Yep, it's unfortunately true. As smoothly as my slant 6 purrs like a kitten, it's nevertheless old and tired, and I need to start collecting rebuild parts.

The main question is this: it appears to be spitting oil out the breather cap, and I'm trying to understand exactly why. The PCV valve is sucking pretty hard, when I test it at idle by plugging it with my finger. But apparently, it is not sucking sufficiently to overcome whatever pressure is building up in the crankcase? The breather cap (the oil filler location) is dripping oil all over the valve cover, and hence all over the engine and on the road. We're talking about several drops of oil hitting the pavement, after I shut it down from a 10 mile trip. I have no idea how much oil leaves the engine during such a trip. I thought about fabricating a donut-shaped catch can, just out of curiosity, but haven't done it.

I thought the engine was pretty healthy, until I did a compression test. Those readings are 80-85 psi, cranking and hot, WOT. If I squirt a little motor oil into the hole, spin it a few revolutions, and put the gauge on it again, each reading is higher by only 3-4 psi. I figured that meant the rings are not being helped very much by the oil, so the problem must therefore be valve sealing.

To verify, I built a hose to connect my air compressor to a spark plug hole. It's sort of a leakdown tester except I have no gauge on it... all I want to do is find out where the air pressure disappears, by listening. As expected, I can hear it whistling out the carb and/or the exhaust pipe, depending on which cylinder. But to my surprise, for a couple of cylinders, air whistles pretty darn well out the dipstick tube. So it appears that this engine suffers from a multitude of ills, depending on which cylinder we're looking at, which makes it all the more remarkable that the compression is so incredibly even.

I'm not sure why my compression (wet/dry) test seems to indicate very little problems with the rings, but the leakdown test shows issues. I tend to believe the leakdown.

Rings in cylinders 1 and 3 are the worst offenders, and I'm sure that they are contributing to combustion pressure ending up in the crankcase. My theory is that air (well, dirty air) is entering the crankcase faster than the PCV can suck it out, and since the remaining pressure has to go somewhere, the breather cap is the route. And it picks up oil droplets on the way out, through the filter mesh. Does this make sense? Or is there something I'm missing, here?

Now for the weird part. (For anyone who hasn't fallen asleep yet. ) All of the above suggests problems that have slowly gotten worse over time. But to the best of my knowledge, this oil spitting problem happened suddenly. I don't recall it dripping on the pavement, last time I had it licensed in 1999. The compression was weak, yes, but everything else was good. The car then sat for 3 years, and I recently tuned it up, adjusted valves that had worked themselves quite tight before I quit driving it, and put it on the road. Oil consumption, based on the few hundred miles I've driven this season, seems to be at the same 1000 miles/quart figure that I remember it used to be. Oil pressure still won't go below 50 psi no matter what, which tells me the bearings are in good shape. And yet now, all of a sudden, it spits out the breather cap.

Am I going insane? (No wait, don't answer that.) It just seems like I'm missing a piece of the puzzle. I'm planning to rebuild the thing, anyway, but I'd really like to fully understand what it's doing now.

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Classic symptoms of worn rings.

Yea, thanks... I guess I kinda figured that. But could it really happen all of a sudden? That's the part I don't understand...

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

I second what Eric said. Worn rings. I had the same thing happen on my 84 Ford van. It could be sudden. The clearance has to reach the point where it is out of spec someday.

Reed

Oh yes, it can happen all of the sudden. On my original engine, I jumped into traffic one day and had to push it hard to get up to speed. At the next traffic light, the engine had a severe miss at idle. Got home and did a compression test on it. The #4 cylinder had 20lbs of compression, with oil added it only had around 23 or so lbs. Broken ring is my guess. I did my wife and I did drive it like that for a year or so (she short trips around town, me 80 mile round trip to work). Just had to replace the air filter every week. I never found out what it was, I just pulled it and put a '73 225 from a Dart in.

Erik, It's possible, the rings stuck in the piston grooves, while the engine was sitting. Not uncommon.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Aaaaaaahh! OK, that makes sense.

So that means the rings cannot expand when warm, and therefore cannot close the gap to the appropriate tolerance...? Therefore the combustion gasses blow right past the gaps. Gotcha.

As far as running it the way it is, right now... does that mean that the rings are under tension as they try to expand but cannot, and are therefore at risk of breaking, while inside the piston lands? I can imagine that as soon as one breaks, the risk of scuffing the cylinder walls is tremendously increased. Or does a broken ring just rattle around in the piston land and wear down the shoulders of the lands, while causing minimal damage to the cylinders? I've heard of people running old tired engines for years... although I hope to rebuild this one before next summer.

Ya know, it's funny that, in all the discussion I've seen over the years about how to properly store an engine and then prep it for running, lots of people talk about corrosion, and oil on surfaces... but no one has ever mentioned stuck piston rings. Interesting. Learn something new every day.

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Ah ha! Thanks for the tip... I think that gives me insight to my other question, as to why the wet/dry testing method might not show a problem with rings. Normally, if it's just a case of worn rings, adding extra oil can seal it enough to bring the reading up. But if the ring is broken, there's no outward sealing pressure on the cylinder walls, so there's a gap far too wide for oil to be able to seal. Likewise, if the ring is stuck, the end gap could be too wide for the oil to make any improvement.

Goodness, if I keep this up, I might actually become smart.

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

The reason, I thought of it was. Those slant engines, I have on the stand, a couple had stuck rings. One ring is so bad I'm haveing trouble getting it removed from the groove. However none were broken. One piston also had a frozen piston pin. Got the wife mad, by putting the piston/rod assy in the oven at 400*. That allowed me to loosen up the pin. All these engines were running when pulled, within the last couple of years, and were stored inside since then.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225