Blow by and Carburetor Questions

[hbabler]

Could I run the line with the PCV on it to catch can to see if anything comes out? Or does it have to have vacuum to work. Also should the rear vent line push oil out? I had run it into a can for a couple of days and I did not find any oil in that can.

[Stuka]

Vacuum typically has an impact on if oil is going to come out or not. My guess is you would not see anything if it was just sitting in a catch can.

[hbabler]

Ok the rear vent line is clear. Any other ideas? What can I do to rule out excessive crank case pressure? Or what can I do to mitigate it?

[68glad]

Following this closely. My 401 doing the same thing. Blows the fill cap off @ high rpm's. New pcv installed correct way.

[Stuka]

I think, for both of you, do a compression test with it cold, warm, and if you can, with a squirt of oil in each cylinder.

Although in the case of the OP, I think with as much oil as you have in the intake, your compression numbers are wet. Which means, your "dry" numbers may be much lower.

Unfortunately I am thinking you both have blow by. Either due to bad rings, or warn cylinder walls. With AMC's it is typically rings.


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[hbabler]

I have pretty much resigned myself to the fact that I am going to have to put new rings in this thing, I have figured out a short term solution in that I have added an oil separator inline between the pcv valve and the carb and it seems to be working pretty well.

[carnuck]

For the carb, its possible you have a vacuum leak. The Weber uses a 2 piece adapter setup. Twice I have had to pull mine apart and re-tighten the bottom adapter. It uses these allens that can come loose.

Push oil out the valve cover typically means the cylinders are pressurizing the crank case and the PCV is plugged, making it go out the other hole. But you have good compression (120 is within factory specs). Strange.

I put double star anti-rattle washers to keep those from coming loose.

The ones I have come loose are recessed allens. You cannot put washers on them unfortunately.

Better check that again. I even found cone shaped ones for tapered head screws.

[carnuck]

I have pretty much resigned myself to the fact that I am going to have to put new rings in this thing, I have figured out a short term solution in that I have added an oil separator inline between the pcv valve and the carb and it seems to be working pretty well.

I've done that on lots of high mileage rigs.

[letank]

Same here, blow by on the 74, if i leave the oil filler cap off.... I can see the oil smoke on throttle down.. 349k on oem engine, working on a catch can, compression 140-145, idle at 21" at sea level, air filter fills up slowly.
Pict of your catch can set up, plz.
Trying ti figure out the best location....

[Stuka]

Same here, blow by on the 74, if i leave the oil filler cap off.... I can see the oil smoke on throttle down.. 349k on oem engine, working on a catch can, compression 140-145, idle at 21" at sea level, air filter fills up slowly.
Pict of your catch can set up, plz.
Trying ti figure out the best location....

140-145? Are you sure it has that many miles on it? Factory specs out 120-150, with 150 being brand new. If you are getting oil coming out, you are probably closer to the 110-120psi area on at least one cylinder.

[letank]

Same here, blow by on the 74, if i leave the oil filler cap off.... I can see the oil smoke on throttle down.. 349k on oem engine, working on a catch can, compression 140-145, idle at 21" at sea level, air filter fills up slowly.
Pict of your catch can set up, plz.
Trying ti figure out the best location....

140-145? Are you sure it has that many miles on it? Factory specs out 120-150, with 150 being brand new. If you are getting oil coming out, you are probably closer to the 110-120psi area on at least one cylinder.

Owned since 1983 at 78Kmiles, the last compression was done less than 2Kmiles ago.

[Stuka]

Same here, blow by on the 74, if i leave the oil filler cap off.... I can see the oil smoke on throttle down.. 349k on oem engine, working on a catch can, compression 140-145, idle at 21" at sea level, air filter fills up slowly.
Pict of your catch can set up, plz.
Trying ti figure out the best location....

140-145? Are you sure it has that many miles on it? Factory specs out 120-150, with 150 being brand new. If you are getting oil coming out, you are probably closer to the 110-120psi area on at least one cylinder.

Owned since 1983 at 78Kmiles, the last compression was done less than 2Kmiles ago.

Interesting. Makes me wonder how you could be getting blow by then. As those numbers are very high, and way higher than mine at 241k (mine are all sub 120psi).

[Florida83FSJCherokee]

Ok. My 258 is producing high pressure as well. My compression numbers were also high. Im also getting the oil through the pcv line into the intake. My thread has a pic of the filter I added to catch the oil (last post ish...)

In regusrds to which line will collect the oil it just depends which line is pulling vacuum ans which.is provideing air intake. The pcv on my rig runs into the booster port below the card so the breather in the pack provides the clean air draw. If you switch them it would just reverse the flow.

So yes, tbe rings are going to need replacement but I'm confused as to how the pressure is able to get that high if your not burning any oil. So in both our cases the pressure shouldn't get high enough to force oil out especially with new pcv valve and breather.

In a previous post someone mentioned clogged exhaust. My system is totally shot and I have been getting a steady increase in my exhaust gasket failing the more I replace things That improve performance. Its next on the list of replacement but I've been waiting because I didn't want to invest the effort if the engine was going to be rebuilt.

So. Am I wrong to think that the non functional exhaust possibility could create enoughpressure to force oil into the pcv exit line and down into the intake?

I'm on my phone and cannot attach pics but if you look at the filter I installed on my thread you can see the huge amount of oil I got in 6! Miles. The oil cap was also leaking on top of the cover even with everything replaced. I'm not saying the valves and rings couldn't use a refurb but that much oil in 6 miles with no smoke and an engine that is running better than ever says there is more to the pressure issue than the rings....

THANKS,
JP

[carnuck]

Even the 4.0L in my Comanche has blowby when loaded up. I'm switching to Napa 15W50 synthetic from Delo 15W40 which usually knocks the blowby to 1/2. In 4,000 miles I have used less than 1/2 qt of oil. It's normal when the miles get up there. The incoming pressure gets down past the rings on the compression and ignition stroke, but that doesn't mean the oil goes back up the other way because the rings flex up and down the cylinder walls as the pistons reverse direction.
A blowby catcher with a PCV on it and a breather tube that drops down to the back bumper is how we did it in the old days. Water can't be drawn up that way unless you do a deep water crossing

[tgreese]

You can still fit a blow-by catcher. Use a can or similar filled with some kind of filter material like copper or stainless wool (copper dish scrubbies?) to catch the oil. Put the inlet at the bottom so the catched oil will drain back to the valve cover. It's a kludge, but it will keep oil out of your air cleaner.

[carnuck]

I did mine on my '83 Cherokee so the oil drained back to the oil pan but it was easy because I had the pan off already for the rear main seal repair.