I finished installing the GMC 270 I've spent the last few months rebuilding. This is my first engine rebuild and I did every thing under the close watch of a mechanic friend of mine who has built and raced cars his whole life.
It has new rod and main bearings, rebuilt head, chrome piston rings, and new oil pump. the lower end had been rebuilt at some point and the cam and crank looked like new. In hind site I should have left it alone.
On Monday I primed the oil pump with a half inch drill and the shaft of an old dizzy. My wife was in the truck watching the oil gauge and said every time I ran the drill the pressure went up to 30 psi. My friend said that was good but now I wonder if it should have been closer to 60 psi. I had good oil flow to all the rockers.
Yesterday I checked engine and dizzy timing, valve lash, carb settings, etc. and fired the engine up. It was hard to keep running at first but with a little tweeking of the timing, choke, and idle, she ran and sounded good. I did notice what I thought might be a slight miss as I ran around the truck to get in and back out of the shop. I wanted it outside because the exhaust was a bit stiff in the small shop due to the chrome piston rings. As I was backing out I could feel that the engine ran kind of rough, like the "miss' was more pronounced. I glanced down at the oil gauge and it read -0-! I killed the engine.
When My friend showed up he accused me of not getting the dizzy seated all the way but after checking, he found it was all the way in. We intalled an aftermarket oil gauge and he had me fire the truck back up. It runs great but has a low end knock and oil pressure was maybe 10 to 12 psi. After he left I pulled the dizzy and used the drill to turn the pump and found that the rear main seal is leaking bad, but it didn't lose a drop when the engine was running.
All the external oil lines are rerun using the original fittings and new lines the same diameter as the old lines.
(1) I need to know what the heck just happened. It took me months to build this because I was meticulous. Everything was to specs, and my friend double checked every thing I did.
(2) I also just needed to vent. This is my daily driver and now I'm walking. Rebuiling is out of the question because the costruction outfit I was working for didn't survive the winter, so funds are tight to non existant.
I pulled the oil filter and it's clean and I drained the $75.00 worth of high zinc oil and found no metal shavings but it had a slight metallic sheen. Felt smooth, no grit.
So, what happened? What did I do wrong?
