Why is there no oil to rocker shaft?

Answer 1

I'll attempt to answer this, but I must advise that a Chevy 350 doesn't have shaft mounted rocker arms, so if you are working on a Chrysler or something that does have shaft mounted rocker arms then what I'm advising here won't apply as they are supplied with oil differently. Since this question is posted in the Chevy 350 section, here goes:

A small block Chevy rocker arm receives oil through the pushrod. The oil to the top end goes through two separate oil galleys -- one on each side of the camshaft -- through the lifters and then up through the pushrods. If you look through the distributor hole on a small block with the distributor removed you can see the oil galleys and they run the entire length of the engine block -- this is why you'll never get oil to the rocker arms on an engine that you are priming the oil pump on if a distributor housing is not in the distributor bore to direct the oil flow through the two lifter oil galleys. If you look at a Chevy distributor you'll see a groove about 1/2" or so wide on the bottom of the housing (about an inch or so above the distributor gear) -- that groove directs the oil through the two outer oil galleys that supply the lifters and top end of the engine with oil, and without the distributor housing in the bore the oil being pumped just goes right into the distributor bore and runs right back down on top of the oil pump and back into the pan.

Some stock Chevy distributors do not have the groove that directs the oil through the lifter oil galleries cut all the way around the distributor housing so turning it too far one way or the other if you're messing with the timing or if the distributor is not otherwise in the right position it is possible to block off one lifter oil galley or the other -- depending on which way the distributor is turned and whether or not it is one that doesn't have the groove cut all the way around it.

There's 3 oil galley plugs in the front of the engine block and 3 in the back. If the back ones are missing it will leak like a sieve out the back of the engine all over the ground. If the front ones are missing it will leak internally behind the timing chain. Either way it will be losing oil pressure big time if any of these oil galley plugs are missing. The center oil galley is the main feed for the bottom end of the engine -- pressurized oil runs through the center of the block above the camshaft and diverts through grooves in the block around the outside of each cam bearing down into the main bearings and then out through the crankshaft via the rod and main bearings. The 2 outer oil galleys are the lifter feed oil galleys and this is where the oil to the top of the engine is supplied from. This is basically the entire small block Chevy oiling system aside from the pump and filter passages -- Big blocks are a little different, although the top end is basically oiled the same on a big block, the bottom end is different.

If you are working on a newly rebuilt engine and are not getting oil to the top then start checking things that could be wrong as referenced above.

If, on the other hand, you are working on an engine that has many miles on it and everything else seems in order, it is possible a pushrod is plugged with sludge, or even a lifter can get plugged (believe it or not). Diagnosing this requires you to remove the pushrod for the rocker arm that isn't getting oil and checking it to see if it's plugged. It's also a good idea to check the oil pressure on an engine with a lot of miles on it if you are not getting oil up top. If it's only one rocker arm that isn't getting oil suspect something along the lines of a plugged push rod or lifter.