It's been five years since my engine rebuild and everything was working just fine until two weeks ago. I started Lurch up for a drive and there was no oil pressure. ;-(
I went around the block once to see if it would come up but it did not.
I first checked the oil gauge by disconnecting the tube going to it and blowing a little compressed air into the back of the gauge. The gauge popped up so the gauge is good. So I reattached the input tube.
My next step in the investigation was to pull the distributor and run the oil pump with a screwdriver shaft in a portable drill to see if the pump is working. Before I pull the distributor, however, I set cylinder one on top dead center (TDC) to facilitate putting the distributor back in later. On Lurch's flywheel, the U|C (TDC) mark is hard to see so five years ago, I touched a spinning drill bit to the line between the U and the C and put a drop of bright orange paint on it to make it stand out. See the first couple of pics below.
I also marked which wire went to which cylinder because chances are that I'd have to pull them off the distributor cap. After loosening the distributor advance/retard plate, I lifted the distributor out of its hole in the block. Then, I took the distributor cap off and lifted the wire conduit up to give me some room to work over the distributor hole. See the fourth pic below.
With the distributor out, you can look down the hole and see the top of the oil pump shaft with a slot in it that should receive the lower pin of the distributor driving gear.
The next 'issue' I faced was that my portable drill with a screwdriver shaft did not fit in the space between the top of the distributor hole and the exhaust manifold. Invent a tool to the rescue! I took the screwdriver shaft and welded it to a hex head that fit into a 90 degree drill adapter so I could have the portable drill sticking out sideways to spin the oil pump. See photos six and seven.
When I spun the oil pump with the drill, the oil pressure gauge now ticked up, so the oil pump is good. ;-)
I suspect the overall problem here was that the distributor was not seated all the way down and therefore was not driving the oil pump. Hmmm. I might not have installed the distributor correctly back in 2017 and it was just sitting on top of the oil pump shaft and driving it by friction, rather than by the positive force of the bottom pin of the distributor gear sitting inside the oil pump shaft slot.
To support this theory, the distributor gear has wear marks that are towards the bottom of the gear instead of the middle of the gear. Also, the bottom pin of the distributor gear shows some wear like it was riding on top of the oil pump shaft. See pics eight and nine.
Since the distributor would not have worked its way up and out of the oil pump shaft over time (because the advance/retard plate kept it in place, I came to the conclusion I last installed the distributor incorrectly (it wasn't seated all the way down). Darn! I've only driven Lurch a couple of hundred miles since the engine rebuild and I'm thankful that the oil pump has been spinning all this time (until now...).
So the big question is, "How do I KNOW DEFINITELY when the distributor is fully seated and fully engaging the oil pump?"
I posed that question to some VCCA members and two (Ron Beam and Chip Sweet) gave me the answer. Although they have done so many engines that they have a 'feel' for it, they suggested measuring the depth of the distributor hole (from the top of the clamp plate to the top of the bearing washer on the oil pump) and then put a mark on side of the distributor body that I can SEE, which will tell me if the distributor body is down all the way or still sticking up above the oil pump shaft. BRILLIANT!!
Photo 16 shows a long screwdriver in the distributor hole and me marking where it meets the clamp plate with a Sharpie pen. Photo 17 shows that the depth of the hole is 2.750 inches. Yes!! This measurement should work for all '26, '27, and '28 engines. Photo 18 shows the bottom roll pin being inserted into the distributor gear.
Photo 19 shows the hole-depth-indicating mark I made on the side of the distributor. Building upon the flat washer experiment above, I put a small strip of paint masking tape on the top of the distributor shaft to show me the orientation of the bottom pin in the distributor gear. This is shown in photo 20.
As an aside, as Ray Holland (AntiqueMechanic) mentioned in his "School is in Session" document, the July 1927 Chevrolet Service News (page 27) discusses the process of installing the distributor. This description, however, does not discuss how to get the distributor shaft to properly line up with the oil pump shaft.
Photo 21 shows the distributor in its hole, but NOT aligned properly with the oil pump shaft slot. As you can see in the photo, the hole-depth-indicating mark is about 3/8 of an inch above the clamping plate. That is proof positive that the distributor is NOT FULLY SEATED AND IS NOT IN THE OIL PUMP SHAFT SLOT.
Drum roll please!!
After correctly orientating the oil pump shaft slot, I dropped the distributor into its hole and (YAY!!) the hole-depth-indicating mark has dropped further down and is now close to the clamping plate. See photo 22.
Now I am confident that I can positively determine if the distributor is fully seated and fully engaged with the oil pump shaft slot. I pulled the distributor out again, put some assembly grease on the gear (photo 23), and dropped it in the hole for the last time (photo 24). I was careful not to get any assembly lube on the inside of the clamp plate hole.
You might have noticed that at the top of this thread, I positioned the crankshaft at TDC (U|C) instead of 25 degrees before TDC and set the retard/advance lever at fully retarded (as opposed to fully advanced), as recommended by the literature.
To my thinking, I want to ensure that when I'm starting the engine, I want to KNOW that the spark is happening AT TDC (not before TDC at all), rather than relying on the levers to get it close when the engine is timed for the spark to be fully advanced (25 degrees before TDC). I've found this makes for an easy starting engine and it seems to perform just fine when I fully advance the lever for driving.
A couple of days after I put the distributor back in, I took Lurch out for a 10 mile drive. Everything went extremely well! In fact, the oil pressure is higher than it was before this episode. I now get 18 psi at cold start and it drops to 5 psi at idle when warm. This is with a gear-type oil pump that I put in during the 2017 engine rebuild. Here's a link to that adventure: Resurrecting a '28 4 Banger
