oil and instant fouling

[wl_walker]

I have a 1960 C10 short step side with a 350 ci motor. Block code indicates it's a 1969 and is a 4-bolt main. Previous owner had the motor 'refreshed' which means just that the seals were redone most likely. No1 and 7 cylinders have oil intrusion and is fouling the spark plugs almost immediately. All cylinders are showing 155 to 160 compression. I also have a rattle sound from under the hood that seems to be valve train, only hear it when at speed over 45 mph. New plugs, plug wires, rotor and cap. My thought is this: I'm hearing the valves rattle in the guides, oil is entering at the valve guides, time to pull the heads and have at minimum the guides and seals done. I don't expect a diagnosis, just a friendly discussion about past experience and possibilities...

EDIT: I also have a bit of smoke coming form the crankcase. When I remove the PCV I see it. Might be combustion in the 'bad' cylinders pushing past the intake guide after the exhaust valve closes?

[jayoldschool]

Have the valve seals been replaced? Cheap and easy to do. Solved the oil smoke puff on startup on my 327. It also fouled #8 to failure. I put the modern seals on it on both I and E and it is great.

[RustyPile]

Valves don't "rattle in the guides", at least not so as can be heard. The sound you're hearing may or may not be related to oil fouling plugs. Oil intrusion into the combustion chamber can dilute the fuel/air mixture and lower the octane.. This can cause detonation that makes a sound like shaking a can of marbles. Another source of detonation is excessive base timing setting.

How much oil does the engine actually consume at, say, 1,000 miles?? Any more than a quart in 800 miles will be considered excessive by most opinions. Worn rings can also be the source of your oil fouling and consumption.. As others have stated, the cheapest and easiest approach would be to replace valve stem seals.. If that doesn't help the situation, it's time for a rebuild.

[wl_walker]

Oil consumption is high at least 1/2 quart in 300 miles. The rattle is heard while cruising with light throttle, I would expect, if it were pinging I hear, to get worse under greater load which I don't. It goes away. Since compression is 155-160 per cylinder including the suspect one it would seem to me that the valve seals and rings are doing their job. I agree that the initial thing would to do valve stem seals. Just that I always open the 'can of worms' lol

[RustyPile]

Originally Posted by wl_walker

Oil consumption is high at least 1/2 quart in 300 miles. The rattle is heard while cruising with light throttle, I would expect, if it were pinging I hear, to get worse under greater load which I don't. It goes away. Since compression is 155-160 per cylinder including the suspect one it would seem to me that the valve seals and rings are doing their job. I agree that the initial thing would to do valve stem seals. Just that I always open the 'can of worms' lol

If the advance mechanism vacuum source is drawn from the intake manifold as opposed to ported vacuum, at light loaded cruise the vacuum will be high and, depending on the vacuum advance "curve", could be at maximum advance.. Under greater load or accelerating, the vacuum will go lower, pulling out some of the timing --- pinging disappears..

Don't be fooled by your compression readings.. Quite often worn rings will indeed exhibit good compression. Have you conducted wet/dry compression tests??. At the rate of your oil consumption, valve seals will help some, but will not totally cure that.. I'm afraid you have a well worn engine. Do the seals and see what happens.. Another thing to consider is oil leaks.. If your engine "marks its territory" there's part of your problem.

{EDIT} The can of worms theory always applies when working on these old trucks. There's no getting around it..

[vince1]

The last engine (250) I took apart had stuck oil rings. Freeing them up may have got me some more miles but it was due to come apart for repair anyways. Seals were gone and the camshaft lobes were ready to be worn off. I think it was original.

[wl_walker]

Thanks for the replies, going to try stem seals and go from there. As well as a leak down test. The cam is new btw, mild “RV cam”.

[Grounded63]

Valve seals only control oil for the stems/guides.

Compression is sealed by the valve face/seats.

If the cam is new, and wasn't installed by you. You may need to check the preload on the lifters. And possibly check that it hasn't lost a lobe.

Refreshed, should generally mean it was re-ringed, re-bearinged, and seals/gaskets. But, not machined. Otherwise it would just be described as resealed.

[jayoldschool]

When I did my seals, I used this thread for advice, and bought the seals in post#4

https://nastyz28.com/threads/valve-stem-seals.207554/

[wl_walker]

I've used positive seals before, two things I had to do first: install self-lubricating guides an to machine the boss so that they can fit. I haven't taken the springs off yet, need to see what's going on in there. I have both positive seal and umbrellas with O-rings on hand so I'm ready either way. If this doesn't work, and depending on what I get out of the leak-down test, will determine next steps which will be to pull the heads and have my local machine shop look them over as well as see what if anything is going on with the head gaskets.

[theastronaut]

Originally Posted by wl_walker

I also have a bit of smoke coming form the crankcase. When I remove the PCV I see it. Might be combustion in the 'bad' cylinders pushing past the intake guide after the exhaust valve closes?

On my old autocross car with poor ring seal, I had to add a catch can/air oil separator to keep oil mist/blowby from getting into the intake through the pcv system. Its worth making a temporary can from and old bottle and some pot scrubbers to separate oil from air before it goes into the intake to see if that helps any.