cadillac flathead 346 valves and guides.

[wicho46]

I removed the intake/exhaust manifold and 2 bottom oil breather's. poured some gas into the intake ports and looks like a couple of the valve guides are worn out. Gas was leaking out the bottom of the valves dripping into the engine .
I have been having an issue of my engine oil being contaminated with gas, swapped out carburetors rebuild fuel pump and NO luck. Looks like I may finally found the issue by maybe having worn out valves and guides. I had the engine rebuild 15years ago and 5000miles put on it since. Do I need to replace the valve's and guides? Is this a hard to do?
Please help. Thanks
L Lopez

[Steve Passmore]

I don't think its surprising that you had gas running through your valve guides if you fill the inlet ports with it, if the valve was closed at that time where else would the fuel go? the guides are not a tight seal and fuel would easily by pass the valve stem in that situation.  In operation the gas is a vapor and the vacuum pull of the engine would take the fuel into the cylinders and little would find its way down the valve stem. 
I'm not saying your guides are not worn but I have worked on engines where the guides are really badly worn and the symptoms of that are burning oil as the vacuum pulls oil the other way, never seen it push fuel down the guides into the engine, if that was happening I don't think those cylinders would be firing.

When you say you have been having fuel in the oil, how can you tell?  If its enough to dilute the oil then its more than would get through the guides.    I have seen this happen with the fuel pump diaphragm split.
On early 346 engines there is a different breather arrangement under the manifold than on later cars.  The breathing was from the valve chest cover into the intake manifold and to prevent fuel finding its way into the engine during a flooding episode there is a loop in the pipe system, later engines are full flow breathing to the outside air down the bell housing.