Things have taken an unpleasant, new turn. Last night at 55 mph, the usual fluctuating valve condition blossomed into an intake valve sticking open and resulting in the sound of exploding combustion coming from under the hood. The vacuum gauge wired to my dash went wild. It was intermittent in proportion to the amount of gas pedal I was feeding it. After a mile or two, the explosions went away and I was able to limp home at reduced power. Perhaps I should have pulled over to the roadside and just sat there with the hood up instead of motoring on, but having no cell phone with which to call a tow truck I kept going. This is the first time that intake valve(s) have been affected versus exhaust.
So now I'm back to Pre68Dave's question about oiled rockers. As I mentioned earlier, I changed out the rocker arm shaft that broke last year with a used one. The actual wear on the used shaft is about .001" rather than .002". The front 1-3 cylinder rockers (new shaft) all oil nicely and evenly at idle. The back 4-6 cylinder rockers (used shaft), not so evenly. #6 intake flows like crazy while #5 exhaust barely at all based on the amount of oil exiting the top vent in each rocker. The re-builder pinched off the tube on the center oil connector to boost pressure to the rockers. I disassembled the rocker arm and shaft assemblies today to make sure that they were identical on both sides, Both new and used shafts have the slight flat milled surface on the bottom. I noticed that the inner oil groove on #6 intake lines up with the pressurized oil hole in the shaft explaining the mini-geyser of oil coming from that vent hole. I cleaned out some crud from the vent holes of the other 4-6 rockers and they oil better now. Is it normal for #6 intake to flow a lot more than the others? My new theory is that partially blocked oil flow to the rear rockers could be responsible for them seizing up at high speed when hot and causing the valve havoc. I've noticed before that there is increased lifter/pushrod noise when the engine is acting up but maybe that's because the rockers are partially frozen.
Does this seem likely?
After almost getting stranded on the interstate last night, I'm now reluctant to take off on a long journey without having changed anything substantial on the engine.
