I am glad you found the leak. The burping sound must totally disappear or you have a leak, however minor. Bolt tightening is a process that ends only after a number of run hours. The gaskets swell intially and they contract a bit. Bolt tightening is a duty of the rebuilder as time progresses immediately after rebuild.
I understand you got a couple of more microns with the tighening, indicating a small leak was sealed.
However, you indicated that you actually achieved rather little in base pressure gain after the rebuild. This is part of my "sleeping dog" theory. (let it lie)
Knowing the normal base pressures of new pumps and typically worn but servicable pumps is a good thing and only comes with time in th' biz. 1400's are low capacity units and even when brand new, never had stellar performance at pumping to much below 10 microns. Used ones are doing good to hit 20 microns. Most used pumps are in terrible shape as regards water, rust and sludge in their guts. The key to turning a used pump around rarely resides in any form of rebuild or take down. The key is to purge all traces of water.
You did this with the fastidious and superb effort with oil changes and long run times. The sludge can retain a tiny amount of moisture, but it will purge in time.
The key is to immediately drain all oil in a newly acquired, used pump. Blank off the inlet. Load it with flushing fluid and run the hell out of it until it is so hot you can barely touch it. Run it ballast open! Drain the fluid. I next put in another batch of flush and run the pump ballast closed, (after an initial ballasting, of course.) Run the thing for a very long time here as well. Now put in a good high viscosity oil and take a pressure check. At 10 microns the 1400 was fine. The sludge made little or no difference once purged of water and other low temp volatiles. If the pump was in the 50 micron region, I would have pulled it apart.
You have certainly spent time and effort on the little 1400 and it should give good service, for as poor as they are at hitting really low base pressures, they are extremely spartan and give long reliable service.
Richard Hull
Created on Wednesday, April 25, 2001 11:22 AM EDT by Richard Hull