On another post on 911s about my shifter, yes, it only needed an adjustment, I made reference to the great support here on Pelican and zip on the Aston Martin site (I posted a question on the Aston site two weeks ago and have yet to get a useful response). A few kind souls ( AERKULD and Dentist 930 suggested I post about my oil pump problems, and so here it is.
I'm rebuilding my Aston Martin DB4, its a 1961 and its the first aluminum block engine that Aston made for the street. The big problem with these cars was that the aluminum blocks expanded under heat and the main bearing clearances grew dramatically. As a result, the oil pressure went south rapidly. The company set the main bearing clearances at 3/4 to 1-1/2 thousand of an inch, because when hot the main bearing clearances grew, due to expansion of the aluminum block by three or four times!. My crankshaft has been turned 0.020" on the mains and rods, and the rod clearances are fine so I'm looking at hard chroming the mains back to standard and going for that one thou or so main bearing clearance. The key issue with these engines is oil pressure, oil pressure, especially with a resale potential, not that I'm going to sell the car, but it doesn't matter how much you spent on pistons, valve jobs, etc., its oil pressure.
After all the background, here's the issue. I took my oil pump and inspected it and found that I couldn't pull a 2 thou feeler gauge between the vanes of the pump, which is great. But I have a machined grove of about 55 thou in the oilite bushings on the front and rear of the oil pump shaft that is there (I believe) to make sure that plenty of oil gets through the bushings. I bench tested the oil pump with a blanking plate so that I could use a drill motor (about 500 RPM, I guess) and suck parts cleaning fluid from my parts cleaner into the pump and back out again, and under minimal back pressure (I stuck my finger on the discharge) I got a constant pressure out the back of the oil pump shaft through the machined groove that shot fluid out about five feet. It was discharging the fluid out of the shaft into what would have been the area of the inside of the timig case. To me, when I'm dealing with trying to get LOTS of oil pressure to the mains and I get this huge discharge of oil/fluid out the back of the oil pump shaft under minimal restriction (my finger on the discharge) I see this as a major loss of oil going to the mains. The discharge of oil through the machined oilite bushing grove I don't think is necessary to lubricate the oil pump gear and chain since they're washed in oil anyway.
My thought is to solder the groove shut and at the end of the bushing, and let the oil go towards pressurizing the main bearings. The oilite bushings are no longer available, and I think I get enough oil through the old bushings to lubricate the bushings. This will increase my oil pressure to the main bearings dramatically. Here's a pic of the bushing. I hope I've made sense.
