Q: I have a Ford 390 engine. I had the block re-bored and was told to use moly piston rings. When I was finished with the rebuild, the engine began to use oil, so I tore it apart to see what was wrong with it. The cylinder walls were very wet (oily), as were the intake valves.
According to my Ford manual, the ring gaps should have been .015-inch to .023-inch for the top rings and .010-inch to .020-inch for the secondary rings. The top rings were within the specified tolerances, but the secondary rings were not. The oil control rings didn’t seem to have much tension in them, either.
What do I need to do to correct this problem? Is there a better valve seal than the stock seals I am using?
A: Now that you have the engine torn apart, you are going to have to re-hone your cylinders and get a fresh set of piston rings. The ideal scenario would have been to conduct a leakdown test to determine how the rings were sealing before you tore the engine apart. Even a compression test would have been a better idea, as the problem may not have been with the rings at all.
As for the valve seals, PTFE seals are best. However, you will have to machine the valve guides to use them.