Could a partially "unseated" oil pressure bypass valve; maybe a contaminant of some sort on the valve seat, manifest itself as low oil pressure.

Yes

In a continental O-300, definitely yes. Easy fix, take it apart and polish the piston and housing in a lathe and put it back together. Don't be surprised if you find 1 or 2 washers behind the spring when you take it apart, put them back in when you finish. If you want to replace the spring while you're at it, they only cost about $25.00.

Dale Moul wrote:In a continental O-300, definitely yes. Easy fix, take it apart and polish the piston and housing in a lathe and put it back together. Don't be surprised if you find 1 or 2 washers behind the spring when you take it apart, put them back in when you finish. If you want to replace the spring while you're at it, they only cost about $25.00.

Can a similar thing be said for a Lyc 0-360 ?

Yes in my case it was a was metal from engine failing no part number on it but big enough to warrant tear down.
DENNY

I pulled the filter, no metal found so it seem the pump isn't self destructing. I'll be checking the condition of the oil pressure relief vale seat next for damage, contaminant etc. and the integrity of the spring as well. Previously I had stable oil pressure in the mid 60's, on the last flight it dropped into the high 20's range.

60 is kind of low for a Lycoming.
DENNY

DENNY wrote:60 is kind of low for a Lycoming.
DENNY

Others has suggested that as well, what is a more normal value in your opinion ? From what I've been reading the nominal range seems to be between 60-90 psi.

This site is great for gaining a broad spectrum of intel, its all appreciated.

Thanks

Somewhere along the road I saw a SB that recommended raising the oil pressure. Oil temp/RPM will effect pressure but at 2400 RPM and 180 degree oil temp I will usually see about 80 psi. High 90s at 40 degree start up. It drops to zero real fast when you blow out the gasket on the governor blank out plate. Continental engines take oil pressure reading from the end of the line so they have lower pressure recommendations.
DENNY

We've had strangely similar experiences........

It drops to zero real fast when you blow out the gasket on the governor blank out plate.

I'm looking at the Lycoming 0-360A IPC and it appears the older style oil pressure relief valve that uses washer/spacers to increase/decrease oil pressure can be replace with the external adjustable type. Has anyone done this or know if this is in fact possible, seems like a good idea to my way of thinking.