minutes prior. So I checked the pushrod length, and it's not a half-inch shorter than the others.
- What does that leave? Collapsed lifter is what.
- The rocker-arm could be so badly chewed up.
- Early tests with a temperature-gun showed #7 to be running cool: Non-firing cylinders don't get hot.
- The engine always ran a little ragged - I had assumed it was just the semi-radical cam.
- The timing was so hard to get right.
The first sign something was wrong....
So the car will not be ready for Saturday's car show. Sadness. On the plus side, the broken lifter won't cost much to replace, just a huge amount of time: This task requires pulling off the AC unit, the intake manifold, the valley pan, plus all associated hoses, wires, throttle cables, and so forth. Not a one-day job. On the other plus side, forecasters tell of guaranteed rain on Saturday, so the show might be a bust, anyhow.
Now, off to class. More later -