We're also not sure what prompted the removal of a cylinder head, but now that they're back on, try some more deductive reasoning to attempt to narrow down the cause of your latest misfire problem. You've had the heads checked by a machine shop, so we can probably assume that they're in decent shape. You said the car was running well at first, so you must have put everything back together in the proper place. You say there are no longer any coolant leaks, so your intake and head gaskets are probably alright, though you should verify the sealing. Check the crankcase, either by looking through the oil-fill hole in the valve cover or by pulling the cover. If the intake or head gaskets are leaking, oil and water are probably mixing, resulting in a white, creamy substance. If the oil looks normal, you should be OK. Spray carb cleaner or similar aerosol solvent around the intake sealing surfaces with the engine running to see if the idle is affected. If spraying the solvent results in a change in idle speed, you have a vacuum leak there, indicating a bad gasket seal. In the future, use quality intake gaskets along with a little RTV gasket sealer around the coolant passages.
The recommendation that you loosen the rocker arms may be heading in the right direction. It's pretty common for the rocker arms on small-block Chevy engines to be over-tightened during assembly. Unfortunately, if the car ran OK for a while but is now misfiring, there's a good chance that one or more lobes on the camshaft may be damaged. The factory hydraulic flat-tappet camshafts in small-block Chevys were fairly notorious for premature failure by the late '70s, and even those that didn't actually fail (causing some sort of backfire or miss) were usually nearly round after 10 to 15 years of use. If you over-tightened the valves, you may have finished off an already tired cam. But before you go yanking the cam, back off the rockers until they tick, as your mechanic suggested, and then re-tighten them just enough to eliminate the tick. If you don't like doing it with the engine running, shut it off and then tighten the rockers just enough to eliminate the clearance at the valve tip, and then go another 11/44 to 11/42 turn on your wrench. This must be done when the lifter is on the base of the cam lobe. If, when the engine is running, some of the rockers appear to move only slightly, figure the cam is wiped out-the perfect excuse to upgrade.
The Big ChillI live in one of the coldest places on Earth in Regina, Saskatchewan, Canada. It is not unknown for the temperatures to dip to about -30 degrees C-I don't know what that is by U.S. measurements, but it's still friggin' cold. Anyway, I have an '86 Cutlass Supreme with a four-bolt-main 350 Chevy motor, a 700-R4 tranny, and Hedman Hedders. I know that the cold can be very hard on vehicles. What can I do to minimize the damage that can potentially happen in this climate?Trevor PelletierRegina, Saskatchewan, Canada
Most of the damage that motor vehicles incur when exposed to extremely low temperatures is the result of compromised lubrication. The most critical element is obviously the engine oil. When your car sits overnight, the oil cools down to the low ambient temperature and thickens. When you fire it up the next morning, the engine is trying to pump a pan that may be full of syrup rather than a nice viscous fluid. Multi-grade oils such as 5W-30 were designed with colder climates in mind-in fact, the W stands for "winter" not "weight" as is widely believed. The purpose of multigrade oil is to provide a single lubricant that will maintain the characteristics of a relatively light oil when cold and display the properties of a heavier oil when hot. This is perhaps an over-simplified explanation, but the general idea is that you can use an oil that will stay thin when chilled to the low ambient temperatures you have to deal with, while still providing ample protection for your engine once it's warmed up.