Just got my first slant six
You lost me on that last paragraph
The key to Your compression readings is they are within 15%, at that age, that ain't bad. emsvitil pretty much nailed it on the schrader valve, My Craftsman compression
tester ate the original valve, and I didn't know where to get one quickly at the time. So like most gearheads I stuck a wheel valvestem schrader in instead, cars I know
pumped 115-120psi were now reading 90-95psi, the spring in the std valvestem unit is much stiffer than the ones that come in a compression tester.
Another thing to keep in mind is there is a big variance between styles & arrangements of testers. Most good ones have the valve in the end of the hose/adapter, but some
are in the head/gauge assy., this will lower the readings, as will just using the "stepped" threaded end(if it has one) instead of the appropriate long-reach threaded adapter.
Combine a tire valve, the valve at the gauge(basically making the entire hose part of the combustion chamber), and no long-reach adapter, & it'd be no shock to end up
with 35-40psi less than "normal". This of course assumes the gauge is accurate to begin with!!
That's a lot of ash deposit on the plugs, that could be a number of things, but You drove an hour and it didn't smoke. May just need valve stem seals, a valve adj. and a
tune-up. The oil pressure, try an oil change and 10w-40, see what You've got. They've got all of the usual suspects covered for You^^above. BE AWARE, the Slanty fuel
pump is upside down so to speak, if the diaphragm starts leaking, it won't just start leaking/squirting out of the breather on the pump body. It will trickle/run/dribble
right into the crankcase long before it gets bad enough to start hosing out of the breather(or vent) hole. If it's old, it's just a matter of time...................................
